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NAME | EXPERIMENTAL PATTERN CONVERSION FUNCTIONS | THE CONVERT CONTEXT | THE CONVERSION FUNCTION | CONVERTING GLOBS | CONVERTING POSIX PATTERNS | AUTHOR | REVISION | COLOPHON |
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PCRE2CONVERT(3) Library Functions Manual PCRE2CONVERT(3)
PCRE2 - Perl-compatible regular expressions (revised API)
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.
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.
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 this
function is called with a NULL argument, it returns immediately
without doing anything.
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().
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_CONVERT_GLOB_NO_STARSTAR matches globs with the double-star
feature disabled. These options may be given together.
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).
Philip Hazel
Retired from University Computing Service
Cambridge, England.
Last updated: 28 June 2018
Copyright (c) 1997-2018 University of Cambridge.
This page is part of the PCRE (Perl Compatible Regular
Expressions) project. Information about the project can be found
at ⟨http://www.pcre.org/⟩. If you have a bug report for this
manual page, see
⟨http://bugs.exim.org/enter_bug.cgi?product=PCRE⟩. This page was
obtained from the tarball fetched from
⟨https://github.com/PhilipHazel/pcre2.git⟩ on 2024-06-14. If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original
manual page), send a mail to [email protected]
PCRE2 10.32 28 June 2018 PCRE2CONVERT(3)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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