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165 lines
6.5 KiB
165 lines
6.5 KiB
.TH PCRE2CONVERT 3 "28 June 2018" "PCRE2 10.32"
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.SH NAME
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PCRE2 - Perl-compatible regular expressions (revised API)
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.SH "EXPERIMENTAL PATTERN CONVERSION FUNCTIONS"
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.rs
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.sp
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This document describes a set of functions that can be used to convert
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"foreign" patterns into PCRE2 regular expressions. This facility is currently
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experimental, and may be changed in future releases. Two kinds of pattern,
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globs and POSIX patterns, are supported.
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.
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.
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.SH "THE CONVERT CONTEXT"
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.rs
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.sp
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.nf
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.B pcre2_convert_context *pcre2_convert_context_create(
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.B " pcre2_general_context *\fIgcontext\fP);"
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.sp
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.B pcre2_convert_context *pcre2_convert_context_copy(
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.B " pcre2_convert_context *\fIcvcontext\fP);"
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.sp
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.B void pcre2_convert_context_free(pcre2_convert_context *\fIcvcontext\fP);
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.sp
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.B int pcre2_set_glob_escape(pcre2_convert_context *\fIcvcontext\fP,
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.B " uint32_t \fIescape_char\fP);"
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.sp
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.B int pcre2_set_glob_separator(pcre2_convert_context *\fIcvcontext\fP,
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.B " uint32_t \fIseparator_char\fP);"
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.fi
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.sp
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A convert context is used to hold parameters that affect the way that pattern
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conversion works. Like all PCRE2 contexts, you need to use a context only if
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you want to override the defaults. There are the usual create, copy, and free
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functions. If custom memory management functions are set in a general context
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that is passed to \fBpcre2_convert_context_create()\fP, they are used for all
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memory management within the conversion functions.
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.P
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There are only two parameters in the convert context at present. Both apply
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only to glob conversions. The escape character defaults to grave accent under
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Windows, otherwise backslash. It can be set to zero, meaning no escape
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character, or to any punctuation character with a code point less than 256.
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The separator character defaults to backslash under Windows, otherwise forward
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slash. It can be set to forward slash, backslash, or dot.
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.P
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The two setting functions return zero on success, or PCRE2_ERROR_BADDATA if
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their second argument is invalid.
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.
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.
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.SH "THE CONVERSION FUNCTION"
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.rs
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.sp
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.nf
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.B int pcre2_pattern_convert(PCRE2_SPTR \fIpattern\fP, PCRE2_SIZE \fIlength\fP,
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.B " uint32_t \fIoptions\fP, PCRE2_UCHAR **\fIbuffer\fP,"
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.B " PCRE2_SIZE *\fIblength\fP, pcre2_convert_context *\fIcvcontext\fP);"
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.sp
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.B void pcre2_converted_pattern_free(PCRE2_UCHAR *\fIconverted_pattern\fP);
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.fi
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.sp
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The first two arguments of \fBpcre2_pattern_convert()\fP define the foreign
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pattern that is to be converted. The length may be given as
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PCRE2_ZERO_TERMINATED. The \fBoptions\fP argument defines how the pattern is to
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be processed. If the input is UTF, the PCRE2_CONVERT_UTF option should be set.
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PCRE2_CONVERT_NO_UTF_CHECK may also be set if you are sure the input is valid.
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One or more of the glob options, or one of the following POSIX options must be
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set to define the type of conversion that is required:
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.sp
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PCRE2_CONVERT_GLOB
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PCRE2_CONVERT_GLOB_NO_WILD_SEPARATOR
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PCRE2_CONVERT_GLOB_NO_STARSTAR
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PCRE2_CONVERT_POSIX_BASIC
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PCRE2_CONVERT_POSIX_EXTENDED
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.sp
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Details of the conversions are given below. The \fBbuffer\fP and \fBblength\fP
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arguments define how the output is handled:
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.P
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If \fBbuffer\fP is NULL, the function just returns the length of the converted
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pattern via \fBblength\fP. This is one less than the length of buffer needed,
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because a terminating zero is always added to the output.
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.P
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If \fBbuffer\fP points to a NULL pointer, an output buffer is obtained using
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the allocator in the context or \fBmalloc()\fP if no context is supplied. A
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pointer to this buffer is placed in the variable to which \fBbuffer\fP points.
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When no longer needed the output buffer must be freed by calling
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\fBpcre2_converted_pattern_free()\fP. If this function is called with a NULL
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argument, it returns immediately without doing anything.
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.P
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If \fBbuffer\fP points to a non-NULL pointer, \fBblength\fP must be set to the
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actual length of the buffer provided (in code units).
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.P
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In all cases, after successful conversion, the variable pointed to by
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\fBblength\fP is updated to the length actually used (in code units), excluding
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the terminating zero that is always added.
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.P
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If an error occurs, the length (via \fBblength\fP) is set to the offset
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within the input pattern where the error was detected. Only gross syntax errors
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are caught; there are plenty of errors that will get passed on for
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\fBpcre2_compile()\fP to discover.
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.P
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The return from \fBpcre2_pattern_convert()\fP is zero on success or a non-zero
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PCRE2 error code. Note that PCRE2 error codes may be positive or negative:
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\fBpcre2_compile()\fP uses mostly positive codes and \fBpcre2_match()\fP
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negative ones; \fBpcre2_convert()\fP uses existing codes of both kinds. A
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textual error message can be obtained by calling
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\fBpcre2_get_error_message()\fP.
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.
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.
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.SH "CONVERTING GLOBS"
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.rs
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.sp
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Globs are used to match file names, and consequently have the concept of a
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"path separator", which defaults to backslash under Windows and forward slash
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otherwise. If PCRE2_CONVERT_GLOB is set, the wildcards * and ? are not
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permitted to match separator characters, but the double-star (**) feature
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(which does match separators) is supported.
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.P
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PCRE2_CONVERT_GLOB_NO_WILD_SEPARATOR matches globs with wildcards allowed to
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match separator characters. PCRE2_GLOB_NO_STARSTAR matches globs with the
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double-star feature disabled. These options may be given together.
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.
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.
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.SH "CONVERTING POSIX PATTERNS"
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.rs
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.sp
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POSIX defines two kinds of regular expression pattern: basic and extended.
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These can be processed by setting PCRE2_CONVERT_POSIX_BASIC or
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PCRE2_CONVERT_POSIX_EXTENDED, respectively.
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.P
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In POSIX patterns, backslash is not special in a character class. Unmatched
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closing parentheses are treated as literals.
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.P
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In basic patterns, ? + | {} and () must be escaped to be recognized
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as metacharacters outside a character class. If the first character in the
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pattern is * it is treated as a literal. ^ is a metacharacter only at the start
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of a branch.
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.P
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In extended patterns, a backslash not in a character class always
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makes the next character literal, whatever it is. There are no backreferences.
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.P
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Note: POSIX mandates that the longest possible match at the first matching
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position must be found. This is not what \fBpcre2_match()\fP does; it yields
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the first match that is found. An application can use \fBpcre2_dfa_match()\fP
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to find the longest match, but that does not support backreferences (but then
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neither do POSIX extended patterns).
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.
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.
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.SH AUTHOR
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.rs
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.sp
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.nf
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Philip Hazel
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University Computing Service
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Cambridge, England.
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.fi
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.
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.
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.SH REVISION
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.rs
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.sp
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.nf
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Last updated: 28 June 2018
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Copyright (c) 1997-2018 University of Cambridge.
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.fi
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