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pcre2api(3)
PCRE2API(3) Library Functions Manual PCRE2API(3)
NAME
PCRE2 - Perl-compatible regular expressions (revised API)
#include <pcre2.h>
PCRE2 is a new API for PCRE, starting at release 10.0. This document
contains a description of all its native functions. See the pcre2 docu‐
ment for an overview of all the PCRE2 documentation.
PCRE2 NATIVE API BASIC FUNCTIONS
pcre2_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length,
uint32_t options, int *errorcode, PCRE2_SIZE *erroroffset,
pcre2_compile_context *ccontext);
void pcre2_code_free(pcre2_code *code);
pcre2_match_data *pcre2_match_data_create(uint32_t ovecsize,
pcre2_general_context *gcontext);
pcre2_match_data *pcre2_match_data_create_from_pattern(
const pcre2_code *code, pcre2_general_context *gcontext);
int pcre2_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);
int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext,
int *workspace, PCRE2_SIZE wscount);
void pcre2_match_data_free(pcre2_match_data *match_data);
PCRE2 NATIVE API AUXILIARY MATCH FUNCTIONS
PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data);
uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);
PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);
PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);
PCRE2 NATIVE API GENERAL CONTEXT FUNCTIONS
pcre2_general_context *pcre2_general_context_create(
void *(*private_malloc)(PCRE2_SIZE, void *),
void (*private_free)(void *, void *), void *memory_data);
pcre2_general_context *pcre2_general_context_copy(
pcre2_general_context *gcontext);
void pcre2_general_context_free(pcre2_general_context *gcontext);
PCRE2 NATIVE API COMPILE CONTEXT FUNCTIONS
pcre2_compile_context *pcre2_compile_context_create(
pcre2_general_context *gcontext);
pcre2_compile_context *pcre2_compile_context_copy(
pcre2_compile_context *ccontext);
void pcre2_compile_context_free(pcre2_compile_context *ccontext);
int pcre2_set_bsr(pcre2_compile_context *ccontext,
uint32_t value);
int pcre2_set_character_tables(pcre2_compile_context *ccontext,
const unsigned char *tables);
int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext,
uint32_t extra_options);
int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext,
PCRE2_SIZE value);
int pcre2_set_newline(pcre2_compile_context *ccontext,
uint32_t value);
int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext,
uint32_t value);
int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext,
int (*guard_function)(uint32_t, void *), void *user_data);
PCRE2 NATIVE API MATCH CONTEXT FUNCTIONS
pcre2_match_context *pcre2_match_context_create(
pcre2_general_context *gcontext);
pcre2_match_context *pcre2_match_context_copy(
pcre2_match_context *mcontext);
void pcre2_match_context_free(pcre2_match_context *mcontext);
int pcre2_set_callout(pcre2_match_context *mcontext,
int (*callout_function)(pcre2_callout_block *, void *),
void *callout_data);
int pcre2_set_offset_limit(pcre2_match_context *mcontext,
PCRE2_SIZE value);
int pcre2_set_heap_limit(pcre2_match_context *mcontext,
uint32_t value);
int pcre2_set_match_limit(pcre2_match_context *mcontext,
uint32_t value);
int pcre2_set_depth_limit(pcre2_match_context *mcontext,
uint32_t value);
PCRE2 NATIVE API STRING EXTRACTION FUNCTIONS
int pcre2_substring_copy_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen);
int pcre2_substring_copy_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR *buffer,
PCRE2_SIZE *bufflen);
void pcre2_substring_free(PCRE2_UCHAR *buffer);
int pcre2_substring_get_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR **bufferptr, PCRE2_SIZE *bufflen);
int pcre2_substring_get_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR **bufferptr,
PCRE2_SIZE *bufflen);
int pcre2_substring_length_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_SIZE *length);
int pcre2_substring_length_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_SIZE *length);
int pcre2_substring_nametable_scan(const pcre2_code *code,
PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last);
int pcre2_substring_number_from_name(const pcre2_code *code,
PCRE2_SPTR name);
void pcre2_substring_list_free(PCRE2_SPTR *list);
int pcre2_substring_list_get(pcre2_match_data *match_data,
PCRE2_UCHAR ***listptr, PCRE2_SIZE **lengthsptr);
PCRE2 NATIVE API STRING SUBSTITUTION FUNCTION
int pcre2_substitute(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext, PCRE2_SPTR replacementzfP,
PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer,
PCRE2_SIZE *outlengthptr);
PCRE2 NATIVE API JIT FUNCTIONS
int pcre2_jit_compile(pcre2_code *code, uint32_t options);
int pcre2_jit_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);
void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);
pcre2_jit_stack *pcre2_jit_stack_create(PCRE2_SIZE startsize,
PCRE2_SIZE maxsize, pcre2_general_context *gcontext);
void pcre2_jit_stack_assign(pcre2_match_context *mcontext,
pcre2_jit_callback callback_function, void *callback_data);
void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);
PCRE2 NATIVE API SERIALIZATION FUNCTIONS
int32_t pcre2_serialize_decode(pcre2_code **codes,
int32_t number_of_codes, const uint8_t *bytes,
pcre2_general_context *gcontext);
int32_t pcre2_serialize_encode(const pcre2_code **codes,
int32_t number_of_codes, uint8_t **serialized_bytes,
PCRE2_SIZE *serialized_size, pcre2_general_context *gcontext);
void pcre2_serialize_free(uint8_t *bytes);
int32_t pcre2_serialize_get_number_of_codes(const uint8_t *bytes);
PCRE2 NATIVE API AUXILIARY FUNCTIONS
pcre2_code *pcre2_code_copy(const pcre2_code *code);
pcre2_code *pcre2_code_copy_with_tables(const pcre2_code *code);
int pcre2_get_error_message(int errorcode, PCRE2_UCHAR *buffer,
PCRE2_SIZE bufflen);
const unsigned char *pcre2_maketables(pcre2_general_context *gcontext);
int pcre2_pattern_info(const pcre2 *code, uint32_t what, void *where);
int pcre2_callout_enumerate(const pcre2_code *code,
int (*callback)(pcre2_callout_enumerate_block *, void *),
void *user_data);
int pcre2_config(uint32_t what, void *where);
PCRE2 NATIVE API OBSOLETE FUNCTIONS
int pcre2_set_recursion_limit(pcre2_match_context *mcontext,
uint32_t value);
int pcre2_set_recursion_memory_management(
pcre2_match_context *mcontext,
void *(*private_malloc)(PCRE2_SIZE, void *),
void (*private_free)(void *, void *), void *memory_data);
These functions became obsolete at release 10.30 and are retained only
for backward compatibility. They should not be used in new code. The
first is replaced by pcre2_set_depth_limit(); the second is no longer
needed and has no effect (it always returns zero).
PCRE2 EXPERIMENTAL PATTERN CONVERSION FUNCTIONS
pcre2_convert_context *pcre2_convert_context_create(
pcre2_general_context *gcontext);
pcre2_convert_context *pcre2_convert_context_copy(
pcre2_convert_context *cvcontext);
void pcre2_convert_context_free(pcre2_convert_context *cvcontext);
int pcre2_set_glob_escape(pcre2_convert_context *cvcontext,
uint32_t escape_char);
int pcre2_set_glob_separator(pcre2_convert_context *cvcontext,
uint32_t separator_char);
int pcre2_pattern_convert(PCRE2_SPTR pattern, PCRE2_SIZE length,
uint32_t options, PCRE2_UCHAR **buffer,
PCRE2_SIZE *blength, pcre2_convert_context *cvcontext);
void pcre2_converted_pattern_free(PCRE2_UCHAR *converted_pattern);
These functions provide a way of converting non-PCRE2 patterns into
patterns that can be processed by pcre2_compile(). This facility is
experimental and may be changed in future releases. At present, "globs"
and POSIX basic and extended patterns can be converted. Details are
given in the pcre2convert documentation.
PCRE2 8-BIT, 16-BIT, AND 32-BIT LIBRARIES
There are three PCRE2 libraries, supporting 8-bit, 16-bit, and 32-bit
code units, respectively. However, there is just one header file,
pcre2.h. This contains the function prototypes and other definitions
for all three libraries. One, two, or all three can be installed simul‐
taneously. On Unix-like systems the libraries are called libpcre2-8,
libpcre2-16, and libpcre2-32, and they can also co-exist with the orig‐
inal PCRE libraries.
Character strings are passed to and from a PCRE2 library as a sequence
of unsigned integers in code units of the appropriate width. Every
PCRE2 function comes in three different forms, one for each library,
for example:
pcre2_compile_8()
pcre2_compile_16()
pcre2_compile_32()
There are also three different sets of data types:
PCRE2_UCHAR8, PCRE2_UCHAR16, PCRE2_UCHAR32
PCRE2_SPTR8, PCRE2_SPTR16, PCRE2_SPTR32
The UCHAR types define unsigned code units of the appropriate widths.
For example, PCRE2_UCHAR16 is usually defined as `uint16_t'. The SPTR
types are constant pointers to the equivalent UCHAR types, that is,
they are pointers to vectors of unsigned code units.
Many applications use only one code unit width. For their convenience,
macros are defined whose names are the generic forms such as pcre2_com‐
pile() and PCRE2_SPTR. These macros use the value of the macro
PCRE2_CODE_UNIT_WIDTH to generate the appropriate width-specific func‐
tion and macro names. PCRE2_CODE_UNIT_WIDTH is not defined by default.
An application must define it to be 8, 16, or 32 before including
pcre2.h in order to make use of the generic names.
Applications that use more than one code unit width can be linked with
more than one PCRE2 library, but must define PCRE2_CODE_UNIT_WIDTH to
be 0 before including pcre2.h, and then use the real function names.
Any code that is to be included in an environment where the value of
PCRE2_CODE_UNIT_WIDTH is unknown should also use the real function
names. (Unfortunately, it is not possible in C code to save and restore
the value of a macro.)
If PCRE2_CODE_UNIT_WIDTH is not defined before including pcre2.h, a
compiler error occurs.
When using multiple libraries in an application, you must take care
when processing any particular pattern to use only functions from a
single library. For example, if you want to run a match using a pat‐
tern that was compiled with pcre2_compile_16(), you must do so with
pcre2_match_16(), not pcre2_match_8() or pcre2_match_32().
In the function summaries above, and in the rest of this document and
other PCRE2 documents, functions and data types are described using
their generic names, without the _8, _16, or _32 suffix.
PCRE2 API OVERVIEW
PCRE2 has its own native API, which is described in this document.
There are also some wrapper functions for the 8-bit library that corre‐
spond to the POSIX regular expression API, but they do not give access
to all the functionality of PCRE2. They are described in the pcre2posix
documentation. Both these APIs define a set of C function calls.
The native API C data types, function prototypes, option values, and
error codes are defined in the header file pcre2.h, which also contains
definitions of PCRE2_MAJOR and PCRE2_MINOR, the major and minor release
numbers for the library. Applications can use these to include support
for different releases of PCRE2.
In a Windows environment, if you want to statically link an application
program against a non-dll PCRE2 library, you must define PCRE2_STATIC
before including pcre2.h.
The functions pcre2_compile() and pcre2_match() are used for compiling
and matching regular expressions in a Perl-compatible manner. A sample
program that demonstrates the simplest way of using them is provided in
the file called pcre2demo.c in the PCRE2 source distribution. A listing
of this program is given in the pcre2demo documentation, and the
pcre2sample documentation describes how to compile and run it.
The compiling and matching functions recognize various options that are
passed as bits in an options argument. There are also some more compli‐
cated parameters such as custom memory management functions and
resource limits that are passed in "contexts" (which are just memory
blocks, described below). Simple applications do not need to make use
of contexts.
Just-in-time (JIT) compiler support is an optional feature of PCRE2
that can be built in appropriate hardware environments. It greatly
speeds up the matching performance of many patterns. Programs can
request that it be used if available by calling pcre2_jit_compile()
after a pattern has been successfully compiled by pcre2_compile(). This
does nothing if JIT support is not available.
More complicated programs might need to make use of the specialist
functions pcre2_jit_stack_create(), pcre2_jit_stack_free(), and
pcre2_jit_stack_assign() in order to control the JIT code's memory
usage.
JIT matching is automatically used by pcre2_match() if it is available,
unless the PCRE2_NO_JIT option is set. There is also a direct interface
for JIT matching, which gives improved performance at the expense of
less sanity checking. The JIT-specific functions are discussed in the
pcre2jit documentation.
A second matching function, pcre2_dfa_match(), which is not Perl-com‐
patible, is also provided. This uses a different algorithm for the
matching. The alternative algorithm finds all possible matches (at a
given point in the subject), and scans the subject just once (unless
there are lookaround assertions). However, this algorithm does not
return captured substrings. A description of the two matching algo‐
rithms and their advantages and disadvantages is given in the
pcre2matching documentation. There is no JIT support for
pcre2_dfa_match().
In addition to the main compiling and matching functions, there are
convenience functions for extracting captured substrings from a subject
string that has been matched by pcre2_match(). They are:
pcre2_substring_copy_byname()
pcre2_substring_copy_bynumber()
pcre2_substring_get_byname()
pcre2_substring_get_bynumber()
pcre2_substring_list_get()
pcre2_substring_length_byname()
pcre2_substring_length_bynumber()
pcre2_substring_nametable_scan()
pcre2_substring_number_from_name()
pcre2_substring_free() and pcre2_substring_list_free() are also pro‐
vided, to free memory used for extracted strings. If either of these
functions is called with a NULL argument, the function returns immedi‐
ately without doing anything.
The function pcre2_substitute() can be called to match a pattern and
return a copy of the subject string with substitutions for parts that
were matched.
Functions whose names begin with pcre2_serialize_ are used for saving
compiled patterns on disc or elsewhere, and reloading them later.
Finally, there are functions for finding out information about a com‐
piled pattern (pcre2_pattern_info()) and about the configuration with
which PCRE2 was built (pcre2_config()).
Functions with names ending with _free() are used for freeing memory
blocks of various sorts. In all cases, if one of these functions is
called with a NULL argument, it does nothing.
STRING LENGTHS AND OFFSETS
The PCRE2 API uses string lengths and offsets into strings of code
units in several places. These values are always of type PCRE2_SIZE,
which is an unsigned integer type, currently always defined as size_t.
The largest value that can be stored in such a type (that is
~(PCRE2_SIZE)0) is reserved as a special indicator for zero-terminated
strings and unset offsets. Therefore, the longest string that can be
handled is one less than this maximum.
NEWLINES
PCRE2 supports five different conventions for indicating line breaks in
strings: a single CR (carriage return) character, a single LF (line‐
feed) character, the two-character sequence CRLF, any of the three pre‐
ceding, or any Unicode newline sequence. The Unicode newline sequences
are the three just mentioned, plus the single characters VT (vertical
tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line
separator, U+2028), and PS (paragraph separator, U+2029).
Each of the first three conventions is used by at least one operating
system as its standard newline sequence. When PCRE2 is built, a default
can be specified. If it is not, the default is set to LF, which is the
Unix standard. However, the newline convention can be changed by an
application when calling pcre2_compile(), or it can be specified by
special text at the start of the pattern itself; this overrides any
other settings. See the pcre2pattern page for details of the special
character sequences.
In the PCRE2 documentation the word "newline" is used to mean "the
character or pair of characters that indicate a line break". The choice
of newline convention affects the handling of the dot, circumflex, and
dollar metacharacters, the handling of #-comments in /x mode, and, when
CRLF is a recognized line ending sequence, the match position advance‐
ment for a non-anchored pattern. There is more detail about this in the
section on pcre2_match() options below.
The choice of newline convention does not affect the interpretation of
the \n or \r escape sequences, nor does it affect what \R matches; this
has its own separate convention.
MULTITHREADING
In a multithreaded application it is important to keep thread-specific
data separate from data that can be shared between threads. The PCRE2
library code itself is thread-safe: it contains no static or global
variables. The API is designed to be fairly simple for non-threaded
applications while at the same time ensuring that multithreaded appli‐
cations can use it.
There are several different blocks of data that are used to pass infor‐
mation between the application and the PCRE2 libraries.
The compiled pattern
A pointer to the compiled form of a pattern is returned to the user
when pcre2_compile() is successful. The data in the compiled pattern is
fixed, and does not change when the pattern is matched. Therefore, it
is thread-safe, that is, the same compiled pattern can be used by more
than one thread simultaneously. For example, an application can compile
all its patterns at the start, before forking off multiple threads that
use them. However, if the just-in-time (JIT) optimization feature is
being used, it needs separate memory stack areas for each thread. See
the pcre2jit documentation for more details.
In a more complicated situation, where patterns are compiled only when
they are first needed, but are still shared between threads, pointers
to compiled patterns must be protected from simultaneous writing by
multiple threads, at least until a pattern has been compiled. The logic
can be something like this:
Get a read-only (shared) lock (mutex) for pointer
if (pointer == NULL)
{
Get a write (unique) lock for pointer
pointer = pcre2_compile(...
}
Release the lock
Use pointer in pcre2_match()
Of course, testing for compilation errors should also be included in
the code.
If JIT is being used, but the JIT compilation is not being done immedi‐
ately, (perhaps waiting to see if the pattern is used often enough)
similar logic is required. JIT compilation updates a pointer within the
compiled code block, so a thread must gain unique write access to the
pointer before calling pcre2_jit_compile(). Alternatively,
pcre2_code_copy() or pcre2_code_copy_with_tables() can be used to
obtain a private copy of the compiled code before calling the JIT com‐
piler.
Context blocks
The next main section below introduces the idea of "contexts" in which
PCRE2 functions are called. A context is nothing more than a collection
of parameters that control the way PCRE2 operates. Grouping a number of
parameters together in a context is a convenient way of passing them to
a PCRE2 function without using lots of arguments. The parameters that
are stored in contexts are in some sense "advanced features" of the
API. Many straightforward applications will not need to use contexts.
In a multithreaded application, if the parameters in a context are val‐
ues that are never changed, the same context can be used by all the
threads. However, if any thread needs to change any value in a context,
it must make its own thread-specific copy.
Match blocks
The matching functions need a block of memory for storing the results
of a match. This includes details of what was matched, as well as addi‐
tional information such as the name of a (*MARK) setting. Each thread
must provide its own copy of this memory.
PCRE2 CONTEXTS
Some PCRE2 functions have a lot of parameters, many of which are used
only by specialist applications, for example, those that use custom
memory management or non-standard character tables. To keep function
argument lists at a reasonable size, and at the same time to keep the
API extensible, "uncommon" parameters are passed to certain functions
in a context instead of directly. A context is just a block of memory
that holds the parameter values. Applications that do not need to
adjust any of the context parameters can pass NULL when a context
pointer is required.
There are three different types of context: a general context that is
relevant for several PCRE2 operations, a compile-time context, and a
match-time context.
The general context
At present, this context just contains pointers to (and data for)
external memory management functions that are called from several
places in the PCRE2 library. The context is named `general' rather than
specifically `memory' because in future other fields may be added. If
you do not want to supply your own custom memory management functions,
you do not need to bother with a general context. A general context is
created by:
pcre2_general_context *pcre2_general_context_create(
void *(*private_malloc)(PCRE2_SIZE, void *),
void (*private_free)(void *, void *), void *memory_data);
The two function pointers specify custom memory management functions,
whose prototypes are:
void *private_malloc(PCRE2_SIZE, void *);
void private_free(void *, void *);
Whenever code in PCRE2 calls these functions, the final argument is the
value of memory_data. Either of the first two arguments of the creation
function may be NULL, in which case the system memory management func‐
tions malloc() and free() are used. (This is not currently useful, as
there are no other fields in a general context, but in future there
might be.) The private_malloc() function is used (if supplied) to
obtain memory for storing the context, and all three values are saved
as part of the context.
Whenever PCRE2 creates a data block of any kind, the block contains a
pointer to the free() function that matches the malloc() function that
was used. When the time comes to free the block, this function is
called.
A general context can be copied by calling:
pcre2_general_context *pcre2_general_context_copy(
pcre2_general_context *gcontext);
The memory used for a general context should be freed by calling:
void pcre2_general_context_free(pcre2_general_context *gcontext);
If this function is passed a NULL argument, it returns immediately
without doing anything.
The compile context
A compile context is required if you want to provide an external func‐
tion for stack checking during compilation or to change the default
values of any of the following compile-time parameters:
What \R matches (Unicode newlines or CR, LF, CRLF only)
PCRE2's character tables
The newline character sequence
The compile time nested parentheses limit
The maximum length of the pattern string
The extra options bits (none set by default)
A compile context is also required if you are using custom memory man‐
agement. If none of these apply, just pass NULL as the context argu‐
ment of pcre2_compile().
A compile context is created, copied, and freed by the following func‐
tions:
pcre2_compile_context *pcre2_compile_context_create(
pcre2_general_context *gcontext);
pcre2_compile_context *pcre2_compile_context_copy(
pcre2_compile_context *ccontext);
void pcre2_compile_context_free(pcre2_compile_context *ccontext);
A compile context is created with default values for its parameters.
These can be changed by calling the following functions, which return 0
on success, or PCRE2_ERROR_BADDATA if invalid data is detected.
int pcre2_set_bsr(pcre2_compile_context *ccontext,
uint32_t value);
The value must be PCRE2_BSR_ANYCRLF, to specify that \R matches only
CR, LF, or CRLF, or PCRE2_BSR_UNICODE, to specify that \R matches any
Unicode line ending sequence. The value is used by the JIT compiler and
by the two interpreted matching functions, pcre2_match() and
pcre2_dfa_match().
int pcre2_set_character_tables(pcre2_compile_context *ccontext,
const unsigned char *tables);
The value must be the result of a call to pcre2_maketables(), whose
only argument is a general context. This function builds a set of char‐
acter tables in the current locale.
int pcre2_set_compile_extra_options(pcre2_compile_context *ccontext,
uint32_t extra_options);
As PCRE2 has developed, almost all the 32 option bits that are avail‐
able in the options argument of pcre2_compile() have been used up. To
avoid running out, the compile context contains a set of extra option
bits which are used for some newer, assumed rarer, options. This func‐
tion sets those bits. It always sets all the bits (either on or off).
It does not modify any existing setting. The available options are
defined in the section entitled "Extra compile options" below.
int pcre2_set_max_pattern_length(pcre2_compile_context *ccontext,
PCRE2_SIZE value);
This sets a maximum length, in code units, for any pattern string that
is compiled with this context. If the pattern is longer, an error is
generated. This facility is provided so that applications that accept
patterns from external sources can limit their size. The default is the
largest number that a PCRE2_SIZE variable can hold, which is effec‐
tively unlimited.
int pcre2_set_newline(pcre2_compile_context *ccontext,
uint32_t value);
This specifies which characters or character sequences are to be recog‐
nized as newlines. The value must be one of PCRE2_NEWLINE_CR (carriage
return only), PCRE2_NEWLINE_LF (linefeed only), PCRE2_NEWLINE_CRLF (the
two-character sequence CR followed by LF), PCRE2_NEWLINE_ANYCRLF (any
of the above), PCRE2_NEWLINE_ANY (any Unicode newline sequence), or
PCRE2_NEWLINE_NUL (the NUL character, that is a binary zero).
A pattern can override the value set in the compile context by starting
with a sequence such as (*CRLF). See the pcre2pattern page for details.
When a pattern is compiled with the PCRE2_EXTENDED or
PCRE2_EXTENDED_MORE option, the newline convention affects the recogni‐
tion of the end of internal comments starting with #. The value is
saved with the compiled pattern for subsequent use by the JIT compiler
and by the two interpreted matching functions, pcre2_match() and
pcre2_dfa_match().
int pcre2_set_parens_nest_limit(pcre2_compile_context *ccontext,
uint32_t value);
This parameter ajusts the limit, set when PCRE2 is built (default 250),
on the depth of parenthesis nesting in a pattern. This limit stops
rogue patterns using up too much system stack when being compiled. The
limit applies to parentheses of all kinds, not just capturing parenthe‐
ses.
int pcre2_set_compile_recursion_guard(pcre2_compile_context *ccontext,
int (*guard_function)(uint32_t, void *), void *user_data);
There is at least one application that runs PCRE2 in threads with very
limited system stack, where running out of stack is to be avoided at
all costs. The parenthesis limit above cannot take account of how much
stack is actually available during compilation. For a finer control,
you can supply a function that is called whenever pcre2_compile()
starts to compile a parenthesized part of a pattern. This function can
check the actual stack size (or anything else that it wants to, of
course).
The first argument to the callout function gives the current depth of
nesting, and the second is user data that is set up by the last argu‐
ment of pcre2_set_compile_recursion_guard(). The callout function
should return zero if all is well, or non-zero to force an error.
The match context
A match context is required if you want to:
Set up a callout function
Set an offset limit for matching an unanchored pattern
Change the limit on the amount of heap used when matching
Change the backtracking match limit
Change the backtracking depth limit
Set custom memory management specifically for the match
If none of these apply, just pass NULL as the context argument of
pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match().
A match context is created, copied, and freed by the following func‐
tions:
pcre2_match_context *pcre2_match_context_create(
pcre2_general_context *gcontext);
pcre2_match_context *pcre2_match_context_copy(
pcre2_match_context *mcontext);
void pcre2_match_context_free(pcre2_match_context *mcontext);
A match context is created with default values for its parameters.
These can be changed by calling the following functions, which return 0
on success, or PCRE2_ERROR_BADDATA if invalid data is detected.
int pcre2_set_callout(pcre2_match_context *mcontext,
int (*callout_function)(pcre2_callout_block *, void *),
void *callout_data);
This sets up a "callout" function for PCRE2 to call at specified points
during a matching operation. Details are given in the pcre2callout doc‐
umentation.
int pcre2_set_offset_limit(pcre2_match_context *mcontext,
PCRE2_SIZE value);
The offset_limit parameter limits how far an unanchored search can
advance in the subject string. The default value is PCRE2_UNSET. The
pcre2_match() and pcre2_dfa_match() functions return
PCRE2_ERROR_NOMATCH if a match with a starting point before or at the
given offset is not found. The pcre2_substitute() function makes no
more substitutions.
For example, if the pattern /abc/ is matched against "123abc" with an
offset limit less than 3, the result is PCRE2_ERROR_NO_MATCH. A match
can never be found if the startoffset argument of pcre2_match(),
pcre2_dfa_match(), or pcre2_substitute() is greater than the offset
limit set in the match context.
When using this facility, you must set the PCRE2_USE_OFFSET_LIMIT
option when calling pcre2_compile() so that when JIT is in use, differ‐
ent code can be compiled. If a match is started with a non-default
match limit when PCRE2_USE_OFFSET_LIMIT is not set, an error is gener‐
ated.
The offset limit facility can be used to track progress when searching
large subject strings or to limit the extent of global substitutions.
See also the PCRE2_FIRSTLINE option, which requires a match to start
before or at the first newline that follows the start of matching in
the subject. If this is set with an offset limit, a match must occur in
the first line and also within the offset limit. In other words, which‐
ever limit comes first is used.
int pcre2_set_heap_limit(pcre2_match_context *mcontext,
uint32_t value);
The heap_limit parameter specifies, in units of kibibytes (1024 bytes),
the maximum amount of heap memory that pcre2_match() may use to hold
backtracking information when running an interpretive match. This limit
also applies to pcre2_dfa_match(), which may use the heap when process‐
ing patterns with a lot of nested pattern recursion or lookarounds or
atomic groups. This limit does not apply to matching with the JIT opti‐
mization, which has its own memory control arrangements (see the
pcre2jit documentation for more details). If the limit is reached, the
negative error code PCRE2_ERROR_HEAPLIMIT is returned. The default
limit can be set when PCRE2 is built; if it is not, the default is set
very large and is essentially "unlimited".
A value for the heap limit may also be supplied by an item at the start
of a pattern of the form
(*LIMIT_HEAP=ddd)
where ddd is a decimal number. However, such a setting is ignored
unless ddd is less than the limit set by the caller of pcre2_match()
or, if no such limit is set, less than the default.
The pcre2_match() function starts out using a 20KiB vector on the sys‐
tem stack for recording backtracking points. The more nested backtrack‐
ing points there are (that is, the deeper the search tree), the more
memory is needed. Heap memory is used only if the initial vector is
too small. If the heap limit is set to a value less than 21 (in partic‐
ular, zero) no heap memory will be used. In this case, only patterns
that do not have a lot of nested backtracking can be successfully pro‐
cessed.
Similarly, for pcre2_dfa_match(), a vector on the system stack is used
when processing pattern recursions, lookarounds, or atomic groups, and
only if this is not big enough is heap memory used. In this case, too,
setting a value of zero disables the use of the heap.
int pcre2_set_match_limit(pcre2_match_context *mcontext,
uint32_t value);
The match_limit parameter provides a means of preventing PCRE2 from
using up too many computing resources when processing patterns that are
not going to match, but which have a very large number of possibilities
in their search trees. The classic example is a pattern that uses
nested unlimited repeats.
There is an internal counter in pcre2_match() that is incremented each
time round its main matching loop. If this value reaches the match
limit, pcre2_match() returns the negative value PCRE2_ERROR_MATCHLIMIT.
This has the effect of limiting the amount of backtracking that can
take place. For patterns that are not anchored, the count restarts from
zero for each position in the subject string. This limit also applies
to pcre2_dfa_match(), though the counting is done in a different way.
When pcre2_match() is called with a pattern that was successfully pro‐
cessed by pcre2_jit_compile(), the way in which matching is executed is
entirely different. However, there is still the possibility of runaway
matching that goes on for a very long time, and so the match_limit
value is also used in this case (but in a different way) to limit how
long the matching can continue.
The default value for the limit can be set when PCRE2 is built; the
default default is 10 million, which handles all but the most extreme
cases. A value for the match limit may also be supplied by an item at
the start of a pattern of the form
(*LIMIT_MATCH=ddd)
where ddd is a decimal number. However, such a setting is ignored
unless ddd is less than the limit set by the caller of pcre2_match() or
pcre2_dfa_match() or, if no such limit is set, less than the default.
int pcre2_set_depth_limit(pcre2_match_context *mcontext,
uint32_t value);
This parameter limits the depth of nested backtracking in
pcre2_match(). Each time a nested backtracking point is passed, a new
memory "frame" is used to remember the state of matching at that point.
Thus, this parameter indirectly limits the amount of memory that is
used in a match. However, because the size of each memory "frame"
depends on the number of capturing parentheses, the actual memory limit
varies from pattern to pattern. This limit was more useful in versions
before 10.30, where function recursion was used for backtracking.
The depth limit is not relevant, and is ignored, when matching is done
using JIT compiled code. However, it is supported by pcre2_dfa_match(),
which uses it to limit the depth of nested internal recursive function
calls that implement atomic groups, lookaround assertions, and pattern
recursions. This limits, indirectly, the amount of system stack that is
used. It was more useful in versions before 10.32, when stack memory
was used for local workspace vectors for recursive function calls. From
version 10.32, only local variables are allocated on the stack and as
each call uses only a few hundred bytes, even a small stack can support
quite a lot of recursion.
If the depth of internal recursive function calls is great enough,
local workspace vectors are allocated on the heap from version 10.32
onwards, so the depth limit also indirectly limits the amount of heap
memory that is used. A recursive pattern such as /(.(?2))((?1)|)/, when
matched to a very long string using pcre2_dfa_match(), can use a great
deal of memory. However, it is probably better to limit heap usage
directly by calling pcre2_set_heap_limit().
The default value for the depth limit can be set when PCRE2 is built;
if it is not, the default is set to the same value as the default for
the match limit. If the limit is exceeded, pcre2_match() or
pcre2_dfa_match() returns PCRE2_ERROR_DEPTHLIMIT. A value for the depth
limit may also be supplied by an item at the start of a pattern of the
form
(*LIMIT_DEPTH=ddd)
where ddd is a decimal number. However, such a setting is ignored
unless ddd is less than the limit set by the caller of pcre2_match() or
pcre2_dfa_match() or, if no such limit is set, less than the default.
CHECKING BUILD-TIME OPTIONS
int pcre2_config(uint32_t what, void *where);
The function pcre2_config() makes it possible for a PCRE2 client to
discover which optional features have been compiled into the PCRE2
library. The pcre2build documentation has more details about these
optional features.
The first argument for pcre2_config() specifies which information is
required. The second argument is a pointer to memory into which the
information is placed. If NULL is passed, the function returns the
amount of memory that is needed for the requested information. For
calls that return numerical values, the value is in bytes; when
requesting these values, where should point to appropriately aligned
memory. For calls that return strings, the required length is given in
code units, not counting the terminating zero.
When requesting information, the returned value from pcre2_config() is
non-negative on success, or the negative error code PCRE2_ERROR_BADOP‐
TION if the value in the first argument is not recognized. The follow‐
ing information is available:
PCRE2_CONFIG_BSR
The output is a uint32_t integer whose value indicates what character
sequences the \R escape sequence matches by default. A value of
PCRE2_BSR_UNICODE means that \R matches any Unicode line ending
sequence; a value of PCRE2_BSR_ANYCRLF means that \R matches only CR,
LF, or CRLF. The default can be overridden when a pattern is compiled.
PCRE2_CONFIG_COMPILED_WIDTHS
The output is a uint32_t integer whose lower bits indicate which code
unit widths were selected when PCRE2 was built. The 1-bit indicates
8-bit support, and the 2-bit and 4-bit indicate 16-bit and 32-bit sup‐
port, respectively.
PCRE2_CONFIG_DEPTHLIMIT
The output is a uint32_t integer that gives the default limit for the
depth of nested backtracking in pcre2_match() or the depth of nested
recursions, lookarounds, and atomic groups in pcre2_dfa_match(). Fur‐
ther details are given with pcre2_set_depth_limit() above.
PCRE2_CONFIG_HEAPLIMIT
The output is a uint32_t integer that gives, in kibibytes, the default
limit for the amount of heap memory used by pcre2_match() or
pcre2_dfa_match(). Further details are given with
pcre2_set_heap_limit() above.
PCRE2_CONFIG_JIT
The output is a uint32_t integer that is set to one if support for
just-in-time compiling is available; otherwise it is set to zero.
PCRE2_CONFIG_JITTARGET
The where argument should point to a buffer that is at least 48 code
units long. (The exact length required can be found by calling
pcre2_config() with where set to NULL.) The buffer is filled with a
string that contains the name of the architecture for which the JIT
compiler is configured, for example "x86 32bit (little endian +
unaligned)". If JIT support is not available, PCRE2_ERROR_BADOPTION is
returned, otherwise the number of code units used is returned. This is
the length of the string, plus one unit for the terminating zero.
PCRE2_CONFIG_LINKSIZE
The output is a uint32_t integer that contains the number of bytes used
for internal linkage in compiled regular expressions. When PCRE2 is
configured, the value can be set to 2, 3, or 4, with the default being
2. This is the value that is returned by pcre2_config(). However, when
the 16-bit library is compiled, a value of 3 is rounded up to 4, and
when the 32-bit library is compiled, internal linkages always use 4
bytes, so the configured value is not relevant.
The default value of 2 for the 8-bit and 16-bit libraries is sufficient
for all but the most massive patterns, since it allows the size of the
compiled pattern to be up to 65535 code units. Larger values allow
larger regular expressions to be compiled by those two libraries, but
at the expense of slower matching.
PCRE2_CONFIG_MATCHLIMIT
The output is a uint32_t integer that gives the default match limit for
pcre2_match(). Further details are given with pcre2_set_match_limit()
above.
PCRE2_CONFIG_NEWLINE
The output is a uint32_t integer whose value specifies the default
character sequence that is recognized as meaning "newline". The values
are:
PCRE2_NEWLINE_CR Carriage return (CR)
PCRE2_NEWLINE_LF Linefeed (LF)
PCRE2_NEWLINE_CRLF Carriage return, linefeed (CRLF)
PCRE2_NEWLINE_ANY Any Unicode line ending
PCRE2_NEWLINE_ANYCRLF Any of CR, LF, or CRLF
PCRE2_NEWLINE_NUL The NUL character (binary zero)
The default should normally correspond to the standard sequence for
your operating system.
PCRE2_CONFIG_NEVER_BACKSLASH_C
The output is a uint32_t integer that is set to one if the use of \C
was permanently disabled when PCRE2 was built; otherwise it is set to
zero.
PCRE2_CONFIG_PARENSLIMIT
The output is a uint32_t integer that gives the maximum depth of nest‐
ing of parentheses (of any kind) in a pattern. This limit is imposed to
cap the amount of system stack used when a pattern is compiled. It is
specified when PCRE2 is built; the default is 250. This limit does not
take into account the stack that may already be used by the calling
application. For finer control over compilation stack usage, see
pcre2_set_compile_recursion_guard().
PCRE2_CONFIG_STACKRECURSE
This parameter is obsolete and should not be used in new code. The out‐
put is a uint32_t integer that is always set to zero.
PCRE2_CONFIG_UNICODE_VERSION
The where argument should point to a buffer that is at least 24 code
units long. (The exact length required can be found by calling
pcre2_config() with where set to NULL.) If PCRE2 has been compiled
without Unicode support, the buffer is filled with the text "Unicode
not supported". Otherwise, the Unicode version string (for example,
"8.0.0") is inserted. The number of code units used is returned. This
is the length of the string plus one unit for the terminating zero.
PCRE2_CONFIG_UNICODE
The output is a uint32_t integer that is set to one if Unicode support
is available; otherwise it is set to zero. Unicode support implies UTF
support.
PCRE2_CONFIG_VERSION
The where argument should point to a buffer that is at least 24 code
units long. (The exact length required can be found by calling
pcre2_config() with where set to NULL.) The buffer is filled with the
PCRE2 version string, zero-terminated. The number of code units used is
returned. This is the length of the string plus one unit for the termi‐
nating zero.
COMPILING A PATTERN
pcre2_code *pcre2_compile(PCRE2_SPTR pattern, PCRE2_SIZE length,
uint32_t options, int *errorcode, PCRE2_SIZE *erroroffset,
pcre2_compile_context *ccontext);
void pcre2_code_free(pcre2_code *code);
pcre2_code *pcre2_code_copy(const pcre2_code *code);
pcre2_code *pcre2_code_copy_with_tables(const pcre2_code *code);
The pcre2_compile() function compiles a pattern into an internal form.
The pattern is defined by a pointer to a string of code units and a
length (in code units). If the pattern is zero-terminated, the length
can be specified as PCRE2_ZERO_TERMINATED. The function returns a
pointer to a block of memory that contains the compiled pattern and
related data, or NULL if an error occurred.
If the compile context argument ccontext is NULL, memory for the com‐
piled pattern is obtained by calling malloc(). Otherwise, it is
obtained from the same memory function that was used for the compile
context. The caller must free the memory by calling pcre2_code_free()
when it is no longer needed. If pcre2_code_free() is called with a
NULL argument, it returns immediately, without doing anything.
The function pcre2_code_copy() makes a copy of the compiled code in new
memory, using the same memory allocator as was used for the original.
However, if the code has been processed by the JIT compiler (see
below), the JIT information cannot be copied (because it is position-
dependent). The new copy can initially be used only for non-JIT match‐
ing, though it can be passed to pcre2_jit_compile() if required. If
pcre2_code_copy() is called with a NULL argument, it returns NULL.
The pcre2_code_copy() function provides a way for individual threads in
a multithreaded application to acquire a private copy of shared com‐
piled code. However, it does not make a copy of the character tables
used by the compiled pattern; the new pattern code points to the same
tables as the original code. (See "Locale Support" below for details
of these character tables.) In many applications the same tables are
used throughout, so this behaviour is appropriate. Nevertheless, there
are occasions when a copy of a compiled pattern and the relevant tables
are needed. The pcre2_code_copy_with_tables() provides this facility.
Copies of both the code and the tables are made, with the new code
pointing to the new tables. The memory for the new tables is automati‐
cally freed when pcre2_code_free() is called for the new copy of the
compiled code. If pcre2_code_copy_withy_tables() is called with a NULL
argument, it returns NULL.
NOTE: When one of the matching functions is called, pointers to the
compiled pattern and the subject string are set in the match data block
so that they can be referenced by the substring extraction functions.
After running a match, you must not free a compiled pattern (or a sub‐
ject string) until after all operations on the match data block have
taken place.
The options argument for pcre2_compile() contains various bit settings
that affect the compilation. It should be zero if no options are
required. The available options are described below. Some of them (in
particular, those that are compatible with Perl, but some others as
well) can also be set and unset from within the pattern (see the
detailed description in the pcre2pattern documentation).
For those options that can be different in different parts of the pat‐
tern, the contents of the options argument specifies their settings at
the start of compilation. The PCRE2_ANCHORED, PCRE2_ENDANCHORED, and
PCRE2_NO_UTF_CHECK options can be set at the time of matching as well
as at compile time.
Other, less frequently required compile-time parameters (for example,
the newline setting) can be provided in a compile context (as described
above).
If errorcode or erroroffset is NULL, pcre2_compile() returns NULL imme‐
diately. Otherwise, the variables to which these point are set to an
error code and an offset (number of code units) within the pattern,
respectively, when pcre2_compile() returns NULL because a compilation
error has occurred. The values are not defined when compilation is suc‐
cessful and pcre2_compile() returns a non-NULL value.
There are nearly 100 positive error codes that pcre2_compile() may
return if it finds an error in the pattern. There are also some nega‐
tive error codes that are used for invalid UTF strings. These are the
same as given by pcre2_match() and pcre2_dfa_match(), and are described
in the pcre2unicode page. There is no separate documentation for the
positive error codes, because the textual error messages that are
obtained by calling the pcre2_get_error_message() function (see
"Obtaining a textual error message" below) should be self-explanatory.
Macro names starting with PCRE2_ERROR_ are defined for both positive
and negative error codes in pcre2.h.
The value returned in erroroffset is an indication of where in the pat‐
tern the error occurred. It is not necessarily the furthest point in
the pattern that was read. For example, after the error "lookbehind
assertion is not fixed length", the error offset points to the start of
the failing assertion. For an invalid UTF-8 or UTF-16 string, the off‐
set is that of the first code unit of the failing character.
Some errors are not detected until the whole pattern has been scanned;
in these cases, the offset passed back is the length of the pattern.
Note that the offset is in code units, not characters, even in a UTF
mode. It may sometimes point into the middle of a UTF-8 or UTF-16 char‐
acter.
This code fragment shows a typical straightforward call to pcre2_com‐
pile():
pcre2_code *re;
PCRE2_SIZE erroffset;
int errorcode;
re = pcre2_compile(
"^A.*Z", /* the pattern */
PCRE2_ZERO_TERMINATED, /* the pattern is zero-terminated */
0, /* default options */
&errorcode, /* for error code */
&erroffset, /* for error offset */
NULL); /* no compile context */
The following names for option bits are defined in the pcre2.h header
file:
PCRE2_ANCHORED
If this bit is set, the pattern is forced to be "anchored", that is, it
is constrained to match only at the first matching point in the string
that is being searched (the "subject string"). This effect can also be
achieved by appropriate constructs in the pattern itself, which is the
only way to do it in Perl.
PCRE2_ALLOW_EMPTY_CLASS
By default, for compatibility with Perl, a closing square bracket that
immediately follows an opening one is treated as a data character for
the class. When PCRE2_ALLOW_EMPTY_CLASS is set, it terminates the
class, which therefore contains no characters and so can never match.
PCRE2_ALT_BSUX
This option request alternative handling of three escape sequences,
which makes PCRE2's behaviour more like ECMAscript (aka JavaScript).
When it is set:
(1) \U matches an upper case "U" character; by default \U causes a com‐
pile time error (Perl uses \U to upper case subsequent characters).
(2) \u matches a lower case "u" character unless it is followed by four
hexadecimal digits, in which case the hexadecimal number defines the
code point to match. By default, \u causes a compile time error (Perl
uses it to upper case the following character).
(3) \x matches a lower case "x" character unless it is followed by two
hexadecimal digits, in which case the hexadecimal number defines the
code point to match. By default, as in Perl, a hexadecimal number is
always expected after \x, but it may have zero, one, or two digits (so,
for example, \xz matches a binary zero character followed by z).
PCRE2_ALT_CIRCUMFLEX
In multiline mode (when PCRE2_MULTILINE is set), the circumflex
metacharacter matches at the start of the subject (unless PCRE2_NOTBOL
is set), and also after any internal newline. However, it does not
match after a newline at the end of the subject, for compatibility with
Perl. If you want a multiline circumflex also to match after a termi‐
nating newline, you must set PCRE2_ALT_CIRCUMFLEX.
PCRE2_ALT_VERBNAMES
By default, for compatibility with Perl, the name in any verb sequence
such as (*MARK:NAME) is any sequence of characters that does not
include a closing parenthesis. The name is not processed in any way,
and it is not possible to include a closing parenthesis in the name.
However, if the PCRE2_ALT_VERBNAMES option is set, normal backslash
processing is applied to verb names and only an unescaped closing
parenthesis terminates the name. A closing parenthesis can be included
in a name either as \) or between \Q and \E. If the PCRE2_EXTENDED or
PCRE2_EXTENDED_MORE option is set with PCRE2_ALT_VERBNAMES, unescaped
whitespace in verb names is skipped and #-comments are recognized,
exactly as in the rest of the pattern.
PCRE2_AUTO_CALLOUT
If this bit is set, pcre2_compile() automatically inserts callout
items, all with number 255, before each pattern item, except immedi‐
ately before or after an explicit callout in the pattern. For discus‐
sion of the callout facility, see the pcre2callout documentation.
PCRE2_CASELESS
If this bit is set, letters in the pattern match both upper and lower
case letters in the subject. It is equivalent to Perl's /i option, and
it can be changed within a pattern by a (?i) option setting. If
PCRE2_UTF is set, Unicode properties are used for all characters with
more than one other case, and for all characters whose code points are
greater than U+007F. For lower valued characters with only one other
case, a lookup table is used for speed. When PCRE2_UTF is not set, a
lookup table is used for all code points less than 256, and higher code
points (available only in 16-bit or 32-bit mode) are treated as not
having another case.
PCRE2_DOLLAR_ENDONLY
If this bit is set, a dollar metacharacter in the pattern matches only
at the end of the subject string. Without this option, a dollar also
matches immediately before a newline at the end of the string (but not
before any other newlines). The PCRE2_DOLLAR_ENDONLY option is ignored
if PCRE2_MULTILINE is set. There is no equivalent to this option in
Perl, and no way to set it within a pattern.
PCRE2_DOTALL
If this bit is set, a dot metacharacter in the pattern matches any
character, including one that indicates a newline. However, it only
ever matches one character, even if newlines are coded as CRLF. Without
this option, a dot does not match when the current position in the sub‐
ject is at a newline. This option is equivalent to Perl's /s option,
and it can be changed within a pattern by a (?s) option setting. A neg‐
ative class such as [^a] always matches newline characters, and the \N
escape sequence always matches a non-newline character, independent of
the setting of PCRE2_DOTALL.
PCRE2_DUPNAMES
If this bit is set, names used to identify capturing subpatterns need
not be unique. This can be helpful for certain types of pattern when it
is known that only one instance of the named subpattern can ever be
matched. There are more details of named subpatterns below; see also
the pcre2pattern documentation.
PCRE2_ENDANCHORED
If this bit is set, the end of any pattern match must be right at the
end of the string being searched (the "subject string"). If the pattern
match succeeds by reaching (*ACCEPT), but does not reach the end of the
subject, the match fails at the current starting point. For unanchored
patterns, a new match is then tried at the next starting point. How‐
ever, if the match succeeds by reaching the end of the pattern, but not
the end of the subject, backtracking occurs and an alternative match
may be found. Consider these two patterns:
.(*ACCEPT)|..
.|..
If matched against "abc" with PCRE2_ENDANCHORED set, the first matches
"c" whereas the second matches "bc". The effect of PCRE2_ENDANCHORED
can also be achieved by appropriate constructs in the pattern itself,
which is the only way to do it in Perl.
For DFA matching with pcre2_dfa_match(), PCRE2_ENDANCHORED applies only
to the first (that is, the longest) matched string. Other parallel
matches, which are necessarily substrings of the first one, must obvi‐
ously end before the end of the subject.
PCRE2_EXTENDED
If this bit is set, most white space characters in the pattern are
totally ignored except when escaped or inside a character class. How‐
ever, white space is not allowed within sequences such as (?> that
introduce various parenthesized subpatterns, nor within numerical quan‐
tifiers such as {1,3}. Ignorable white space is permitted between an
item and a following quantifier and between a quantifier and a follow‐
ing + that indicates possessiveness. PCRE2_EXTENDED is equivalent to
Perl's /x option, and it can be changed within a pattern by a (?x)
option setting.
When PCRE2 is compiled without Unicode support, PCRE2_EXTENDED recog‐
nizes as white space only those characters with code points less than
256 that are flagged as white space in its low-character table. The ta‐
ble is normally created by pcre2_maketables(), which uses the isspace()
function to identify space characters. In most ASCII environments, the
relevant characters are those with code points 0x0009 (tab), 0x000A
(linefeed), 0x000B (vertical tab), 0x000C (formfeed), 0x000D (carriage
return), and 0x0020 (space).
When PCRE2 is compiled with Unicode support, in addition to these char‐
acters, five more Unicode "Pattern White Space" characters are recog‐
nized by PCRE2_EXTENDED. These are U+0085 (next line), U+200E (left-to-
right mark), U+200F (right-to-left mark), U+2028 (line separator), and
U+2029 (paragraph separator). This set of characters is the same as
recognized by Perl's /x option. Note that the horizontal and vertical
space characters that are matched by the \h and \v escapes in patterns
are a much bigger set.
As well as ignoring most white space, PCRE2_EXTENDED also causes char‐
acters between an unescaped # outside a character class and the next
newline, inclusive, to be ignored, which makes it possible to include
comments inside complicated patterns. Note that the end of this type of
comment is a literal newline sequence in the pattern; escape sequences
that happen to represent a newline do not count.
Which characters are interpreted as newlines can be specified by a set‐
ting in the compile context that is passed to pcre2_compile() or by a
special sequence at the start of the pattern, as described in the sec‐
tion entitled "Newline conventions" in the pcre2pattern documentation.
A default is defined when PCRE2 is built.
PCRE2_EXTENDED_MORE
This option has the effect of PCRE2_EXTENDED, but, in addition,
unescaped space and horizontal tab characters are ignored inside a
character class. Note: only these two characters are ignored, not the
full set of pattern white space characters that are ignored outside a
character class. PCRE2_EXTENDED_MORE is equivalent to Perl's /xx
option, and it can be changed within a pattern by a (?xx) option set‐
ting.
PCRE2_FIRSTLINE
If this option is set, the start of an unanchored pattern match must be
before or at the first newline in the subject string following the
start of matching, though the matched text may continue over the new‐
line. If startoffset is non-zero, the limiting newline is not necessar‐
ily the first newline in the subject. For example, if the subject
string is "abc\nxyz" (where \n represents a single-character newline) a
pattern match for "yz" succeeds with PCRE2_FIRSTLINE if startoffset is
greater than 3. See also PCRE2_USE_OFFSET_LIMIT, which provides a more
general limiting facility. If PCRE2_FIRSTLINE is set with an offset
limit, a match must occur in the first line and also within the offset
limit. In other words, whichever limit comes first is used.
PCRE2_LITERAL
If this option is set, all meta-characters in the pattern are disabled,
and it is treated as a literal string. Matching literal strings with a
regular expression engine is not the most efficient way of doing it. If
you are doing a lot of literal matching and are worried about effi‐
ciency, you should consider using other approaches. The only other main
options that are allowed with PCRE2_LITERAL are: PCRE2_ANCHORED,
PCRE2_ENDANCHORED, PCRE2_AUTO_CALLOUT, PCRE2_CASELESS, PCRE2_FIRSTLINE,
PCRE2_NO_START_OPTIMIZE, PCRE2_NO_UTF_CHECK, PCRE2_UTF, and
PCRE2_USE_OFFSET_LIMIT. The extra options PCRE2_EXTRA_MATCH_LINE and
PCRE2_EXTRA_MATCH_WORD are also supported. Any other options cause an
error.
PCRE2_MATCH_UNSET_BACKREF
If this option is set, a backreference to an unset subpattern group
matches an empty string (by default this causes the current matching
alternative to fail). A pattern such as (\1)(a) succeeds when this
option is set (assuming it can find an "a" in the subject), whereas it
fails by default, for Perl compatibility. Setting this option makes
PCRE2 behave more like ECMAscript (aka JavaScript).
PCRE2_MULTILINE
By default, for the purposes of matching "start of line" and "end of
line", PCRE2 treats the subject string as consisting of a single line
of characters, even if it actually contains newlines. The "start of
line" metacharacter (^) matches only at the start of the string, and
the "end of line" metacharacter ($) matches only at the end of the
string, or before a terminating newline (except when PCRE2_DOL‐
LAR_ENDONLY is set). Note, however, that unless PCRE2_DOTALL is set,
the "any character" metacharacter (.) does not match at a newline. This
behaviour (for ^, $, and dot) is the same as Perl.
When PCRE2_MULTILINE it is set, the "start of line" and "end of line"
constructs match immediately following or immediately before internal
newlines in the subject string, respectively, as well as at the very
start and end. This is equivalent to Perl's /m option, and it can be
changed within a pattern by a (?m) option setting. Note that the "start
of line" metacharacter does not match after a newline at the end of the
subject, for compatibility with Perl. However, you can change this by
setting the PCRE2_ALT_CIRCUMFLEX option. If there are no newlines in a
subject string, or no occurrences of ^ or $ in a pattern, setting
PCRE2_MULTILINE has no effect.
PCRE2_NEVER_BACKSLASH_C
This option locks out the use of \C in the pattern that is being com‐
piled. This escape can cause unpredictable behaviour in UTF-8 or
UTF-16 modes, because it may leave the current matching point in the
middle of a multi-code-unit character. This option may be useful in
applications that process patterns from external sources. Note that
there is also a build-time option that permanently locks out the use of
\C.
PCRE2_NEVER_UCP
This option locks out the use of Unicode properties for handling \B,
\b, \D, \d, \S, \s, \W, \w, and some of the POSIX character classes, as
described for the PCRE2_UCP option below. In particular, it prevents
the creator of the pattern from enabling this facility by starting the
pattern with (*UCP). This option may be useful in applications that
process patterns from external sources. The option combination PCRE_UCP
and PCRE_NEVER_UCP causes an error.
PCRE2_NEVER_UTF
This option locks out interpretation of the pattern as UTF-8, UTF-16,
or UTF-32, depending on which library is in use. In particular, it pre‐
vents the creator of the pattern from switching to UTF interpretation
by starting the pattern with (*UTF). This option may be useful in
applications that process patterns from external sources. The combina‐
tion of PCRE2_UTF and PCRE2_NEVER_UTF causes an error.
PCRE2_NO_AUTO_CAPTURE
If this option is set, it disables the use of numbered capturing paren‐
theses in the pattern. Any opening parenthesis that is not followed by
? behaves as if it were followed by ?: but named parentheses can still
be used for capturing (and they acquire numbers in the usual way). This
is the same as Perl's /n option. Note that, when this option is set,
references to capturing groups (backreferences or recursion/subroutine
calls) may only refer to named groups, though the reference can be by
name or by number.
PCRE2_NO_AUTO_POSSESS
If this option is set, it disables "auto-possessification", which is an
optimization that, for example, turns a+b into a++b in order to avoid
backtracks into a+ that can never be successful. However, if callouts
are in use, auto-possessification means that some callouts are never
taken. You can set this option if you want the matching functions to do
a full unoptimized search and run all the callouts, but it is mainly
provided for testing purposes.
PCRE2_NO_DOTSTAR_ANCHOR
If this option is set, it disables an optimization that is applied when
.* is the first significant item in a top-level branch of a pattern,
and all the other branches also start with .* or with \A or \G or ^.
The optimization is automatically disabled for .* if it is inside an
atomic group or a capturing group that is the subject of a backrefer‐
ence, or if the pattern contains (*PRUNE) or (*SKIP). When the opti‐
mization is not disabled, such a pattern is automatically anchored if
PCRE2_DOTALL is set for all the .* items and PCRE2_MULTILINE is not set
for any ^ items. Otherwise, the fact that any match must start either
at the start of the subject or following a newline is remembered. Like
other optimizations, this can cause callouts to be skipped.
PCRE2_NO_START_OPTIMIZE
This is an option whose main effect is at matching time. It does not
change what pcre2_compile() generates, but it does affect the output of
the JIT compiler.
There are a number of optimizations that may occur at the start of a
match, in order to speed up the process. For example, if it is known
that an unanchored match must start with a specific code unit value,
the matching code searches the subject for that value, and fails imme‐
diately if it cannot find it, without actually running the main match‐
ing function. This means that a special item such as (*COMMIT) at the
start of a pattern is not considered until after a suitable starting
point for the match has been found. Also, when callouts or (*MARK)
items are in use, these "start-up" optimizations can cause them to be
skipped if the pattern is never actually used. The start-up optimiza‐
tions are in effect a pre-scan of the subject that takes place before
the pattern is run.
The PCRE2_NO_START_OPTIMIZE option disables the start-up optimizations,
possibly causing performance to suffer, but ensuring that in cases
where the result is "no match", the callouts do occur, and that items
such as (*COMMIT) and (*MARK) are considered at every possible starting
position in the subject string.
Setting PCRE2_NO_START_OPTIMIZE may change the outcome of a matching
operation. Consider the pattern
(*COMMIT)ABC
When this is compiled, PCRE2 records the fact that a match must start
with the character "A". Suppose the subject string is "DEFABC". The
start-up optimization scans along the subject, finds "A" and runs the
first match attempt from there. The (*COMMIT) item means that the pat‐
tern must match the current starting position, which in this case, it
does. However, if the same match is run with PCRE2_NO_START_OPTIMIZE
set, the initial scan along the subject string does not happen. The
first match attempt is run starting from "D" and when this fails,
(*COMMIT) prevents any further matches being tried, so the overall
result is "no match".
There are also other start-up optimizations. For example, a minimum
length for the subject may be recorded. Consider the pattern
(*MARK:A)(X|Y)
The minimum length for a match is one character. If the subject is
"ABC", there will be attempts to match "ABC", "BC", and "C". An attempt
to match an empty string at the end of the subject does not take place,
because PCRE2 knows that the subject is now too short, and so the
(*MARK) is never encountered. In this case, the optimization does not
affect the overall match result, which is still "no match", but it does
affect the auxiliary information that is returned.
PCRE2_NO_UTF_CHECK
When PCRE2_UTF is set, the validity of the pattern as a UTF string is
automatically checked. There are discussions about the validity of
UTF-8 strings, UTF-16 strings, and UTF-32 strings in the pcre2unicode
document. If an invalid UTF sequence is found, pcre2_compile() returns
a negative error code.
If you know that your pattern is a valid UTF string, and you want to
skip this check for performance reasons, you can set the
PCRE2_NO_UTF_CHECK option. When it is set, the effect of passing an
invalid UTF string as a pattern is undefined. It may cause your program
to crash or loop.
Note that this option can also be passed to pcre2_match() and
pcre_dfa_match(), to suppress UTF validity checking of the subject
string.
Note also that setting PCRE2_NO_UTF_CHECK at compile time does not dis‐
able the error that is given if an escape sequence for an invalid Uni‐
code code point is encountered in the pattern. In particular, the so-
called "surrogate" code points (0xd800 to 0xdfff) are invalid. If you
want to allow escape sequences such as \x{d800} you can set the
PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES extra option, as described in the
section entitled "Extra compile options" below. However, this is pos‐
sible only in UTF-8 and UTF-32 modes, because these values are not rep‐
resentable in UTF-16.
PCRE2_UCP
This option changes the way PCRE2 processes \B, \b, \D, \d, \S, \s, \W,
\w, and some of the POSIX character classes. By default, only ASCII
characters are recognized, but if PCRE2_UCP is set, Unicode properties
are used instead to classify characters. More details are given in the
section on generic character types in the pcre2pattern page. If you set
PCRE2_UCP, matching one of the items it affects takes much longer. The
option is available only if PCRE2 has been compiled with Unicode sup‐
port (which is the default).
PCRE2_UNGREEDY
This option inverts the "greediness" of the quantifiers so that they
are not greedy by default, but become greedy if followed by "?". It is
not compatible with Perl. It can also be set by a (?U) option setting
within the pattern.
PCRE2_USE_OFFSET_LIMIT
This option must be set for pcre2_compile() if pcre2_set_offset_limit()
is going to be used to set a non-default offset limit in a match con‐
text for matches that use this pattern. An error is generated if an
offset limit is set without this option. For more details, see the
description of pcre2_set_offset_limit() in the section that describes
match contexts. See also the PCRE2_FIRSTLINE option above.
PCRE2_UTF
This option causes PCRE2 to regard both the pattern and the subject
strings that are subsequently processed as strings of UTF characters
instead of single-code-unit strings. It is available when PCRE2 is
built to include Unicode support (which is the default). If Unicode
support is not available, the use of this option provokes an error.
Details of how PCRE2_UTF changes the behaviour of PCRE2 are given in
the pcre2unicode page. In particular, note that it changes the way
PCRE2_CASELESS handles characters with code points greater than 127.
Extra compile options
Unlike the main compile-time options, the extra options are not saved
with the compiled pattern. The option bits that can be set in a compile
context by calling the pcre2_set_compile_extra_options() function are
as follows:
PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES
This option applies when compiling a pattern in UTF-8 or UTF-32 mode.
It is forbidden in UTF-16 mode, and ignored in non-UTF modes. Unicode
"surrogate" code points in the range 0xd800 to 0xdfff are used in pairs
in UTF-16 to encode code points with values in the range 0x10000 to
0x10ffff. The surrogates cannot therefore be represented in UTF-16.
They can be represented in UTF-8 and UTF-32, but are defined as invalid
code points, and cause errors if encountered in a UTF-8 or UTF-32
string that is being checked for validity by PCRE2.
These values also cause errors if encountered in escape sequences such
as \x{d912} within a pattern. However, it seems that some applications,
when using PCRE2 to check for unwanted characters in UTF-8 strings,
explicitly test for the surrogates using escape sequences. The
PCRE2_NO_UTF_CHECK option does not disable the error that occurs,
because it applies only to the testing of input strings for UTF valid‐
ity.
If the extra option PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES is set, surro‐
gate code point values in UTF-8 and UTF-32 patterns no longer provoke
errors and are incorporated in the compiled pattern. However, they can
only match subject characters if the matching function is called with
PCRE2_NO_UTF_CHECK set.
PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL
This is a dangerous option. Use with care. By default, an unrecognized
escape such as \j or a malformed one such as \x{2z} causes a compile-
time error when detected by pcre2_compile(). Perl is somewhat inconsis‐
tent in handling such items: for example, \j is treated as a literal
"j", and non-hexadecimal digits in \x{} are just ignored, though warn‐
ings are given in both cases if Perl's warning switch is enabled. How‐
ever, a malformed octal number after \o{ always causes an error in
Perl.
If the PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL extra option is passed to
pcre2_compile(), all unrecognized or erroneous escape sequences are
treated as single-character escapes. For example, \j is a literal "j"
and \x{2z} is treated as the literal string "x{2z}". Setting this
option means that typos in patterns may go undetected and have unex‐
pected results. This is a dangerous option. Use with care.
PCRE2_EXTRA_MATCH_LINE
This option is provided for use by the -x option of pcre2grep. It
causes the pattern only to match complete lines. This is achieved by
automatically inserting the code for "^(?:" at the start of the com‐
piled pattern and ")$" at the end. Thus, when PCRE2_MULTILINE is set,
the matched line may be in the middle of the subject string. This
option can be used with PCRE2_LITERAL.
PCRE2_EXTRA_MATCH_WORD
This option is provided for use by the -w option of pcre2grep. It
causes the pattern only to match strings that have a word boundary at
the start and the end. This is achieved by automatically inserting the
code for "\b(?:" at the start of the compiled pattern and ")\b" at the
end. The option may be used with PCRE2_LITERAL. However, it is ignored
if PCRE2_EXTRA_MATCH_LINE is also set.
JUST-IN-TIME (JIT) COMPILATION
int pcre2_jit_compile(pcre2_code *code, uint32_t options);
int pcre2_jit_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);
void pcre2_jit_free_unused_memory(pcre2_general_context *gcontext);
pcre2_jit_stack *pcre2_jit_stack_create(PCRE2_SIZE startsize,
PCRE2_SIZE maxsize, pcre2_general_context *gcontext);
void pcre2_jit_stack_assign(pcre2_match_context *mcontext,
pcre2_jit_callback callback_function, void *callback_data);
void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);
These functions provide support for JIT compilation, which, if the
just-in-time compiler is available, further processes a compiled pat‐
tern into machine code that executes much faster than the pcre2_match()
interpretive matching function. Full details are given in the pcre2jit
documentation.
JIT compilation is a heavyweight optimization. It can take some time
for patterns to be analyzed, and for one-off matches and simple pat‐
terns the benefit of faster execution might be offset by a much slower
compilation time. Most (but not all) patterns can be optimized by the
JIT compiler.
LOCALE SUPPORT
PCRE2 handles caseless matching, and determines whether characters are
letters, digits, or whatever, by reference to a set of tables, indexed
by character code point. This applies only to characters whose code
points are less than 256. By default, higher-valued code points never
match escapes such as \w or \d. However, if PCRE2 is built with Uni‐
code support, all characters can be tested with \p and \P, or, alterna‐
tively, the PCRE2_UCP option can be set when a pattern is compiled;
this causes \w and friends to use Unicode property support instead of
the built-in tables.
The use of locales with Unicode is discouraged. If you are handling
characters with code points greater than 128, you should either use
Unicode support, or use locales, but not try to mix the two.
PCRE2 contains an internal set of character tables that are used by
default. These are sufficient for many applications. Normally, the
internal tables recognize only ASCII characters. However, when PCRE2 is
built, it is possible to cause the internal tables to be rebuilt in the
default "C" locale of the local system, which may cause them to be dif‐
ferent.
The internal tables can be overridden by tables supplied by the appli‐
cation that calls PCRE2. These may be created in a different locale
from the default. As more and more applications change to using Uni‐
code, the need for this locale support is expected to die away.
External tables are built by calling the pcre2_maketables() function,
in the relevant locale. The result can be passed to pcre2_compile() as
often as necessary, by creating a compile context and calling
pcre2_set_character_tables() to set the tables pointer therein. For
example, to build and use tables that are appropriate for the French
locale (where accented characters with values greater than 128 are
treated as letters), the following code could be used:
setlocale(LC_CTYPE, "fr_FR");
tables = pcre2_maketables(NULL);
ccontext = pcre2_compile_context_create(NULL);
pcre2_set_character_tables(ccontext, tables);
re = pcre2_compile(..., ccontext);
The locale name "fr_FR" is used on Linux and other Unix-like systems;
if you are using Windows, the name for the French locale is "french".
It is the caller's responsibility to ensure that the memory containing
the tables remains available for as long as it is needed.
The pointer that is passed (via the compile context) to pcre2_compile()
is saved with the compiled pattern, and the same tables are used by
pcre2_match() and pcre_dfa_match(). Thus, for any single pattern, com‐
pilation and matching both happen in the same locale, but different
patterns can be processed in different locales.
INFORMATION ABOUT A COMPILED PATTERN
int pcre2_pattern_info(const pcre2 *code, uint32_t what, void *where);
The pcre2_pattern_info() function returns general information about a
compiled pattern. For information about callouts, see the next section.
The first argument for pcre2_pattern_info() is a pointer to the com‐
piled pattern. The second argument specifies which piece of information
is required, and the third argument is a pointer to a variable to
receive the data. If the third argument is NULL, the first argument is
ignored, and the function returns the size in bytes of the variable
that is required for the information requested. Otherwise, the yield of
the function is zero for success, or one of the following negative num‐
bers:
PCRE2_ERROR_NULL the argument code was NULL
PCRE2_ERROR_BADMAGIC the "magic number" was not found
PCRE2_ERROR_BADOPTION the value of what was invalid
PCRE2_ERROR_UNSET the requested field is not set
The "magic number" is placed at the start of each compiled pattern as
an simple check against passing an arbitrary memory pointer. Here is a
typical call of pcre2_pattern_info(), to obtain the length of the com‐
piled pattern:
int rc;
size_t length;
rc = pcre2_pattern_info(
re, /* result of pcre2_compile() */
PCRE2_INFO_SIZE, /* what is required */
&length); /* where to put the data */
The possible values for the second argument are defined in pcre2.h, and
are as follows:
PCRE2_INFO_ALLOPTIONS
PCRE2_INFO_ARGOPTIONS
PCRE2_INFO_EXTRAOPTIONS
Return copies of the pattern's options. The third argument should point
to a uint32_t variable. PCRE2_INFO_ARGOPTIONS returns exactly the
options that were passed to pcre2_compile(), whereas PCRE2_INFO_ALLOP‐
TIONS returns the compile options as modified by any top-level (*XXX)
option settings such as (*UTF) at the start of the pattern itself.
PCRE2_INFO_EXTRAOPTIONS returns the extra options that were set in the
compile context by calling the pcre2_set_compile_extra_options() func‐
tion.
For example, if the pattern /(*UTF)abc/ is compiled with the
PCRE2_EXTENDED option, the result for PCRE2_INFO_ALLOPTIONS is
PCRE2_EXTENDED and PCRE2_UTF. Option settings such as (?i) that can
change within a pattern do not affect the result of PCRE2_INFO_ALLOP‐
TIONS, even if they appear right at the start of the pattern. (This was
different in some earlier releases.)
A pattern compiled without PCRE2_ANCHORED is automatically anchored by
PCRE2 if the first significant item in every top-level branch is one of
the following:
^ unless PCRE2_MULTILINE is set
\A always
\G always
.* sometimes - see below
When .* is the first significant item, anchoring is possible only when
all the following are true:
.* is not in an atomic group
.* is not in a capturing group that is the subject
of a backreference
PCRE2_DOTALL is in force for .*
Neither (*PRUNE) nor (*SKIP) appears in the pattern
PCRE2_NO_DOTSTAR_ANCHOR is not set
For patterns that are auto-anchored, the PCRE2_ANCHORED bit is set in
the options returned for PCRE2_INFO_ALLOPTIONS.
PCRE2_INFO_BACKREFMAX
Return the number of the highest backreference in the pattern. The
third argument should point to an uint32_t variable. Named subpatterns
acquire numbers as well as names, and these count towards the highest
backreference. Backreferences such as \4 or \g{12} match the captured
characters of the given group, but in addition, the check that a cap‐
turing group is set in a conditional subpattern such as (?(3)a|b) is
also a backreference. Zero is returned if there are no backreferences.
PCRE2_INFO_BSR
The output is a uint32_t integer whose value indicates what character
sequences the \R escape sequence matches. A value of PCRE2_BSR_UNICODE
means that \R matches any Unicode line ending sequence; a value of
PCRE2_BSR_ANYCRLF means that \R matches only CR, LF, or CRLF.
PCRE2_INFO_CAPTURECOUNT
Return the highest capturing subpattern number in the pattern. In pat‐
terns where (?| is not used, this is also the total number of capturing
subpatterns. The third argument should point to an uint32_t variable.
PCRE2_INFO_DEPTHLIMIT
If the pattern set a backtracking depth limit by including an item of
the form (*LIMIT_DEPTH=nnnn) at the start, the value is returned. The
third argument should point to a uint32_t integer. If no such value has
been set, the call to pcre2_pattern_info() returns the error
PCRE2_ERROR_UNSET. Note that this limit will only be used during match‐
ing if it is less than the limit set or defaulted by the caller of the
match function.
PCRE2_INFO_FIRSTBITMAP
In the absence of a single first code unit for a non-anchored pattern,
pcre2_compile() may construct a 256-bit table that defines a fixed set
of values for the first code unit in any match. For example, a pattern
that starts with [abc] results in a table with three bits set. When
code unit values greater than 255 are supported, the flag bit for 255
means "any code unit of value 255 or above". If such a table was con‐
structed, a pointer to it is returned. Otherwise NULL is returned. The
third argument should point to a const uint8_t * variable.
PCRE2_INFO_FIRSTCODETYPE
Return information about the first code unit of any matched string, for
a non-anchored pattern. The third argument should point to an uint32_t
variable. If there is a fixed first value, for example, the letter "c"
from a pattern such as (cat|cow|coyote), 1 is returned, and the value
can be retrieved using PCRE2_INFO_FIRSTCODEUNIT. If there is no fixed
first value, but it is known that a match can occur only at the start
of the subject or following a newline in the subject, 2 is returned.
Otherwise, and for anchored patterns, 0 is returned.
PCRE2_INFO_FIRSTCODEUNIT
Return the value of the first code unit of any matched string for a
pattern where PCRE2_INFO_FIRSTCODETYPE returns 1; otherwise return 0.
The third argument should point to an uint32_t variable. In the 8-bit
library, the value is always less than 256. In the 16-bit library the
value can be up to 0xffff. In the 32-bit library in UTF-32 mode the
value can be up to 0x10ffff, and up to 0xffffffff when not using UTF-32
mode.
PCRE2_INFO_FRAMESIZE
Return the size (in bytes) of the data frames that are used to remember
backtracking positions when the pattern is processed by pcre2_match()
without the use of JIT. The third argument should point to a size_t
variable. The frame size depends on the number of capturing parentheses
in the pattern. Each additional capturing group adds two PCRE2_SIZE
variables.
PCRE2_INFO_HASBACKSLASHC
Return 1 if the pattern contains any instances of \C, otherwise 0. The
third argument should point to an uint32_t variable.
PCRE2_INFO_HASCRORLF
Return 1 if the pattern contains any explicit matches for CR or LF
characters, otherwise 0. The third argument should point to an uint32_t
variable. An explicit match is either a literal CR or LF character, or
\r or \n or one of the equivalent hexadecimal or octal escape
sequences.
PCRE2_INFO_HEAPLIMIT
If the pattern set a heap memory limit by including an item of the form
(*LIMIT_HEAP=nnnn) at the start, the value is returned. The third argu‐
ment should point to a uint32_t integer. If no such value has been set,
the call to pcre2_pattern_info() returns the error PCRE2_ERROR_UNSET.
Note that this limit will only be used during matching if it is less
than the limit set or defaulted by the caller of the match function.
PCRE2_INFO_JCHANGED
Return 1 if the (?J) or (?-J) option setting is used in the pattern,
otherwise 0. The third argument should point to an uint32_t variable.
(?J) and (?-J) set and unset the local PCRE2_DUPNAMES option, respec‐
tively.
PCRE2_INFO_JITSIZE
If the compiled pattern was successfully processed by pcre2_jit_com‐
pile(), return the size of the JIT compiled code, otherwise return
zero. The third argument should point to a size_t variable.
PCRE2_INFO_LASTCODETYPE
Returns 1 if there is a rightmost literal code unit that must exist in
any matched string, other than at its start. The third argument should
point to an uint32_t variable. If there is no such value, 0 is
returned. When 1 is returned, the code unit value itself can be
retrieved using PCRE2_INFO_LASTCODEUNIT. For anchored patterns, a last
literal value is recorded only if it follows something of variable
length. For example, for the pattern /^a\d+z\d+/ the returned value is
1 (with "z" returned from PCRE2_INFO_LASTCODEUNIT), but for /^a\dz\d/
the returned value is 0.
PCRE2_INFO_LASTCODEUNIT
Return the value of the rightmost literal code unit that must exist in
any matched string, other than at its start, for a pattern where
PCRE2_INFO_LASTCODETYPE returns 1. Otherwise, return 0. The third argu‐
ment should point to an uint32_t variable.
PCRE2_INFO_MATCHEMPTY
Return 1 if the pattern might match an empty string, otherwise 0. The
third argument should point to an uint32_t variable. When a pattern
contains recursive subroutine calls it is not always possible to deter‐
mine whether or not it can match an empty string. PCRE2 takes a cau‐
tious approach and returns 1 in such cases.
PCRE2_INFO_MATCHLIMIT
If the pattern set a match limit by including an item of the form
(*LIMIT_MATCH=nnnn) at the start, the value is returned. The third
argument should point to a uint32_t integer. If no such value has been
set, the call to pcre2_pattern_info() returns the error
PCRE2_ERROR_UNSET. Note that this limit will only be used during match‐
ing if it is less than the limit set or defaulted by the caller of the
match function.
PCRE2_INFO_MAXLOOKBEHIND
Return the number of characters (not code units) in the longest lookbe‐
hind assertion in the pattern. The third argument should point to a
uint32_t integer. This information is useful when doing multi-segment
matching using the partial matching facilities. Note that the simple
assertions \b and \B require a one-character lookbehind. \A also regis‐
ters a one-character lookbehind, though it does not actually inspect
the previous character. This is to ensure that at least one character
from the old segment is retained when a new segment is processed. Oth‐
erwise, if there are no lookbehinds in the pattern, \A might match
incorrectly at the start of a second or subsequent segment.
PCRE2_INFO_MINLENGTH
If a minimum length for matching subject strings was computed, its
value is returned. Otherwise the returned value is 0. The value is a
number of characters, which in UTF mode may be different from the num‐
ber of code units. The third argument should point to an uint32_t
variable. The value is a lower bound to the length of any matching
string. There may not be any strings of that length that do actually
match, but every string that does match is at least that long.
PCRE2_INFO_NAMECOUNT
PCRE2_INFO_NAMEENTRYSIZE
PCRE2_INFO_NAMETABLE
PCRE2 supports the use of named as well as numbered capturing parenthe‐
ses. The names are just an additional way of identifying the parenthe‐
ses, which still acquire numbers. Several convenience functions such as
pcre2_substring_get_byname() are provided for extracting captured sub‐
strings by name. It is also possible to extract the data directly, by
first converting the name to a number in order to access the correct
pointers in the output vector (described with pcre2_match() below). To
do the conversion, you need to use the name-to-number map, which is
described by these three values.
The map consists of a number of fixed-size entries. PCRE2_INFO_NAME‐
COUNT gives the number of entries, and PCRE2_INFO_NAMEENTRYSIZE gives
the size of each entry in code units; both of these return a uint32_t
value. The entry size depends on the length of the longest name.
PCRE2_INFO_NAMETABLE returns a pointer to the first entry of the table.
This is a PCRE2_SPTR pointer to a block of code units. In the 8-bit
library, the first two bytes of each entry are the number of the cap‐
turing parenthesis, most significant byte first. In the 16-bit library,
the pointer points to 16-bit code units, the first of which contains
the parenthesis number. In the 32-bit library, the pointer points to
32-bit code units, the first of which contains the parenthesis number.
The rest of the entry is the corresponding name, zero terminated.
The names are in alphabetical order. If (?| is used to create multiple
groups with the same number, as described in the section on duplicate
subpattern numbers in the pcre2pattern page, the groups may be given
the same name, but there is only one entry in the table. Different
names for groups of the same number are not permitted.
Duplicate names for subpatterns with different numbers are permitted,
but only if PCRE2_DUPNAMES is set. They appear in the table in the
order in which they were found in the pattern. In the absence of (?|
this is the order of increasing number; when (?| is used this is not
necessarily the case because later subpatterns may have lower numbers.
As a simple example of the name/number table, consider the following
pattern after compilation by the 8-bit library (assume PCRE2_EXTENDED
is set, so white space - including newlines - is ignored):
(?<date> (?<year>(\d\d)?\d\d) -
(?<month>\d\d) - (?<day>\d\d) )
There are four named subpatterns, so the table has four entries, and
each entry in the table is eight bytes long. The table is as follows,
with non-printing bytes shows in hexadecimal, and undefined bytes shown
as ??:
00 01 d a t e 00 ??
00 05 d a y 00 ?? ??
00 04 m o n t h 00
00 02 y e a r 00 ??
When writing code to extract data from named subpatterns using the
name-to-number map, remember that the length of the entries is likely
to be different for each compiled pattern.
PCRE2_INFO_NEWLINE
The output is one of the following uint32_t values:
PCRE2_NEWLINE_CR Carriage return (CR)
PCRE2_NEWLINE_LF Linefeed (LF)
PCRE2_NEWLINE_CRLF Carriage return, linefeed (CRLF)
PCRE2_NEWLINE_ANY Any Unicode line ending
PCRE2_NEWLINE_ANYCRLF Any of CR, LF, or CRLF
PCRE2_NEWLINE_NUL The NUL character (binary zero)
This identifies the character sequence that will be recognized as mean‐
ing "newline" while matching.
PCRE2_INFO_SIZE
Return the size of the compiled pattern in bytes (for all three
libraries). The third argument should point to a size_t variable. This
value includes the size of the general data block that precedes the
code units of the compiled pattern itself. The value that is used when
pcre2_compile() is getting memory in which to place the compiled pat‐
tern may be slightly larger than the value returned by this option,
because there are cases where the code that calculates the size has to
over-estimate. Processing a pattern with the JIT compiler does not
alter the value returned by this option.
INFORMATION ABOUT A PATTERN'S CALLOUTS
int pcre2_callout_enumerate(const pcre2_code *code,
int (*callback)(pcre2_callout_enumerate_block *, void *),
void *user_data);
A script language that supports the use of string arguments in callouts
might like to scan all the callouts in a pattern before running the
match. This can be done by calling pcre2_callout_enumerate(). The first
argument is a pointer to a compiled pattern, the second points to a
callback function, and the third is arbitrary user data. The callback
function is called for every callout in the pattern in the order in
which they appear. Its first argument is a pointer to a callout enumer‐
ation block, and its second argument is the user_data value that was
passed to pcre2_callout_enumerate(). The contents of the callout enu‐
meration block are described in the pcre2callout documentation, which
also gives further details about callouts.
SERIALIZATION AND PRECOMPILING
It is possible to save compiled patterns on disc or elsewhere, and
reload them later, subject to a number of restrictions. The host on
which the patterns are reloaded must be running the same version of
PCRE2, with the same code unit width, and must also have the same endi‐
anness, pointer width, and PCRE2_SIZE type. Before compiled patterns
can be saved, they must be converted to a "serialized" form, which in
the case of PCRE2 is really just a bytecode dump. The functions whose
names begin with pcre2_serialize_ are used for converting to and from
the serialized form. They are described in the pcre2serialize documen‐
tation. Note that PCRE2 serialization does not convert compiled pat‐
terns to an abstract format like Java or .NET serialization.
THE MATCH DATA BLOCK
pcre2_match_data *pcre2_match_data_create(uint32_t ovecsize,
pcre2_general_context *gcontext);
pcre2_match_data *pcre2_match_data_create_from_pattern(
const pcre2_code *code, pcre2_general_context *gcontext);
void pcre2_match_data_free(pcre2_match_data *match_data);
Information about a successful or unsuccessful match is placed in a
match data block, which is an opaque structure that is accessed by
function calls. In particular, the match data block contains a vector
of offsets into the subject string that define the matched part of the
subject and any substrings that were captured. This is known as the
ovector.
Before calling pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match()
you must create a match data block by calling one of the creation func‐
tions above. For pcre2_match_data_create(), the first argument is the
number of pairs of offsets in the ovector. One pair of offsets is
required to identify the string that matched the whole pattern, with an
additional pair for each captured substring. For example, a value of 4
creates enough space to record the matched portion of the subject plus
three captured substrings. A minimum of at least 1 pair is imposed by
pcre2_match_data_create(), so it is always possible to return the over‐
all matched string.
The second argument of pcre2_match_data_create() is a pointer to a gen‐
eral context, which can specify custom memory management for obtaining
the memory for the match data block. If you are not using custom memory
management, pass NULL, which causes malloc() to be used.
For pcre2_match_data_create_from_pattern(), the first argument is a
pointer to a compiled pattern. The ovector is created to be exactly the
right size to hold all the substrings a pattern might capture. The sec‐
ond argument is again a pointer to a general context, but in this case
if NULL is passed, the memory is obtained using the same allocator that
was used for the compiled pattern (custom or default).
A match data block can be used many times, with the same or different
compiled patterns. You can extract information from a match data block
after a match operation has finished, using functions that are
described in the sections on matched strings and other match data
below.
When a call of pcre2_match() fails, valid data is available in the
match block only when the error is PCRE2_ERROR_NOMATCH,
PCRE2_ERROR_PARTIAL, or one of the error codes for an invalid UTF
string. Exactly what is available depends on the error, and is detailed
below.
When one of the matching functions is called, pointers to the compiled
pattern and the subject string are set in the match data block so that
they can be referenced by the extraction functions. After running a
match, you must not free a compiled pattern or a subject string until
after all operations on the match data block (for that match) have
taken place.
When a match data block itself is no longer needed, it should be freed
by calling pcre2_match_data_free(). If this function is called with a
NULL argument, it returns immediately, without doing anything.
MATCHING A PATTERN: THE TRADITIONAL FUNCTION
int pcre2_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);
The function pcre2_match() is called to match a subject string against
a compiled pattern, which is passed in the code argument. You can call
pcre2_match() with the same code argument as many times as you like, in
order to find multiple matches in the subject string or to match dif‐
ferent subject strings with the same pattern.
This function is the main matching facility of the library, and it
operates in a Perl-like manner. For specialist use there is also an
alternative matching function, which is described below in the section
about the pcre2_dfa_match() function.
Here is an example of a simple call to pcre2_match():
pcre2_match_data *md = pcre2_match_data_create(4, NULL);
int rc = pcre2_match(
re, /* result of pcre2_compile() */
"some string", /* the subject string */
11, /* the length of the subject string */
0, /* start at offset 0 in the subject */
0, /* default options */
md, /* the match data block */
NULL); /* a match context; NULL means use defaults */
If the subject string is zero-terminated, the length can be given as
PCRE2_ZERO_TERMINATED. A match context must be provided if certain less
common matching parameters are to be changed. For details, see the sec‐
tion on the match context above.
The string to be matched by pcre2_match()
The subject string is passed to pcre2_match() as a pointer in subject,
a length in length, and a starting offset in startoffset. The length
and offset are in code units, not characters. That is, they are in
bytes for the 8-bit library, 16-bit code units for the 16-bit library,
and 32-bit code units for the 32-bit library, whether or not UTF pro‐
cessing is enabled.
If startoffset is greater than the length of the subject, pcre2_match()
returns PCRE2_ERROR_BADOFFSET. When the starting offset is zero, the
search for a match starts at the beginning of the subject, and this is
by far the most common case. In UTF-8 or UTF-16 mode, the starting off‐
set must point to the start of a character, or to the end of the sub‐
ject (in UTF-32 mode, one code unit equals one character, so all off‐
sets are valid). Like the pattern string, the subject may contain
binary zeros.
A non-zero starting offset is useful when searching for another match
in the same subject by calling pcre2_match() again after a previous
success. Setting startoffset differs from passing over a shortened
string and setting PCRE2_NOTBOL in the case of a pattern that begins
with any kind of lookbehind. For example, consider the pattern
\Biss\B
which finds occurrences of "iss" in the middle of words. (\B matches
only if the current position in the subject is not a word boundary.)
When applied to the string "Mississipi" the first call to pcre2_match()
finds the first occurrence. If pcre2_match() is called again with just
the remainder of the subject, namely "issipi", it does not match,
because \B is always false at the start of the subject, which is deemed
to be a word boundary. However, if pcre2_match() is passed the entire
string again, but with startoffset set to 4, it finds the second occur‐
rence of "iss" because it is able to look behind the starting point to
discover that it is preceded by a letter.
Finding all the matches in a subject is tricky when the pattern can
match an empty string. It is possible to emulate Perl's /g behaviour by
first trying the match again at the same offset, with the
PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED options, and then if that
fails, advancing the starting offset and trying an ordinary match
again. There is some code that demonstrates how to do this in the
pcre2demo sample program. In the most general case, you have to check
to see if the newline convention recognizes CRLF as a newline, and if
so, and the current character is CR followed by LF, advance the start‐
ing offset by two characters instead of one.
If a non-zero starting offset is passed when the pattern is anchored, a
single attempt to match at the given offset is made. This can only suc‐
ceed if the pattern does not require the match to be at the start of
the subject. In other words, the anchoring must be the result of set‐
ting the PCRE2_ANCHORED option or the use of .* with PCRE2_DOTALL, not
by starting the pattern with ^ or \A.
Option bits for pcre2_match()
The unused bits of the options argument for pcre2_match() must be zero.
The only bits that may be set are PCRE2_ANCHORED, PCRE2_ENDANCHORED,
PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY, PCRE2_NOTEMPTY_ATSTART,
PCRE2_NO_JIT, PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, and PCRE2_PAR‐
TIAL_SOFT. Their action is described below.
Setting PCRE2_ANCHORED or PCRE2_ENDANCHORED at match time is not sup‐
ported by the just-in-time (JIT) compiler. If it is set, JIT matching
is disabled and the interpretive code in pcre2_match() is run. Apart
from PCRE2_NO_JIT (obviously), the remaining options are supported for
JIT matching.
PCRE2_ANCHORED
The PCRE2_ANCHORED option limits pcre2_match() to matching at the first
matching position. If a pattern was compiled with PCRE2_ANCHORED, or
turned out to be anchored by virtue of its contents, it cannot be made
unachored at matching time. Note that setting the option at match time
disables JIT matching.
PCRE2_ENDANCHORED
If the PCRE2_ENDANCHORED option is set, any string that pcre2_match()
matches must be right at the end of the subject string. Note that set‐
ting the option at match time disables JIT matching.
PCRE2_NOTBOL
This option specifies that first character of the subject string is not
the beginning of a line, so the circumflex metacharacter should not
match before it. Setting this without having set PCRE2_MULTILINE at
compile time causes circumflex never to match. This option affects only
the behaviour of the circumflex metacharacter. It does not affect \A.
PCRE2_NOTEOL
This option specifies that the end of the subject string is not the end
of a line, so the dollar metacharacter should not match it nor (except
in multiline mode) a newline immediately before it. Setting this with‐
out having set PCRE2_MULTILINE at compile time causes dollar never to
match. This option affects only the behaviour of the dollar metacharac‐
ter. It does not affect \Z or \z.
PCRE2_NOTEMPTY
An empty string is not considered to be a valid match if this option is
set. If there are alternatives in the pattern, they are tried. If all
the alternatives match the empty string, the entire match fails. For
example, if the pattern
a?b?
is applied to a string not beginning with "a" or "b", it matches an
empty string at the start of the subject. With PCRE2_NOTEMPTY set, this
match is not valid, so pcre2_match() searches further into the string
for occurrences of "a" or "b".
PCRE2_NOTEMPTY_ATSTART
This is like PCRE2_NOTEMPTY, except that it locks out an empty string
match only at the first matching position, that is, at the start of the
subject plus the starting offset. An empty string match later in the
subject is permitted. If the pattern is anchored, such a match can
occur only if the pattern contains \K.
PCRE2_NO_JIT
By default, if a pattern has been successfully processed by
pcre2_jit_compile(), JIT is automatically used when pcre2_match() is
called with options that JIT supports. Setting PCRE2_NO_JIT disables
the use of JIT; it forces matching to be done by the interpreter.
PCRE2_NO_UTF_CHECK
When PCRE2_UTF is set at compile time, the validity of the subject as a
UTF string is checked by default when pcre2_match() is subsequently
called. If a non-zero starting offset is given, the check is applied
only to that part of the subject that could be inspected during match‐
ing, and there is a check that the starting offset points to the first
code unit of a character or to the end of the subject. If there are no
lookbehind assertions in the pattern, the check starts at the starting
offset. Otherwise, it starts at the length of the longest lookbehind
before the starting offset, or at the start of the subject if there are
not that many characters before the starting offset. Note that the
sequences \b and \B are one-character lookbehinds.
The check is carried out before any other processing takes place, and a
negative error code is returned if the check fails. There are several
UTF error codes for each code unit width, corresponding to different
problems with the code unit sequence. There are discussions about the
validity of UTF-8 strings, UTF-16 strings, and UTF-32 strings in the
pcre2unicode page.
If you know that your subject is valid, and you want to skip these
checks for performance reasons, you can set the PCRE2_NO_UTF_CHECK
option when calling pcre2_match(). You might want to do this for the
second and subsequent calls to pcre2_match() if you are making repeated
calls to find other matches in the same subject string.
Warning: When PCRE2_NO_UTF_CHECK is set, the effect of passing an
invalid string as a subject, or an invalid value of startoffset, is
undefined. Your program may crash or loop indefinitely.
PCRE2_PARTIAL_HARD
PCRE2_PARTIAL_SOFT
These options turn on the partial matching feature. A partial match
occurs if the end of the subject string is reached successfully, but
there are not enough subject characters to complete the match. If this
happens when PCRE2_PARTIAL_SOFT (but not PCRE2_PARTIAL_HARD) is set,
matching continues by testing any remaining alternatives. Only if no
complete match can be found is PCRE2_ERROR_PARTIAL returned instead of
PCRE2_ERROR_NOMATCH. In other words, PCRE2_PARTIAL_SOFT specifies that
the caller is prepared to handle a partial match, but only if no com‐
plete match can be found.
If PCRE2_PARTIAL_HARD is set, it overrides PCRE2_PARTIAL_SOFT. In this
case, if a partial match is found, pcre2_match() immediately returns
PCRE2_ERROR_PARTIAL, without considering any other alternatives. In
other words, when PCRE2_PARTIAL_HARD is set, a partial match is consid‐
ered to be more important that an alternative complete match.
There is a more detailed discussion of partial and multi-segment match‐
ing, with examples, in the pcre2partial documentation.
NEWLINE HANDLING WHEN MATCHING
When PCRE2 is built, a default newline convention is set; this is usu‐
ally the standard convention for the operating system. The default can
be overridden in a compile context by calling pcre2_set_newline(). It
can also be overridden by starting a pattern string with, for example,
(*CRLF), as described in the section on newline conventions in the
pcre2pattern page. During matching, the newline choice affects the be‐
haviour of the dot, circumflex, and dollar metacharacters. It may also
alter the way the match starting position is advanced after a match
failure for an unanchored pattern.
When PCRE2_NEWLINE_CRLF, PCRE2_NEWLINE_ANYCRLF, or PCRE2_NEWLINE_ANY is
set as the newline convention, and a match attempt for an unanchored
pattern fails when the current starting position is at a CRLF sequence,
and the pattern contains no explicit matches for CR or LF characters,
the match position is advanced by two characters instead of one, in
other words, to after the CRLF.
The above rule is a compromise that makes the most common cases work as
expected. For example, if the pattern is .+A (and the PCRE2_DOTALL
option is not set), it does not match the string "\r\nA" because, after
failing at the start, it skips both the CR and the LF before retrying.
However, the pattern [\r\n]A does match that string, because it con‐
tains an explicit CR or LF reference, and so advances only by one char‐
acter after the first failure.
An explicit match for CR of LF is either a literal appearance of one of
those characters in the pattern, or one of the \r or \n or equivalent
octal or hexadecimal escape sequences. Implicit matches such as [^X] do
not count, nor does \s, even though it includes CR and LF in the char‐
acters that it matches.
Notwithstanding the above, anomalous effects may still occur when CRLF
is a valid newline sequence and explicit \r or \n escapes appear in the
pattern.
HOW PCRE2_MATCH() RETURNS A STRING AND CAPTURED SUBSTRINGS
uint32_t pcre2_get_ovector_count(pcre2_match_data *match_data);
PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);
In general, a pattern matches a certain portion of the subject, and in
addition, further substrings from the subject may be picked out by
parenthesized parts of the pattern. Following the usage in Jeffrey
Friedl's book, this is called "capturing" in what follows, and the
phrase "capturing subpattern" or "capturing group" is used for a frag‐
ment of a pattern that picks out a substring. PCRE2 supports several
other kinds of parenthesized subpattern that do not cause substrings to
be captured. The pcre2_pattern_info() function can be used to find out
how many capturing subpatterns there are in a compiled pattern.
You can use auxiliary functions for accessing captured substrings by
number or by name, as described in sections below.
Alternatively, you can make direct use of the vector of PCRE2_SIZE val‐
ues, called the ovector, which contains the offsets of captured
strings. It is part of the match data block. The function
pcre2_get_ovector_pointer() returns the address of the ovector, and
pcre2_get_ovector_count() returns the number of pairs of values it con‐
tains.
Within the ovector, the first in each pair of values is set to the off‐
set of the first code unit of a substring, and the second is set to the
offset of the first code unit after the end of a substring. These val‐
ues are always code unit offsets, not character offsets. That is, they
are byte offsets in the 8-bit library, 16-bit offsets in the 16-bit
library, and 32-bit offsets in the 32-bit library.
After a partial match (error return PCRE2_ERROR_PARTIAL), only the
first pair of offsets (that is, ovector[0] and ovector[1]) are set.
They identify the part of the subject that was partially matched. See
the pcre2partial documentation for details of partial matching.
After a fully successful match, the first pair of offsets identifies
the portion of the subject string that was matched by the entire pat‐
tern. The next pair is used for the first captured substring, and so
on. The value returned by pcre2_match() is one more than the highest
numbered pair that has been set. For example, if two substrings have
been captured, the returned value is 3. If there are no captured sub‐
strings, the return value from a successful match is 1, indicating that
just the first pair of offsets has been set.
If a pattern uses the \K escape sequence within a positive assertion,
the reported start of a successful match can be greater than the end of
the match. For example, if the pattern (?=ab\K) is matched against
"ab", the start and end offset values for the match are 2 and 0.
If a capturing subpattern group is matched repeatedly within a single
match operation, it is the last portion of the subject that it matched
that is returned.
If the ovector is too small to hold all the captured substring offsets,
as much as possible is filled in, and the function returns a value of
zero. If captured substrings are not of interest, pcre2_match() may be
called with a match data block whose ovector is of minimum length (that
is, one pair).
It is possible for capturing subpattern number n+1 to match some part
of the subject when subpattern n has not been used at all. For example,
if the string "abc" is matched against the pattern (a|(z))(bc) the
return from the function is 4, and subpatterns 1 and 3 are matched, but
2 is not. When this happens, both values in the offset pairs corre‐
sponding to unused subpatterns are set to PCRE2_UNSET.
Offset values that correspond to unused subpatterns at the end of the
expression are also set to PCRE2_UNSET. For example, if the string
"abc" is matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3
are not matched. The return from the function is 2, because the high‐
est used capturing subpattern number is 1. The offsets for for the sec‐
ond and third capturing subpatterns (assuming the vector is large
enough, of course) are set to PCRE2_UNSET.
Elements in the ovector that do not correspond to capturing parentheses
in the pattern are never changed. That is, if a pattern contains n cap‐
turing parentheses, no more than ovector[0] to ovector[2n+1] are set by
pcre2_match(). The other elements retain whatever values they previ‐
ously had. After a failed match attempt, the contents of the ovector
are unchanged.
OTHER INFORMATION ABOUT A MATCH
PCRE2_SPTR pcre2_get_mark(pcre2_match_data *match_data);
PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);
As well as the offsets in the ovector, other information about a match
is retained in the match data block and can be retrieved by the above
functions in appropriate circumstances. If they are called at other
times, the result is undefined.
After a successful match, a partial match (PCRE2_ERROR_PARTIAL), or a
failure to match (PCRE2_ERROR_NOMATCH), a (*MARK), (*PRUNE), or (*THEN)
name may be available. The function pcre2_get_mark() can be called to
access this name. The same function applies to all three verbs. It
returns a pointer to the zero-terminated name, which is within the com‐
piled pattern. If no name is available, NULL is returned. The length of
the name (excluding the terminating zero) is stored in the code unit
that precedes the name. You should use this length instead of relying
on the terminating zero if the name might contain a binary zero.
After a successful match, the name that is returned is the last
(*MARK), (*PRUNE), or (*THEN) name encountered on the matching path
through the pattern. Instances of (*PRUNE) and (*THEN) without names
are ignored. Thus, for example, if the matching path contains
(*MARK:A)(*PRUNE), the name "A" is returned. After a "no match" or a
partial match, the last encountered name is returned. For example,
consider this pattern:
^(*MARK:A)((*MARK:B)a|b)c
When it matches "bc", the returned name is A. The B mark is "seen" in
the first branch of the group, but it is not on the matching path. On
the other hand, when this pattern fails to match "bx", the returned
name is B.
Warning: By default, certain start-of-match optimizations are used to
give a fast "no match" result in some situations. For example, if the
anchoring is removed from the pattern above, there is an initial check
for the presence of "c" in the subject before running the matching
engine. This check fails for "bx", causing a match failure without see‐
ing any marks. You can disable the start-of-match optimizations by set‐
ting the PCRE2_NO_START_OPTIMIZE option for pcre2_compile() or starting
the pattern with (*NO_START_OPT).
After a successful match, a partial match, or one of the invalid UTF
errors (for example, PCRE2_ERROR_UTF8_ERR5), pcre2_get_startchar() can
be called. After a successful or partial match it returns the code unit
offset of the character at which the match started. For a non-partial
match, this can be different to the value of ovector[0] if the pattern
contains the \K escape sequence. After a partial match, however, this
value is always the same as ovector[0] because \K does not affect the
result of a partial match.
After a UTF check failure, pcre2_get_startchar() can be used to obtain
the code unit offset of the invalid UTF character. Details are given in
the pcre2unicode page.
ERROR RETURNS FROM pcre2_match()
If pcre2_match() fails, it returns a negative number. This can be con‐
verted to a text string by calling the pcre2_get_error_message() func‐
tion (see "Obtaining a textual error message" below). Negative error
codes are also returned by other functions, and are documented with
them. The codes are given names in the header file. If UTF checking is
in force and an invalid UTF subject string is detected, one of a number
of UTF-specific negative error codes is returned. Details are given in
the pcre2unicode page. The following are the other errors that may be
returned by pcre2_match():
PCRE2_ERROR_NOMATCH
The subject string did not match the pattern.
PCRE2_ERROR_PARTIAL
The subject string did not match, but it did match partially. See the
pcre2partial documentation for details of partial matching.
PCRE2_ERROR_BADMAGIC
PCRE2 stores a 4-byte "magic number" at the start of the compiled code,
to catch the case when it is passed a junk pointer. This is the error
that is returned when the magic number is not present.
PCRE2_ERROR_BADMODE
This error is given when a compiled pattern is passed to a function in
a library of a different code unit width, for example, a pattern com‐
piled by the 8-bit library is passed to a 16-bit or 32-bit library
function.
PCRE2_ERROR_BADOFFSET
The value of startoffset was greater than the length of the subject.
PCRE2_ERROR_BADOPTION
An unrecognized bit was set in the options argument.
PCRE2_ERROR_BADUTFOFFSET
The UTF code unit sequence that was passed as a subject was checked and
found to be valid (the PCRE2_NO_UTF_CHECK option was not set), but the
value of startoffset did not point to the beginning of a UTF character
or the end of the subject.
PCRE2_ERROR_CALLOUT
This error is never generated by pcre2_match() itself. It is provided
for use by callout functions that want to cause pcre2_match() or
pcre2_callout_enumerate() to return a distinctive error code. See the
pcre2callout documentation for details.
PCRE2_ERROR_DEPTHLIMIT
The nested backtracking depth limit was reached.
PCRE2_ERROR_HEAPLIMIT
The heap limit was reached.
PCRE2_ERROR_INTERNAL
An unexpected internal error has occurred. This error could be caused
by a bug in PCRE2 or by overwriting of the compiled pattern.
PCRE2_ERROR_JIT_STACKLIMIT
This error is returned when a pattern that was successfully studied
using JIT is being matched, but the memory available for the just-in-
time processing stack is not large enough. See the pcre2jit documenta‐
tion for more details.
PCRE2_ERROR_MATCHLIMIT
The backtracking match limit was reached.
PCRE2_ERROR_NOMEMORY
If a pattern contains many nested backtracking points, heap memory is
used to remember them. This error is given when the memory allocation
function (default or custom) fails. Note that a different error,
PCRE2_ERROR_HEAPLIMIT, is given if the amount of memory needed exceeds
the heap limit.
PCRE2_ERROR_NULL
Either the code, subject, or match_data argument was passed as NULL.
PCRE2_ERROR_RECURSELOOP
This error is returned when pcre2_match() detects a recursion loop
within the pattern. Specifically, it means that either the whole pat‐
tern or a subpattern has been called recursively for the second time at
the same position in the subject string. Some simple patterns that
might do this are detected and faulted at compile time, but more com‐
plicated cases, in particular mutual recursions between two different
subpatterns, cannot be detected until matching is attempted.
OBTAINING A TEXTUAL ERROR MESSAGE
int pcre2_get_error_message(int errorcode, PCRE2_UCHAR *buffer,
PCRE2_SIZE bufflen);
A text message for an error code from any PCRE2 function (compile,
match, or auxiliary) can be obtained by calling pcre2_get_error_mes‐
sage(). The code is passed as the first argument, with the remaining
two arguments specifying a code unit buffer and its length in code
units, into which the text message is placed. The message is returned
in code units of the appropriate width for the library that is being
used.
The returned message is terminated with a trailing zero, and the func‐
tion returns the number of code units used, excluding the trailing
zero. If the error number is unknown, the negative error code
PCRE2_ERROR_BADDATA is returned. If the buffer is too small, the mes‐
sage is truncated (but still with a trailing zero), and the negative
error code PCRE2_ERROR_NOMEMORY is returned. None of the messages are
very long; a buffer size of 120 code units is ample.
EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
int pcre2_substring_length_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_SIZE *length);
int pcre2_substring_copy_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR *buffer,
PCRE2_SIZE *bufflen);
int pcre2_substring_get_bynumber(pcre2_match_data *match_data,
uint32_t number, PCRE2_UCHAR **bufferptr,
PCRE2_SIZE *bufflen);
void pcre2_substring_free(PCRE2_UCHAR *buffer);
Captured substrings can be accessed directly by using the ovector as
described above. For convenience, auxiliary functions are provided for
extracting captured substrings as new, separate, zero-terminated
strings. A substring that contains a binary zero is correctly extracted
and has a further zero added on the end, but the result is not, of
course, a C string.
The functions in this section identify substrings by number. The number
zero refers to the entire matched substring, with higher numbers refer‐
ring to substrings captured by parenthesized groups. After a partial
match, only substring zero is available. An attempt to extract any
other substring gives the error PCRE2_ERROR_PARTIAL. The next section
describes similar functions for extracting captured substrings by name.
If a pattern uses the \K escape sequence within a positive assertion,
the reported start of a successful match can be greater than the end of
the match. For example, if the pattern (?=ab\K) is matched against
"ab", the start and end offset values for the match are 2 and 0. In
this situation, calling these functions with a zero substring number
extracts a zero-length empty string.
You can find the length in code units of a captured substring without
extracting it by calling pcre2_substring_length_bynumber(). The first
argument is a pointer to the match data block, the second is the group
number, and the third is a pointer to a variable into which the length
is placed. If you just want to know whether or not the substring has
been captured, you can pass the third argument as NULL.
The pcre2_substring_copy_bynumber() function copies a captured sub‐
string into a supplied buffer, whereas pcre2_substring_get_bynumber()
copies it into new memory, obtained using the same memory allocation
function that was used for the match data block. The first two argu‐
ments of these functions are a pointer to the match data block and a
capturing group number.
The final arguments of pcre2_substring_copy_bynumber() are a pointer to
the buffer and a pointer to a variable that contains its length in code
units. This is updated to contain the actual number of code units used
for the extracted substring, excluding the terminating zero.
For pcre2_substring_get_bynumber() the third and fourth arguments point
to variables that are updated with a pointer to the new memory and the
number of code units that comprise the substring, again excluding the
terminating zero. When the substring is no longer needed, the memory
should be freed by calling pcre2_substring_free().
The return value from all these functions is zero for success, or a
negative error code. If the pattern match failed, the match failure
code is returned. If a substring number greater than zero is used
after a partial match, PCRE2_ERROR_PARTIAL is returned. Other possible
error codes are:
PCRE2_ERROR_NOMEMORY
The buffer was too small for pcre2_substring_copy_bynumber(), or the
attempt to get memory failed for pcre2_substring_get_bynumber().
PCRE2_ERROR_NOSUBSTRING
There is no substring with that number in the pattern, that is, the
number is greater than the number of capturing parentheses.
PCRE2_ERROR_UNAVAILABLE
The substring number, though not greater than the number of captures in
the pattern, is greater than the number of slots in the ovector, so the
substring could not be captured.
PCRE2_ERROR_UNSET
The substring did not participate in the match. For example, if the
pattern is (abc)|(def) and the subject is "def", and the ovector con‐
tains at least two capturing slots, substring number 1 is unset.
EXTRACTING A LIST OF ALL CAPTURED SUBSTRINGS
int pcre2_substring_list_get(pcre2_match_data *match_data,
PCRE2_UCHAR ***listptr, PCRE2_SIZE **lengthsptr);
void pcre2_substring_list_free(PCRE2_SPTR *list);
The pcre2_substring_list_get() function extracts all available sub‐
strings and builds a list of pointers to them. It also (optionally)
builds a second list that contains their lengths (in code units),
excluding a terminating zero that is added to each of them. All this is
done in a single block of memory that is obtained using the same memory
allocation function that was used to get the match data block.
This function must be called only after a successful match. If called
after a partial match, the error code PCRE2_ERROR_PARTIAL is returned.
The address of the memory block is returned via listptr, which is also
the start of the list of string pointers. The end of the list is marked
by a NULL pointer. The address of the list of lengths is returned via
lengthsptr. If your strings do not contain binary zeros and you do not
therefore need the lengths, you may supply NULL as the lengthsptr argu‐
ment to disable the creation of a list of lengths. The yield of the
function is zero if all went well, or PCRE2_ERROR_NOMEMORY if the mem‐
ory block could not be obtained. When the list is no longer needed, it
should be freed by calling pcre2_substring_list_free().
If this function encounters a substring that is unset, which can happen
when capturing subpattern number n+1 matches some part of the subject,
but subpattern n has not been used at all, it returns an empty string.
This can be distinguished from a genuine zero-length substring by
inspecting the appropriate offset in the ovector, which contain
PCRE2_UNSET for unset substrings, or by calling pcre2_sub‐
string_length_bynumber().
EXTRACTING CAPTURED SUBSTRINGS BY NAME
int pcre2_substring_number_from_name(const pcre2_code *code,
PCRE2_SPTR name);
int pcre2_substring_length_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_SIZE *length);
int pcre2_substring_copy_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen);
int pcre2_substring_get_byname(pcre2_match_data *match_data,
PCRE2_SPTR name, PCRE2_UCHAR **bufferptr, PCRE2_SIZE *bufflen);
void pcre2_substring_free(PCRE2_UCHAR *buffer);
To extract a substring by name, you first have to find associated num‐
ber. For example, for this pattern:
(a+)b(?<xxx>\d+)...
the number of the subpattern called "xxx" is 2. If the name is known to
be unique (PCRE2_DUPNAMES was not set), you can find the number from
the name by calling pcre2_substring_number_from_name(). The first argu‐
ment is the compiled pattern, and the second is the name. The yield of
the function is the subpattern number, PCRE2_ERROR_NOSUBSTRING if there
is no subpattern of that name, or PCRE2_ERROR_NOUNIQUESUBSTRING if
there is more than one subpattern of that name. Given the number, you
can extract the substring directly from the ovector, or use one of the
"bynumber" functions described above.
For convenience, there are also "byname" functions that correspond to
the "bynumber" functions, the only difference being that the second
argument is a name instead of a number. If PCRE2_DUPNAMES is set and
there are duplicate names, these functions scan all the groups with the
given name, and return the first named string that is set.
If there are no groups with the given name, PCRE2_ERROR_NOSUBSTRING is
returned. If all groups with the name have numbers that are greater
than the number of slots in the ovector, PCRE2_ERROR_UNAVAILABLE is
returned. If there is at least one group with a slot in the ovector,
but no group is found to be set, PCRE2_ERROR_UNSET is returned.
Warning: If the pattern uses the (?| feature to set up multiple subpat‐
terns with the same number, as described in the section on duplicate
subpattern numbers in the pcre2pattern page, you cannot use names to
distinguish the different subpatterns, because names are not included
in the compiled code. The matching process uses only numbers. For this
reason, the use of different names for subpatterns of the same number
causes an error at compile time.
CREATING A NEW STRING WITH SUBSTITUTIONS
int pcre2_substitute(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext, PCRE2_SPTR replacement,
PCRE2_SIZE rlength, PCRE2_UCHAR *outputbufferfP,
PCRE2_SIZE *outlengthptr);
This function calls pcre2_match() and then makes a copy of the subject
string in outputbuffer, replacing the part that was matched with the
replacement string, whose length is supplied in rlength. This can be
given as PCRE2_ZERO_TERMINATED for a zero-terminated string. Matches in
which a \K item in a lookahead in the pattern causes the match to end
before it starts are not supported, and give rise to an error return.
For global replacements, matches in which \K in a lookbehind causes the
match to start earlier than the point that was reached in the previous
iteration are also not supported.
The first seven arguments of pcre2_substitute() are the same as for
pcre2_match(), except that the partial matching options are not permit‐
ted, and match_data may be passed as NULL, in which case a match data
block is obtained and freed within this function, using memory manage‐
ment functions from the match context, if provided, or else those that
were used to allocate memory for the compiled code.
If an external match_data block is provided, its contents afterwards
are those set by the final call to pcre2_match(), which will have ended
in a matching error. The contents of the ovector within the match data
block may or may not have been changed.
The outlengthptr argument must point to a variable that contains the
length, in code units, of the output buffer. If the function is suc‐
cessful, the value is updated to contain the length of the new string,
excluding the trailing zero that is automatically added.
If the function is not successful, the value set via outlengthptr
depends on the type of error. For syntax errors in the replacement
string, the value is the offset in the replacement string where the
error was detected. For other errors, the value is PCRE2_UNSET by
default. This includes the case of the output buffer being too small,
unless PCRE2_SUBSTITUTE_OVERFLOW_LENGTH is set (see below), in which
case the value is the minimum length needed, including space for the
trailing zero. Note that in order to compute the required length,
pcre2_substitute() has to simulate all the matching and copying,
instead of giving an error return as soon as the buffer overflows. Note
also that the length is in code units, not bytes.
In the replacement string, which is interpreted as a UTF string in UTF
mode, and is checked for UTF validity unless the PCRE2_NO_UTF_CHECK
option is set, a dollar character is an escape character that can spec‐
ify the insertion of characters from capturing groups or (*MARK),
(*PRUNE), or (*THEN) items in the pattern. The following forms are
always recognized:
$$ insert a dollar character
$<n> or ${<n>} insert the contents of group <n>
$*MARK or ${*MARK} insert a (*MARK), (*PRUNE), or (*THEN) name
Either a group number or a group name can be given for <n>. Curly
brackets are required only if the following character would be inter‐
preted as part of the number or name. The number may be zero to include
the entire matched string. For example, if the pattern a(b)c is
matched with "=abc=" and the replacement string "+$1$0$1+", the result
is "=+babcb+=".
$*MARK inserts the name from the last encountered (*MARK), (*PRUNE), or
(*THEN) on the matching path that has a name. (*MARK) must always
include a name, but (*PRUNE) and (*THEN) need not. For example, in the
case of (*MARK:A)(*PRUNE) the name inserted is "A", but for
(*MARK:A)(*PRUNE:B) the relevant name is "B". This facility can be
used to perform simple simultaneous substitutions, as this pcre2test
example shows:
/(*MARK:pear)apple|(*MARK:orange)lemon/g,replace=${*MARK}
apple lemon
2: pear orange
As well as the usual options for pcre2_match(), a number of additional
options can be set in the options argument of pcre2_substitute().
PCRE2_SUBSTITUTE_GLOBAL causes the function to iterate over the subject
string, replacing every matching substring. If this option is not set,
only the first matching substring is replaced. The search for matches
takes place in the original subject string (that is, previous replace‐
ments do not affect it). Iteration is implemented by advancing the
startoffset value for each search, which is always passed the entire
subject string. If an offset limit is set in the match context, search‐
ing stops when that limit is reached.
You can restrict the effect of a global substitution to a portion of
the subject string by setting either or both of startoffset and an off‐
set limit. Here is a pcre2test example:
/B/g,replace=!,use_offset_limit
ABC ABC ABC ABC\=offset=3,offset_limit=12
2: ABC A!C A!C ABC
When continuing with global substitutions after matching a substring
with zero length, an attempt to find a non-empty match at the same off‐
set is performed. If this is not successful, the offset is advanced by
one character except when CRLF is a valid newline sequence and the next
two characters are CR, LF. In this case, the offset is advanced by two
characters.
PCRE2_SUBSTITUTE_OVERFLOW_LENGTH changes what happens when the output
buffer is too small. The default action is to return PCRE2_ERROR_NOMEM‐
ORY immediately. If this option is set, however, pcre2_substitute()
continues to go through the motions of matching and substituting (with‐
out, of course, writing anything) in order to compute the size of buf‐
fer that is needed. This value is passed back via the outlengthptr
variable, with the result of the function still being
PCRE2_ERROR_NOMEMORY.
Passing a buffer size of zero is a permitted way of finding out how
much memory is needed for given substitution. However, this does mean
that the entire operation is carried out twice. Depending on the appli‐
cation, it may be more efficient to allocate a large buffer and free
the excess afterwards, instead of using PCRE2_SUBSTITUTE_OVER‐
FLOW_LENGTH.
PCRE2_SUBSTITUTE_UNKNOWN_UNSET causes references to capturing groups
that do not appear in the pattern to be treated as unset groups. This
option should be used with care, because it means that a typo in a
group name or number no longer causes the PCRE2_ERROR_NOSUBSTRING
error.
PCRE2_SUBSTITUTE_UNSET_EMPTY causes unset capturing groups (including
unknown groups when PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set) to be
treated as empty strings when inserted as described above. If this
option is not set, an attempt to insert an unset group causes the
PCRE2_ERROR_UNSET error. This option does not influence the extended
substitution syntax described below.
PCRE2_SUBSTITUTE_EXTENDED causes extra processing to be applied to the
replacement string. Without this option, only the dollar character is
special, and only the group insertion forms listed above are valid.
When PCRE2_SUBSTITUTE_EXTENDED is set, two things change:
Firstly, backslash in a replacement string is interpreted as an escape
character. The usual forms such as \n or \x{ddd} can be used to specify
particular character codes, and backslash followed by any non-alphanu‐
meric character quotes that character. Extended quoting can be coded
using \Q...\E, exactly as in pattern strings.
There are also four escape sequences for forcing the case of inserted
letters. The insertion mechanism has three states: no case forcing,
force upper case, and force lower case. The escape sequences change the
current state: \U and \L change to upper or lower case forcing, respec‐
tively, and \E (when not terminating a \Q quoted sequence) reverts to
no case forcing. The sequences \u and \l force the next character (if
it is a letter) to upper or lower case, respectively, and then the
state automatically reverts to no case forcing. Case forcing applies to
all inserted characters, including those from captured groups and let‐
ters within \Q...\E quoted sequences.
Note that case forcing sequences such as \U...\E do not nest. For exam‐
ple, the result of processing "\Uaa\LBB\Ecc\E" is "AAbbcc"; the final
\E has no effect.
The second effect of setting PCRE2_SUBSTITUTE_EXTENDED is to add more
flexibility to group substitution. The syntax is similar to that used
by Bash:
${<n>:-<string>}
${<n>:+<string1>:<string2>}
As before, <n> may be a group number or a name. The first form speci‐
fies a default value. If group <n> is set, its value is inserted; if
not, <string> is expanded and the result inserted. The second form
specifies strings that are expanded and inserted when group <n> is set
or unset, respectively. The first form is just a convenient shorthand
for
${<n>:+${<n>}:<string>}
Backslash can be used to escape colons and closing curly brackets in
the replacement strings. A change of the case forcing state within a
replacement string remains in force afterwards, as shown in this
pcre2test example:
/(some)?(body)/substitute_extended,replace=${1:+\U:\L}HeLLo
body
1: hello
somebody
1: HELLO
The PCRE2_SUBSTITUTE_UNSET_EMPTY option does not affect these extended
substitutions. However, PCRE2_SUBSTITUTE_UNKNOWN_UNSET does cause
unknown groups in the extended syntax forms to be treated as unset.
If successful, pcre2_substitute() returns the number of replacements
that were made. This may be zero if no matches were found, and is never
greater than 1 unless PCRE2_SUBSTITUTE_GLOBAL is set.
In the event of an error, a negative error code is returned. Except for
PCRE2_ERROR_NOMATCH (which is never returned), errors from
pcre2_match() are passed straight back.
PCRE2_ERROR_NOSUBSTRING is returned for a non-existent substring inser‐
tion, unless PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set.
PCRE2_ERROR_UNSET is returned for an unset substring insertion (includ‐
ing an unknown substring when PCRE2_SUBSTITUTE_UNKNOWN_UNSET is set)
when the simple (non-extended) syntax is used and PCRE2_SUBSTI‐
TUTE_UNSET_EMPTY is not set.
PCRE2_ERROR_NOMEMORY is returned if the output buffer is not big
enough. If the PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option is set, the size
of buffer that is needed is returned via outlengthptr. Note that this
does not happen by default.
PCRE2_ERROR_BADREPLACEMENT is used for miscellaneous syntax errors in
the replacement string, with more particular errors being
PCRE2_ERROR_BADREPESCAPE (invalid escape sequence), PCRE2_ERROR_REP‐
MISSINGBRACE (closing curly bracket not found), PCRE2_ERROR_BADSUBSTI‐
TUTION (syntax error in extended group substitution), and
PCRE2_ERROR_BADSUBSPATTERN (the pattern match ended before it started
or the match started earlier than the current position in the subject,
which can happen if \K is used in an assertion).
As for all PCRE2 errors, a text message that describes the error can be
obtained by calling the pcre2_get_error_message() function (see
"Obtaining a textual error message" above).
DUPLICATE SUBPATTERN NAMES
int pcre2_substring_nametable_scan(const pcre2_code *code,
PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last);
When a pattern is compiled with the PCRE2_DUPNAMES option, names for
subpatterns are not required to be unique. Duplicate names are always
allowed for subpatterns with the same number, created by using the (?|
feature. Indeed, if such subpatterns are named, they are required to
use the same names.
Normally, patterns with duplicate names are such that in any one match,
only one of the named subpatterns participates. An example is shown in
the pcre2pattern documentation.
When duplicates are present, pcre2_substring_copy_byname() and
pcre2_substring_get_byname() return the first substring corresponding
to the given name that is set. Only if none are set is
PCRE2_ERROR_UNSET is returned. The pcre2_substring_number_from_name()
function returns the error PCRE2_ERROR_NOUNIQUESUBSTRING when there are
duplicate names.
If you want to get full details of all captured substrings for a given
name, you must use the pcre2_substring_nametable_scan() function. The
first argument is the compiled pattern, and the second is the name. If
the third and fourth arguments are NULL, the function returns a group
number for a unique name, or PCRE2_ERROR_NOUNIQUESUBSTRING otherwise.
When the third and fourth arguments are not NULL, they must be pointers
to variables that are updated by the function. After it has run, they
point to the first and last entries in the name-to-number table for the
given name, and the function returns the length of each entry in code
units. In both cases, PCRE2_ERROR_NOSUBSTRING is returned if there are
no entries for the given name.
The format of the name table is described above in the section entitled
Information about a pattern. Given all the relevant entries for the
name, you can extract each of their numbers, and hence the captured
data.
FINDING ALL POSSIBLE MATCHES AT ONE POSITION
The traditional matching function uses a similar algorithm to Perl,
which stops when it finds the first match at a given point in the sub‐
ject. If you want to find all possible matches, or the longest possible
match at a given position, consider using the alternative matching
function (see below) instead. If you cannot use the alternative func‐
tion, you can kludge it up by making use of the callout facility, which
is described in the pcre2callout documentation.
What you have to do is to insert a callout right at the end of the pat‐
tern. When your callout function is called, extract and save the cur‐
rent matched substring. Then return 1, which forces pcre2_match() to
backtrack and try other alternatives. Ultimately, when it runs out of
matches, pcre2_match() will yield PCRE2_ERROR_NOMATCH.
MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
int pcre2_dfa_match(const pcre2_code *code, PCRE2_SPTR subject,
PCRE2_SIZE length, PCRE2_SIZE startoffset,
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext,
int *workspace, PCRE2_SIZE wscount);
The function pcre2_dfa_match() is called to match a subject string
against a compiled pattern, using a matching algorithm that scans the
subject string just once (not counting lookaround assertions), and does
not backtrack. This has different characteristics to the normal algo‐
rithm, and is not compatible with Perl. Some of the features of PCRE2
patterns are not supported. Nevertheless, there are times when this
kind of matching can be useful. For a discussion of the two matching
algorithms, and a list of features that pcre2_dfa_match() does not sup‐
port, see the pcre2matching documentation.
The arguments for the pcre2_dfa_match() function are the same as for
pcre2_match(), plus two extras. The ovector within the match data block
is used in a different way, and this is described below. The other com‐
mon arguments are used in the same way as for pcre2_match(), so their
description is not repeated here.
The two additional arguments provide workspace for the function. The
workspace vector should contain at least 20 elements. It is used for
keeping track of multiple paths through the pattern tree. More
workspace is needed for patterns and subjects where there are a lot of
potential matches.
Here is an example of a simple call to pcre2_dfa_match():
int wspace[20];
pcre2_match_data *md = pcre2_match_data_create(4, NULL);
int rc = pcre2_dfa_match(
re, /* result of pcre2_compile() */
"some string", /* the subject string */
11, /* the length of the subject string */
0, /* start at offset 0 in the subject */
0, /* default options */
md, /* the match data block */
NULL, /* a match context; NULL means use defaults */
wspace, /* working space vector */
20); /* number of elements (NOT size in bytes) */
Option bits for pcre_dfa_match()
The unused bits of the options argument for pcre2_dfa_match() must be
zero. The only bits that may be set are PCRE2_ANCHORED, PCRE2_ENDAN‐
CHORED, PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY,
PCRE2_NOTEMPTY_ATSTART, PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD,
PCRE2_PARTIAL_SOFT, PCRE2_DFA_SHORTEST, and PCRE2_DFA_RESTART. All but
the last four of these are exactly the same as for pcre2_match(), so
their description is not repeated here.
PCRE2_PARTIAL_HARD
PCRE2_PARTIAL_SOFT
These have the same general effect as they do for pcre2_match(), but
the details are slightly different. When PCRE2_PARTIAL_HARD is set for
pcre2_dfa_match(), it returns PCRE2_ERROR_PARTIAL if the end of the
subject is reached and there is still at least one matching possibility
that requires additional characters. This happens even if some complete
matches have already been found. When PCRE2_PARTIAL_SOFT is set, the
return code PCRE2_ERROR_NOMATCH is converted into PCRE2_ERROR_PARTIAL
if the end of the subject is reached, there have been no complete
matches, but there is still at least one matching possibility. The por‐
tion of the string that was inspected when the longest partial match
was found is set as the first matching string in both cases. There is a
more detailed discussion of partial and multi-segment matching, with
examples, in the pcre2partial documentation.
PCRE2_DFA_SHORTEST
Setting the PCRE2_DFA_SHORTEST option causes the matching algorithm to
stop as soon as it has found one match. Because of the way the alterna‐
tive algorithm works, this is necessarily the shortest possible match
at the first possible matching point in the subject string.
PCRE2_DFA_RESTART
When pcre2_dfa_match() returns a partial match, it is possible to call
it again, with additional subject characters, and have it continue with
the same match. The PCRE2_DFA_RESTART option requests this action; when
it is set, the workspace and wscount options must reference the same
vector as before because data about the match so far is left in them
after a partial match. There is more discussion of this facility in the
pcre2partial documentation.
Successful returns from pcre2_dfa_match()
When pcre2_dfa_match() succeeds, it may have matched more than one sub‐
string in the subject. Note, however, that all the matches from one run
of the function start at the same point in the subject. The shorter
matches are all initial substrings of the longer matches. For example,
if the pattern
<.*>
is matched against the string
This is <something> <something else> <something further> no more
the three matched strings are
<something> <something else> <something further>
<something> <something else>
<something>
On success, the yield of the function is a number greater than zero,
which is the number of matched substrings. The offsets of the sub‐
strings are returned in the ovector, and can be extracted by number in
the same way as for pcre2_match(), but the numbers bear no relation to
any capturing groups that may exist in the pattern, because DFA match‐
ing does not support group capture.
Calls to the convenience functions that extract substrings by name
return the error PCRE2_ERROR_DFA_UFUNC (unsupported function) if used
after a DFA match. The convenience functions that extract substrings by
number never return PCRE2_ERROR_NOSUBSTRING.
The matched strings are stored in the ovector in reverse order of
length; that is, the longest matching string is first. If there were
too many matches to fit into the ovector, the yield of the function is
zero, and the vector is filled with the longest matches.
NOTE: PCRE2's "auto-possessification" optimization usually applies to
character repeats at the end of a pattern (as well as internally). For
example, the pattern "a\d+" is compiled as if it were "a\d++". For DFA
matching, this means that only one possible match is found. If you
really do want multiple matches in such cases, either use an ungreedy
repeat such as "a\d+?" or set the PCRE2_NO_AUTO_POSSESS option when
compiling.
Error returns from pcre2_dfa_match()
The pcre2_dfa_match() function returns a negative number when it fails.
Many of the errors are the same as for pcre2_match(), as described
above. There are in addition the following errors that are specific to
pcre2_dfa_match():
PCRE2_ERROR_DFA_UITEM
This return is given if pcre2_dfa_match() encounters an item in the
pattern that it does not support, for instance, the use of \C in a UTF
mode or a backreference.
PCRE2_ERROR_DFA_UCOND
This return is given if pcre2_dfa_match() encounters a condition item
that uses a backreference for the condition, or a test for recursion in
a specific group. These are not supported.
PCRE2_ERROR_DFA_WSSIZE
This return is given if pcre2_dfa_match() runs out of space in the
workspace vector.
PCRE2_ERROR_DFA_RECURSE
When a recursive subpattern is processed, the matching function calls
itself recursively, using private memory for the ovector and workspace.
This error is given if the internal ovector is not large enough. This
should be extremely rare, as a vector of size 1000 is used.
PCRE2_ERROR_DFA_BADRESTART
When pcre2_dfa_match() is called with the PCRE2_DFA_RESTART option,
some plausibility checks are made on the contents of the workspace,
which should contain data about the previous partial match. If any of
these checks fail, this error is given.
SEE ALSO
pcre2build(3), pcre2callout(3), pcre2demo(3), pcre2matching(3),
pcre2partial(3), pcre2posix(3), pcre2sample(3), pcre2unicode(3).
AUTHOR
Philip Hazel
University Computing Service
Cambridge, England.
REVISION
Last updated: 07 September 2018
Copyright (c) 1997-2018 University of Cambridge.
PCRE2 10.32 07 September 2018 PCRE2API(3)