Provided by: libpcre2-dev_10.31-2_amd64 
NAME
PCRE2 - Perl-compatible regular expressions (revised API)
EXPERIMENTAL PATTERN CONVERSION FUNCTIONS
This document describes a set of functions that can be used to convert "foreign" patterns into PCRE2
regular expressions. This facility is currently experimental, and may be changed in future releases. Two
kinds of pattern, globs and POSIX patterns, are supported.
THE CONVERT CONTEXT
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);
A convert context is used to hold parameters that affect the way that pattern conversion works. Like all
PCRE2 contexts, you need to use a context only if you want to override the defaults. There are the usual
create, copy, and free functions. If custom memory management functions are set in a general context that
is passed to pcre2_convert_context_create(), they are used for all memory management within the
conversion functions.
There are only two parameters in the convert context at present. Both apply only to glob conversions. The
escape character defaults to grave accent under Windows, otherwise backslash. It can be set to zero,
meaning no escape character, or to any punctuation character with a code point less than 256. The
separator character defaults to backslash under Windows, otherwise forward slash. It can be set to
forward slash, backslash, or dot.
The two setting functions return zero on success, or PCRE2_ERROR_BADDATA if their second argument is
invalid.
THE CONVERSION FUNCTION
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);
The first two arguments of pcre2_pattern_convert() define the foreign pattern that is to be converted.
The length may be given as PCRE2_ZERO_TERMINATED. The options argument defines how the pattern is to be
processed. If the input is UTF, the PCRE2_CONVERT_UTF option should be set. PCRE2_CONVERT_NO_UTF_CHECK
may also be set if you are sure the input is valid. One or more of the glob options, or one of the
following POSIX options must be set to define the type of conversion that is required:
PCRE2_CONVERT_GLOB
PCRE2_CONVERT_GLOB_NO_WILD_SEPARATOR
PCRE2_CONVERT_GLOB_NO_STARSTAR
PCRE2_CONVERT_POSIX_BASIC
PCRE2_CONVERT_POSIX_EXTENDED
Details of the conversions are given below. The buffer and blength arguments define how the output is
handled:
If buffer is NULL, the function just returns the length of the converted pattern via blength. This is one
less than the length of buffer needed, because a terminating zero is always added to the output.
If buffer points to a NULL pointer, an output buffer is obtained using the allocator in the context or
malloc() if no context is supplied. A pointer to this buffer is placed in the variable to which buffer
points. When no longer needed the output buffer must be freed by calling pcre2_converted_pattern_free().
If buffer points to a non-NULL pointer, blength must be set to the actual length of the buffer provided
(in code units).
In all cases, after successful conversion, the variable pointed to by blength is updated to the length
actually used (in code units), excluding the terminating zero that is always added.
If an error occurs, the length (via blength) is set to the offset within the input pattern where the
error was detected. Only gross syntax errors are caught; there are plenty of errors that will get passed
on for pcre2_compile() to discover.
The return from pcre2_pattern_convert() is zero on success or a non-zero PCRE2 error code. Note that
PCRE2 error codes may be positive or negative: pcre2_compile() uses mostly positive codes and
pcre2_match() negative ones; pcre2_convert() uses existing codes of both kinds. A textual error message
can be obtained by calling pcre2_get_error_message().
CONVERTING GLOBS
Globs are used to match file names, and consequently have the concept of a "path separator", which
defaults to backslash under Windows and forward slash otherwise. If PCRE2_CONVERT_GLOB is set, the
wildcards * and ? are not permitted to match separator characters, but the double-star (**) feature
(which does match separators) is supported.
PCRE2_CONVERT_GLOB_NO_WILD_SEPARATOR matches globs with wildcards allowed to match separator characters.
PCRE2_GLOB_NO_STARSTAR matches globs with the double-star feature disabled. These options may be given
together.
CONVERTING POSIX PATTERNS
POSIX defines two kinds of regular expression pattern: basic and extended. These can be processed by
setting PCRE2_CONVERT_POSIX_BASIC or PCRE2_CONVERT_POSIX_EXTENDED, respectively.
In POSIX patterns, backslash is not special in a character class. Unmatched closing parentheses are
treated as literals.
In basic patterns, ? + | {} and () must be escaped to be recognized as metacharacters outside a character
class. If the first character in the pattern is * it is treated as a literal. ^ is a metacharacter only
at the start of a branch.
In extended patterns, a backslash not in a character class always makes the next character literal,
whatever it is. There are no backreferences.
Note: POSIX mandates that the longest possible match at the first matching position must be found. This
is not what pcre2_match() does; it yields the first match that is found. An application can use
pcre2_dfa_match() to find the longest match, but that does not support backreferences (but then neither
do POSIX extended patterns).
AUTHOR
Philip Hazel
University Computing Service
Cambridge, England.
REVISION
Last updated: 12 July 2017
Copyright (c) 1997-2017 University of Cambridge.