PCRE2

https://www.pcre.org/current/doc/html/
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PCRE2 is a C library providing Perl-compatible regular expression pattern matching with support for...
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### Configure with custom compiler flags and installation prefix

Source: https://www.pcre.org/current/doc/html/README.txt

Example of running the configure script with specific C compiler flags and a custom installation directory.

```bash
CFLAGS='-O2 -Wall' ./configure --prefix=/opt/local
```

--------------------------------

### Quantified (*ACCEPT) example

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

Shows an example of (*ACCEPT) being used with quantification.

```regex
  (A(*ACCEPT)??B)C
```

--------------------------------

### #newline_default example

Source: https://www.pcre.org/current/doc/html/pcre2test.html

Example of the #newline_default command with a list of acceptable newline types.

```plaintext
  #newline_default LF Any anyCRLF

```

--------------------------------

### Callout pattern example

Source: https://www.pcre.org/current/doc/html/pcre2callout.html

Example pattern containing a callout.

```text
  ab(?C4)cd
```

--------------------------------

### Pattern Start Options and Limits

Source: https://www.pcre.org/current/doc/html/pcre2syntax.html

Lists options and limits that are recognized only at the start of a pattern or after specific sequences.

```text
  (*LIMIT_DEPTH=d)     set the backtracking limit to d
  (*LIMIT_HEAP=d)      set the heap size limit to d * 1024 bytes
  (*LIMIT_MATCH=d)     set the match limit to d
  (*CASELESS_RESTRICT) set PCRE2_EXTRA_CASELESS_RESTRICT when matching
  (*NOTEMPTY)          set PCRE2_NOTEMPTY when matching
  (*NOTEMPTY_ATSTART)  set PCRE2_NOTEMPTY_ATSTART when matching
  (*NO_AUTO_POSSESS)   no auto-possessification (PCRE2_NO_AUTO_POSSESS)
  (*NO_DOTSTAR_ANCHOR) no .* anchoring (PCRE2_NO_DOTSTAR_ANCHOR)
  (*NO_JIT)            disable JIT optimization
  (*NO_START_OPT)      no start-match optimization (PCRE2_NO_START_OPTIMIZE)
  (*TURKISH_CASING)    set PCRE2_EXTRA_TURKISH_CASING when matching
  (*UTF)               set appropriate UTF mode for the library in use
  (*UCP)               set PCRE2_UCP (use Unicode properties for \d etc)
```

--------------------------------

### Branch reset group example

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

Example of a branch reset group (?| where alternatives use the same numbers for capturing parentheses.

```regex
  (?|(Sat)ur|(Sun))day
```

--------------------------------

### Retrieve 8-bit library installation path

Source: https://www.pcre.org/current/doc/html/README.txt

Use the pcre2-config command to output information about the 8-bit library installation.

```bash
pcre2-config --libs8
```

--------------------------------

### Quantifier Syntax Examples

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

Examples of various repetition quantifiers applied to literals, character classes, and digits.

```regex
  z{2,4}
```

```regex
  [aeiou]{3,}
```

```regex
  \d{8}
```

```regex
  X{,4} is interpreted as X{0,4}
```

--------------------------------

### Setting a locale example

Source: https://www.pcre.org/current/doc/html/pcre2test.html

Example of using the locale modifier to specify a locale name.

```text
  /pattern/locale=fr_FR
```

--------------------------------

### Internal Option Scope Examples

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

Examples showing how internal option changes affect groups and subsequent pattern parts.

```text
  (a(?i)b)c
```

```text
  (a(?i)b|c)
```

--------------------------------

### Test substring extraction with copy and get modifiers

Source: https://www.pcre.org/current/doc/html/pcre2test.html

Example of using copy and get modifiers to test substring extraction functions with capture groups.

```text
   abcd\=copy=1,copy=3,get=G1
```

--------------------------------

### Get configure help

Source: https://www.pcre.org/current/doc/html/pcre2build.html

Run this command to see the complete list of options available for the configure script.

```bash
  ./configure --help
```

--------------------------------

### Combined BSR configuration

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

An example of combining multiple configuration sequences at the start of a pattern.

```regex
  (*ANY)(*BSR_ANYCRLF)
```

--------------------------------

### Configure static library build

Source: https://www.pcre.org/current/doc/html/README.txt

Example of configuring the build to produce fully statically linked binaries.

```bash
LDFLAGS=--static ./configure --disable-shared
```

--------------------------------

### Example of newline convention in pattern

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

A pattern starting with the (*CR) sequence to define the newline convention.

```text
  (*CR)a.b
```

--------------------------------

### Stack pattern management example

Source: https://www.pcre.org/current/doc/html/pcre2test.html

Demonstrates pushing patterns onto a stack, saving/loading them, and popping them for matching.

```text
  /abc/push
  /xyz/push
  #save tempfile
  #load tempfile
  #pop info
  xyz

  #pop jit,bincode
  abc
```

--------------------------------

### Pattern using \K to reset match start

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

Example of using \K to exclude 'foo' from the final matched sequence.

```regex
  foo\Kbar
```

--------------------------------

### Callouts with string arguments

Source: https://www.pcre.org/current/doc/html/pcre2test.html

Example showing output format when using callouts with string arguments.

```text
    re> /^ab(?C'first')cd(?C"second")ef/
  data> abcdefg
  Callout (7): 'first'
  --->abcdefg
      ^ ^         c
  Callout (20): "second"
  --->abcdefg
      ^   ^       e
   0: abcdef
```

--------------------------------

### Example pattern for DFA matching

Source: https://www.pcre.org/current/doc/html/pcre2matching.html

A sample pattern used to illustrate how the alternative matching algorithm handles multiple potential matches starting at the same point.

```regex
  cat(er(pillar)?)?
```

--------------------------------

### Calling an external program from a pcre2grep callout

Source: https://www.pcre.org/current/doc/html/pcre2grep.html

When the callout string does not start with a pipe, it is parsed as an executable name and arguments separated by pipes. The example shows a call to /bin/echo with arguments and the resulting output.

```shell
executable_name|arg1|arg2|...
```

```shell
echo -e "abcde\n12345" | pcre2grep \
  '(?x)(.)(..(.)
  (?C"/bin/echo|Arg1: [$1] [$2] [$3]|Arg2: $|${1}$| ($4)")()' -

Output:

  Arg1: [a] [bcd] [d] Arg2: |a| ()
  abcde
  Arg1: [1] [234] [4] Arg2: |1| ()
  12345
```

--------------------------------

### Compile pcre2demo.c with standard library paths

Source: https://www.pcre.org/current/doc/html/pcre2sample.html

Compiles the demonstration program using the PCRE2 8-bit library when installed in standard include and library directories.

```bash
  cc -o pcre2demo pcre2demo.c -lpcre2-8

```

--------------------------------

### PCRE2_EXTENDED comment example

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

A pattern that demonstrates the PCRE2_EXTENDED comment syntax. An unescaped # starts a comment that continues to the next newline. The literal newline sequence in the pattern ends the comment; escape sequences that represent a newline do not count.

```regex
  abc #comment \n still comment

```

--------------------------------

### PCRE2 demonstration program source code

Source: https://www.pcre.org/current/doc/html/pcre2demo.html

The full demonstration program source code, including necessary macros and main function setup.

```c
/*************************************************
*           PCRE2 DEMONSTRATION PROGRAM          *
*************************************************/

/* This is a demonstration program to illustrate a straightforward way of
using the PCRE2 regular expression library from a C program. See the
pcre2sample documentation for a short discussion ("man pcre2sample" if you have
the PCRE2 man pages installed). PCRE2 is a revised API for the library, and is
incompatible with the original PCRE API.

There are actually three libraries, each supporting a different code unit
width. This demonstration program uses the 8-bit library. The default is to
process each code unit as a separate character, but if the pattern begins with
"(*UTF)", both it and the subject are treated as UTF-8 strings, where
characters may occupy multiple code units.

In Unix-like environments, if PCRE2 is installed in your standard system
libraries, you should be able to compile this program using this command:

cc -Wall pcre2demo.c -lpcre2-8 -o pcre2demo

If PCRE2 is not installed in a standard place, it is likely to be installed
with support for the pkg-config mechanism. If you have pkg-config, you can
compile this program using this command:

cc -Wall pcre2demo.c `pkg-config --cflags --libs libpcre2-8` -o pcre2demo

If you do not have pkg-config, you may have to use something like this:

cc -Wall pcre2demo.c -I/usr/local/include -L/usr/local/lib \
  -R/usr/local/lib -lpcre2-8 -o pcre2demo

Replace "/usr/local/include" and "/usr/local/lib" with wherever the include and
library files for PCRE2 are installed on your system. Only some operating
systems (Solaris is one) use the -R option.

Building under Windows:

If you want to statically link this program against a non-dll .a file, you must
define PCRE2_STATIC before including pcre2.h, so in this environment, uncomment
the following line. */

/* #define PCRE2_STATIC */

/* The PCRE2_CODE_UNIT_WIDTH macro must be defined before including pcre2.h.
For a program that uses only one code unit width, setting it to 8, 16, or 32
makes it possible to use generic function names such as pcre2_compile(). Note
that just changing 8 to 16 (for example) is not sufficient to convert this
program to process 16-bit characters. Even in a fully 16-bit environment, where
string-handling functions such as strcmp() and printf() work with 16-bit
characters, the code for handling the table of named substrings will still need
to be modified. */

#define PCRE2_CODE_UNIT_WIDTH 8

#include <stdio.h>
#include <string.h>
#include <pcre2.h>


/**************************************************************************
* Here is the program. The API includes the concept of "contexts" for     *
* setting up unusual interface requirements for compiling and matching,   *
* such as custom memory managers and non-standard newline definitions.    *
* This program does not do any of this, so it makes no use of contexts,   *
* always passing NULL where a context could be given.                     *
**************************************************************************/

int main(int argc, char **argv)
{
pcre2_code *re;
PCRE2_SPTR pattern;     /* PCRE2_SPTR is a pointer to unsigned code units of */
PCRE2_SPTR subject;     /* the appropriate width (in this case, 8 bits). */
PCRE2_SPTR name_table;

int errornumber;
int find_all, caseless_match;
int i;
int rc;

uint32_t namecount;
uint32_t name_entry_size;

PCRE2_SIZE erroroffset;
PCRE2_SIZE *ovector;
PCRE2_SIZE ovector_last[2];
PCRE2_SIZE subject_length;

pcre2_match_data *match_data;


/**************************************************************************
* First, sort out the command line. Options:                              *
* - "-g" to request repeated matching to find all occurrences,            *
*   like Perl's /g option. We set the variable find_all to a non-zero     *
*   value if the -g option is present.                                    *
* - "-i" to request caseless matching, like Perl's /i option.  We set the *
*   variable caseless_match to PCRE2_CASELESS if the -i option is         *
*   present.                                                              *
**************************************************************************/

find_all = 0;
caseless_match = 0;
for (i = 1; i < argc; i++)
  {
  if (strcmp(argv[i], "-g") == 0) find_all = 1;
  else if (strcmp(argv[i], "-i") == 0) caseless_match = PCRE2_CASELESS;
  else if (argv[i][0] == '-')
    {
    printf("Unrecognised option %s\n", argv[i]);
    return 1;
    }
  else break;
  }

/* After the options, we require exactly two arguments, which are the pattern,
and the subject string. */
```

--------------------------------

### Equivalent Unicode property specifications

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

Examples showing equivalent ways to specify the same Unicode property, demonstrating loose matching rules.

```regex
  \p{bidiclass=al}
  \p{BC=al}
  \p{ Bidi_Class : AL }
  \p{ Bi-di class = Al }
  \P{ ^ Bi-di class = Al }
```

--------------------------------

### Compile pcre2demo.c with /usr/local paths

Source: https://www.pcre.org/current/doc/html/pcre2sample.html

Compiles the demonstration program when PCRE2 is installed under /usr/local, specifying the include and library directories.

```bash
  cc -o pcre2demo -I/usr/local/include pcre2demo.c -L/usr/local/lib -lpcre2-8

```

--------------------------------

### THEN verb alternation example

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

Example of using the THEN verb within an alternation.

```regex
  ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
```

--------------------------------

### Single-threaded JIT Compilation and Execution

Source: https://www.pcre.org/current/doc/html/pcre2jit.html

This example demonstrates compiling a pattern with JIT, assigning a JIT stack, and executing a match without using a callback.

```c
  int rc;
  pcre2_code *re;
  pcre2_match_data *match_data;
  pcre2_match_context *mcontext;
  pcre2_jit_stack *jit_stack;

  re = pcre2_compile(pattern, PCRE2_ZERO_TERMINATED, 0,
    &errornumber, &erroffset, NULL);
  rc = pcre2_jit_compile(re, PCRE2_JIT_COMPLETE);
  mcontext = pcre2_match_context_create(NULL);
  jit_stack = pcre2_jit_stack_create(32*1024, 512*1024, NULL);
  pcre2_jit_stack_assign(mcontext, NULL, jit_stack);
  match_data = pcre2_match_data_create(re, 10);
  rc = pcre2_match(re, subject, length, 0, 0, match_data, mcontext);
  /* Process result */

  pcre2_code_free(re);
  pcre2_match_data_free(match_data);
  pcre2_match_context_free(mcontext);
  pcre2_jit_stack_free(jit_stack);
```

--------------------------------

### THEN verb nested alternation example

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

Example showing how THEN interacts with nested alternation.

```regex
  A (B(*THEN)C | (*FAIL)) | D
```

--------------------------------

### SKIP verb usage example

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

Example of using the SKIP verb in a pattern.

```regex
  a+(*SKIP)b
```

--------------------------------

### Match context setup actions: callout, limits, memory management

Source: https://www.pcre.org/current/doc/html/pcre2_substitute.html

The actions that can be performed using the match context, including setting a callout function, limiting matching offsets, modifying backtracking limits, and custom memory management.

```plaintext
  Set up a callout function
  Set a matching offset limit
  Change the backtracking match limit
  Change the backtracking depth limit
  Set custom memory management in the match context
```

--------------------------------

### Substitution callout test

Source: https://www.pcre.org/current/doc/html/pcre2test.html

Example of setting up a substitution callout function to inspect input and output strings.

```text
  /abc/g,replace=<$0>,substitute_callout
      abcdefabcpqr
   1(1) Old 0 3 "abc" New 0 5 "<abc>"
   2(1) Old 6 9 "abc" New 8 13 "<abc>"
   2: <abc>def<abc>pqr
```

--------------------------------

### COMMIT verb usage example

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

Example of using the COMMIT verb in a pattern.

```regex
  a+(*COMMIT)b
```

--------------------------------

### Run pcre2demo with sample commands

Source: https://www.pcre.org/current/doc/html/pcre2sample.html

Example invocations of the compiled pcre2demo program, including the -g option for global matching and -i for case-insensitive matching.

```bash
  ./pcre2demo 'cat|dog' 'the cat sat on the mat'
  ./pcre2demo -g 'cat|dog' 'the dog sat on the cat'
  ./pcre2demo -i 'cat' 'the dog sat on the CAT'

```

--------------------------------

### Sequential backtracking verbs example

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

Example of using multiple backtracking verbs in sequence.

```regex
  ...(*COMMIT)(*PRUNE)...
```

--------------------------------

### Multiple backtracking verbs example

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

Example of a pattern containing multiple backtracking verbs.

```regex
  (A(*COMMIT)B(*THEN)C|ABD)
```

--------------------------------

### Example of (*ACCEPT) inside capturing parentheses

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

Demonstrates how (*ACCEPT) captures data when placed inside capturing parentheses.

```regex
  A((?:A|B(*ACCEPT)|C)D)
```

--------------------------------

### Enable JIT compiler support

Source: https://www.pcre.org/current/doc/html/pcre2build.html

Options for enabling Just-in-time (JIT) compiler support during the build process.

```bash
  --enable-jit
```

```bash
  --enable-jit=auto
```

--------------------------------

### THEN verb conditional group example

Source: https://www.pcre.org/current/doc/html/pcre2pattern.html

Example of using the THEN verb within a conditional group.

```regex
  ^.*? (?(?=a) a | b(*THEN)c )
```

--------------------------------

### Anchored pattern example

Source: https://www.pcre.org/current/doc/html/pcre2matching.html

An example of an anchored pattern used to illustrate matching differences.

```text
  ^<.*>
```

--------------------------------

### Displaying numerical callout arguments

Source: https://www.pcre.org/current/doc/html/pcre2test.html

Example of the default output for a numerical callout showing positions and the next pattern item.

```text
  --->pqrabcdef
    0    ^  ^     \d
```
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