diff options
| author | Philip Hazel <ph10@hermes.cam.ac.uk> | 2007-01-23 15:08:45 +0000 |
|---|---|---|
| committer | Philip Hazel <ph10@hermes.cam.ac.uk> | 2007-01-23 15:08:45 +0000 |
| commit | 6bf342e1eb87c656de34d668d7303a7d0138e89a (patch) | |
| tree | 769912c27e2b1ce420cfddf9beb0b704ffb829d6 /doc | |
| parent | 1cc59d374be28e0f2a27720d003271216676c12e (diff) | |
Installed PCRE release 7.0.
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/doc-txt/ChangeLog | 4 | ||||
| -rw-r--r-- | doc/doc-txt/pcrepattern.txt | 782 | ||||
| -rw-r--r-- | doc/doc-txt/pcretest.txt | 328 |
3 files changed, 653 insertions, 461 deletions
diff --git a/doc/doc-txt/ChangeLog b/doc/doc-txt/ChangeLog index b8795a62f..4a7f77c7a 100644 --- a/doc/doc-txt/ChangeLog +++ b/doc/doc-txt/ChangeLog @@ -1,4 +1,4 @@ -$Cambridge: exim/doc/doc-txt/ChangeLog,v 1.461 2007/01/23 14:34:02 ph10 Exp $ +$Cambridge: exim/doc/doc-txt/ChangeLog,v 1.462 2007/01/23 15:08:45 ph10 Exp $ Change log file for Exim from version 4.21 ------------------------------------------- @@ -52,6 +52,8 @@ PH/07 There was a bug in the dovecot authenticator such that the value of PH/08 Added $smtp_count_at_connection_start, deliberately with a long name. +PH/09 Installed PCRE release 7.0. + Exim version 4.66 ----------------- diff --git a/doc/doc-txt/pcrepattern.txt b/doc/doc-txt/pcrepattern.txt index 9712c86b4..f0e98e33c 100644 --- a/doc/doc-txt/pcrepattern.txt +++ b/doc/doc-txt/pcrepattern.txt @@ -1,5 +1,5 @@ This file contains the PCRE man page that describes the regular expressions -supported by PCRE version 6.7. Note that not all of the features are relevant +supported by PCRE version 7.0. Note that not all of the features are relevant in the context of Exim. In particular, the version of PCRE that is compiled with Exim does not include UTF-8 support, there is no mechanism for changing the options with which the PCRE functions are called, and features such as @@ -38,6 +38,9 @@ PCRE REGULAR EXPRESSION DETAILS function, and how it differs from the normal function, are discussed in the pcrematching page. + +CHARACTERS AND METACHARACTERS + A regular expression is a pattern that is matched against a subject string from left to right. Most characters stand for themselves in a pattern, and match the corresponding characters in the subject. As a @@ -62,8 +65,8 @@ PCRE REGULAR EXPRESSION DETAILS There are two different sets of metacharacters: those that are recog- nized anywhere in the pattern except within square brackets, and those - that are recognized in square brackets. Outside square brackets, the - metacharacters are as follows: + that are recognized within square brackets. Outside square brackets, + the metacharacters are as follows: \ general escape character with several uses ^ assert start of string (or line, in multiline mode) @@ -185,7 +188,7 @@ BACKSLASH Inside a character class, or if the decimal number is greater than 9 and there have not been that many capturing subpatterns, PCRE re-reads - up to three octal digits following the backslash, ane uses them to gen- + up to three octal digits following the backslash, and uses them to gen- erate a data character. Any subsequent digits stand for themselves. In non-UTF-8 mode, the value of a character specified in octal must be less than \400. In UTF-8 mode, values up to \777 are permitted. For @@ -212,13 +215,21 @@ BACKSLASH All the sequences that define a single character value can be used both inside and outside character classes. In addition, inside a character class, the sequence \b is interpreted as the backspace character (hex - 08), and the sequence \X is interpreted as the character "X". Outside a - character class, these sequences have different meanings (see below). + 08), and the sequences \R and \X are interpreted as the characters "R" + and "X", respectively. Outside a character class, these sequences have + different meanings (see below). + + Absolute and relative back references + + The sequence \g followed by a positive or negative number, optionally + enclosed in braces, is an absolute or relative back reference. Back + references are discussed later, following the discussion of parenthe- + sized subpatterns. Generic character types - The third use of backslash is for specifying generic character types. - The following are always recognized: + Another use of backslash is for specifying generic character types. The + following are always recognized: \d any decimal digit \D any character that is not a decimal digit @@ -255,6 +266,28 @@ BACKSLASH code character property support is available. The use of locales with Unicode is discouraged. + Newline sequences + + Outside a character class, the escape sequence \R matches any Unicode + newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is + equivalent to the following: + + (?>\r\n|\n|\x0b|\f|\r|\x85) + + This is an example of an "atomic group", details of which are given + below. This particular group matches either the two-character sequence + CR followed by LF, or one of the single characters LF (linefeed, + U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage + return, U+000D), or NEL (next line, U+0085). The two-character sequence + is treated as a single unit that cannot be split. + + In UTF-8 mode, two additional characters whose codepoints are greater + than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa- + rator, U+2029). Unicode character property support is not needed for + these characters to be recognized. + + Inside a character class, \R matches the letter "R". + Unicode character properties When PCRE is built with Unicode character property support, three addi- @@ -281,15 +314,15 @@ BACKSLASH Those that are not part of an identified script are lumped together as "Common". The current list of scripts is: - Arabic, Armenian, Bengali, Bopomofo, Braille, Buginese, Buhid, Cana- - dian_Aboriginal, Cherokee, Common, Coptic, Cypriot, Cyrillic, Deseret, - Devanagari, Ethiopic, Georgian, Glagolitic, Gothic, Greek, Gujarati, - Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana, Inherited, Kannada, - Katakana, Kharoshthi, Khmer, Lao, Latin, Limbu, Linear_B, Malayalam, - Mongolian, Myanmar, New_Tai_Lue, Ogham, Old_Italic, Old_Persian, Oriya, - Osmanya, Runic, Shavian, Sinhala, Syloti_Nagri, Syriac, Tagalog, Tag- - banwa, Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, - Ugaritic, Yi. + Arabic, Armenian, Balinese, Bengali, Bopomofo, Braille, Buginese, + Buhid, Canadian_Aboriginal, Cherokee, Common, Coptic, Cuneiform, + Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic, + Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira- + gana, Inherited, Kannada, Katakana, Kharoshthi, Khmer, Lao, Latin, + Limbu, Linear_B, Malayalam, Mongolian, Myanmar, New_Tai_Lue, Nko, + Ogham, Old_Italic, Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician, + Runic, Shavian, Sinhala, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, + Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi. Each character has exactly one general category property, specified by a two-letter abbreviation. For compatibility with Perl, negation can be @@ -382,7 +415,7 @@ BACKSLASH Simple assertions - The fourth use of backslash is for certain simple assertions. An asser- + The final use of backslash is for certain simple assertions. An asser- tion specifies a condition that has to be met at a particular point in a match, without consuming any characters from the subject string. The use of subpatterns for more complicated assertions is described below. @@ -390,10 +423,11 @@ BACKSLASH \b matches at a word boundary \B matches when not at a word boundary - \A matches at start of subject - \Z matches at end of subject or before newline at end - \z matches at end of subject - \G matches at first matching position in subject + \A matches at the start of the subject + \Z matches at the end of the subject + also matches before a newline at the end of the subject + \z matches only at the end of the subject + \G matches at the first matching position in the subject These assertions may not appear in character classes (but note that \b has a different meaning, namely the backspace character, inside a char- @@ -490,30 +524,34 @@ FULL STOP (PERIOD, DOT) Outside a character class, a dot in the pattern matches any one charac- ter in the subject string except (by default) a character that signi- fies the end of a line. In UTF-8 mode, the matched character may be - more than one byte long. When a line ending is defined as a single - character (CR or LF), dot never matches that character; when the two- - character sequence CRLF is used, dot does not match CR if it is immedi- - ately followed by LF, but otherwise it matches all characters (includ- - ing isolated CRs and LFs). - - The behaviour of dot with regard to newlines can be changed. If the - PCRE_DOTALL option is set, a dot matches any one character, without - exception. If newline is defined as the two-character sequence CRLF, it - takes two dots to match it. - - The handling of dot is entirely independent of the handling of circum- - flex and dollar, the only relationship being that they both involve + more than one byte long. + + When a line ending is defined as a single character, dot never matches + that character; when the two-character sequence CRLF is used, dot does + not match CR if it is immediately followed by LF, but otherwise it + matches all characters (including isolated CRs and LFs). When any Uni- + code line endings are being recognized, dot does not match CR or LF or + any of the other line ending characters. + + The behaviour of dot with regard to newlines can be changed. If the + PCRE_DOTALL option is set, a dot matches any one character, without + exception. If the two-character sequence CRLF is present in the subject + string, it takes two dots to match it. + + The handling of dot is entirely independent of the handling of circum- + flex and dollar, the only relationship being that they both involve newlines. Dot has no special meaning in a character class. MATCHING A SINGLE BYTE Outside a character class, the escape sequence \C matches any one byte, - both in and out of UTF-8 mode. Unlike a dot, it always matches CR and - LF. The feature is provided in Perl in order to match individual bytes - in UTF-8 mode. Because it breaks up UTF-8 characters into individual - bytes, what remains in the string may be a malformed UTF-8 string. For - this reason, the \C escape sequence is best avoided. + both in and out of UTF-8 mode. Unlike a dot, it always matches any + line-ending characters. The feature is provided in Perl in order to + match individual bytes in UTF-8 mode. Because it breaks up UTF-8 char- + acters into individual bytes, what remains in the string may be a mal- + formed UTF-8 string. For this reason, the \C escape sequence is best + avoided. PCRE does not allow \C to appear in lookbehind assertions (described below), because in UTF-8 mode this would make it impossible to calcu- @@ -560,11 +598,11 @@ SQUARE BRACKETS AND CHARACTER CLASSES PCRE is compiled with Unicode property support as well as with UTF-8 support. - Characters that might indicate line breaks (CR and LF) are never - treated in any special way when matching character classes, whatever - line-ending sequence is in use, and whatever setting of the PCRE_DOTALL - and PCRE_MULTILINE options is used. A class such as [^a] always matches - one of these characters. + Characters that might indicate line breaks are never treated in any + special way when matching character classes, whatever line-ending + sequence is in use, and whatever setting of the PCRE_DOTALL and + PCRE_MULTILINE options is used. A class such as [^a] always matches one + of these characters. The minus (hyphen) character can be used to specify a range of charac- ters in a character class. For example, [d-m] matches any letter @@ -696,26 +734,27 @@ INTERNAL OPTION SETTING PCRE extracts it into the global options (and it will therefore show up in data extracted by the pcre_fullinfo() function). - An option change within a subpattern affects only that part of the cur- - rent pattern that follows it, so + An option change within a subpattern (see below for a description of + subpatterns) affects only that part of the current pattern that follows + it, so (a(?i)b)c matches abc and aBc and no other strings (assuming PCRE_CASELESS is not - used). By this means, options can be made to have different settings - in different parts of the pattern. Any changes made in one alternative - do carry on into subsequent branches within the same subpattern. For + used). By this means, options can be made to have different settings + in different parts of the pattern. Any changes made in one alternative + do carry on into subsequent branches within the same subpattern. For example, (a(?i)b|c) - matches "ab", "aB", "c", and "C", even though when matching "C" the - first branch is abandoned before the option setting. This is because - the effects of option settings happen at compile time. There would be + matches "ab", "aB", "c", and "C", even though when matching "C" the + first branch is abandoned before the option setting. This is because + the effects of option settings happen at compile time. There would be some very weird behaviour otherwise. - The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA - can be changed in the same way as the Perl-compatible options by using + The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA + can be changed in the same way as the Perl-compatible options by using the characters J, U and X respectively. @@ -728,18 +767,18 @@ SUBPATTERNS cat(aract|erpillar|) - matches one of the words "cat", "cataract", or "caterpillar". Without - the parentheses, it would match "cataract", "erpillar" or the empty + matches one of the words "cat", "cataract", or "caterpillar". Without + the parentheses, it would match "cataract", "erpillar" or an empty string. - 2. It sets up the subpattern as a capturing subpattern. This means - that, when the whole pattern matches, that portion of the subject + 2. It sets up the subpattern as a capturing subpattern. This means + that, when the whole pattern matches, that portion of the subject string that matched the subpattern is passed back to the caller via the - ovector argument of pcre_exec(). Opening parentheses are counted from - left to right (starting from 1) to obtain numbers for the capturing + ovector argument of pcre_exec(). Opening parentheses are counted from + left to right (starting from 1) to obtain numbers for the capturing subpatterns. - For example, if the string "the red king" is matched against the pat- + For example, if the string "the red king" is matched against the pat- tern the ((red|white) (king|queen)) @@ -747,51 +786,56 @@ SUBPATTERNS the captured substrings are "red king", "red", and "king", and are num- bered 1, 2, and 3, respectively. - The fact that plain parentheses fulfil two functions is not always - helpful. There are often times when a grouping subpattern is required - without a capturing requirement. If an opening parenthesis is followed - by a question mark and a colon, the subpattern does not do any captur- - ing, and is not counted when computing the number of any subsequent - capturing subpatterns. For example, if the string "the white queen" is + The fact that plain parentheses fulfil two functions is not always + helpful. There are often times when a grouping subpattern is required + without a capturing requirement. If an opening parenthesis is followed + by a question mark and a colon, the subpattern does not do any captur- + ing, and is not counted when computing the number of any subsequent + capturing subpatterns. For example, if the string "the white queen" is matched against the pattern the ((?:red|white) (king|queen)) the captured substrings are "white queen" and "queen", and are numbered - 1 and 2. The maximum number of capturing subpatterns is 65535, and the - maximum depth of nesting of all subpatterns, both capturing and non- - capturing, is 200. + 1 and 2. The maximum number of capturing subpatterns is 65535. - As a convenient shorthand, if any option settings are required at the - start of a non-capturing subpattern, the option letters may appear + As a convenient shorthand, if any option settings are required at the + start of a non-capturing subpattern, the option letters may appear between the "?" and the ":". Thus the two patterns (?i:saturday|sunday) (?:(?i)saturday|sunday) match exactly the same set of strings. Because alternative branches are - tried from left to right, and options are not reset until the end of - the subpattern is reached, an option setting in one branch does affect - subsequent branches, so the above patterns match "SUNDAY" as well as + tried from left to right, and options are not reset until the end of + the subpattern is reached, an option setting in one branch does affect + subsequent branches, so the above patterns match "SUNDAY" as well as "Saturday". NAMED SUBPATTERNS - Identifying capturing parentheses by number is simple, but it can be - very hard to keep track of the numbers in complicated regular expres- - sions. Furthermore, if an expression is modified, the numbers may - change. To help with this difficulty, PCRE supports the naming of sub- - patterns, something that Perl does not provide. The Python syntax - (?P<name>...) is used. References to capturing parentheses from other - parts of the pattern, such as backreferences, recursion, and condi- - tions, can be made by name as well as by number. - - Names consist of up to 32 alphanumeric characters and underscores. - Named capturing parentheses are still allocated numbers as well as - names. The PCRE API provides function calls for extracting the name-to- - number translation table from a compiled pattern. There is also a con- - venience function for extracting a captured substring by name. + Identifying capturing parentheses by number is simple, but it can be + very hard to keep track of the numbers in complicated regular expres- + sions. Furthermore, if an expression is modified, the numbers may + change. To help with this difficulty, PCRE supports the naming of sub- + patterns. This feature was not added to Perl until release 5.10. Python + had the feature earlier, and PCRE introduced it at release 4.0, using + the Python syntax. PCRE now supports both the Perl and the Python syn- + tax. + + In PCRE, a subpattern can be named in one of three ways: (?<name>...) + or (?'name'...) as in Perl, or (?P<name>...) as in Python. References + to capturing parentheses from other parts of the pattern, such as back- + references, recursion, and conditions, can be made by name as well as + by number. + + Names consist of up to 32 alphanumeric characters and underscores. + Named capturing parentheses are still allocated numbers as well as + names, exactly as if the names were not present. The PCRE API provides + function calls for extracting the name-to-number translation table from + a compiled pattern. There is also a convenience function for extracting + a captured substring by name. By default, a name must be unique within a pattern, but it is possible to relax this constraint by setting the PCRE_DUPNAMES option at compile @@ -801,15 +845,15 @@ NAMED SUBPATTERNS both cases you want to extract the abbreviation. This pattern (ignoring the line breaks) does the job: - (?P<DN>Mon|Fri|Sun)(?:day)?| - (?P<DN>Tue)(?:sday)?| - (?P<DN>Wed)(?:nesday)?| - (?P<DN>Thu)(?:rsday)?| - (?P<DN>Sat)(?:urday)? + (?<DN>Mon|Fri|Sun)(?:day)?| + (?<DN>Tue)(?:sday)?| + (?<DN>Wed)(?:nesday)?| + (?<DN>Thu)(?:rsday)?| + (?<DN>Sat)(?:urday)? There are five capturing substrings, but only one is ever set after a match. The convenience function for extracting the data by name - returns the substring for the first, and in this example, the only, + returns the substring for the first (and in this example, the only) subpattern of that name that matched. This saves searching to find which numbered subpattern it was. If you make a reference to a non- unique named subpattern from elsewhere in the pattern, the one that @@ -824,9 +868,10 @@ REPETITION following items: a literal data character - the . metacharacter + the dot metacharacter the \C escape sequence the \X escape sequence (in UTF-8 mode with Unicode properties) + the \R escape sequence an escape such as \d that matches a single character a character class a back reference (see next section) @@ -866,8 +911,8 @@ REPETITION The quantifier {0} is permitted, causing the expression to behave as if the previous item and the quantifier were not present. - For convenience (and historical compatibility) the three most common - quantifiers have single-character abbreviations: + For convenience, the three most common quantifiers have single-charac- + ter abbreviations: * is equivalent to {0,} + is equivalent to {1,} @@ -919,7 +964,7 @@ REPETITION which matches one digit by preference, but can match two if that is the only way the rest of the pattern matches. - If the PCRE_UNGREEDY option is set (an option which is not available in + If the PCRE_UNGREEDY option is set (an option that is not available in Perl), the quantifiers are not greedy by default, but individual ones can be made greedy by following them with a question mark. In other words, it inverts the default behaviour. @@ -930,24 +975,25 @@ REPETITION minimum or maximum. If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv- - alent to Perl's /s) is set, thus allowing the . to match newlines, the - pattern is implicitly anchored, because whatever follows will be tried - against every character position in the subject string, so there is no - point in retrying the overall match at any position after the first. - PCRE normally treats such a pattern as though it were preceded by \A. - - In cases where it is known that the subject string contains no new- - lines, it is worth setting PCRE_DOTALL in order to obtain this opti- + alent to Perl's /s) is set, thus allowing the dot to match newlines, + the pattern is implicitly anchored, because whatever follows will be + tried against every character position in the subject string, so there + is no point in retrying the overall match at any position after the + first. PCRE normally treats such a pattern as though it were preceded + by \A. + + In cases where it is known that the subject string contains no new- + lines, it is worth setting PCRE_DOTALL in order to obtain this opti- mization, or alternatively using ^ to indicate anchoring explicitly. - However, there is one situation where the optimization cannot be used. - When .* is inside capturing parentheses that are the subject of a - backreference elsewhere in the pattern, a match at the start may fail, - and a later one succeed. Consider, for example: + However, there is one situation where the optimization cannot be used. + When .* is inside capturing parentheses that are the subject of a + backreference elsewhere in the pattern, a match at the start may fail + where a later one succeeds. Consider, for example: (.*)abc\1 - If the subject is "xyz123abc123" the match point is the fourth charac- + If the subject is "xyz123abc123" the match point is the fourth charac- ter. For this reason, such a pattern is not implicitly anchored. When a capturing subpattern is repeated, the value captured is the sub- @@ -956,8 +1002,8 @@ REPETITION (tweedle[dume]{3}\s*)+ has matched "tweedledum tweedledee" the value of the captured substring - is "tweedledee". However, if there are nested capturing subpatterns, - the corresponding captured values may have been set in previous itera- + is "tweedledee". However, if there are nested capturing subpatterns, + the corresponding captured values may have been set in previous itera- tions. For example, after /(a|(b))+/ @@ -967,12 +1013,13 @@ REPETITION ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS - With both maximizing and minimizing repetition, failure of what follows - normally causes the repeated item to be re-evaluated to see if a dif- - ferent number of repeats allows the rest of the pattern to match. Some- - times it is useful to prevent this, either to change the nature of the - match, or to cause it fail earlier than it otherwise might, when the - author of the pattern knows there is no point in carrying on. + With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy") + repetition, failure of what follows normally causes the repeated item + to be re-evaluated to see if a different number of repeats allows the + rest of the pattern to match. Sometimes it is useful to prevent this, + either to change the nature of the match, or to cause it fail earlier + than it otherwise might, when the author of the pattern knows there is + no point in carrying on. Consider, for example, the pattern \d+foo when applied to the subject line @@ -986,10 +1033,9 @@ ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS the means for specifying that once a subpattern has matched, it is not to be re-evaluated in this way. - If we use atomic grouping for the previous example, the matcher would - give up immediately on failing to match "foo" the first time. The nota- - tion is a kind of special parenthesis, starting with (?> as in this - example: + If we use atomic grouping for the previous example, the matcher gives + up immediately on failing to match "foo" the first time. The notation + is a kind of special parenthesis, starting with (?> as in this example: (?>\d+)foo @@ -1021,63 +1067,95 @@ ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS Possessive quantifiers are always greedy; the setting of the PCRE_UNGREEDY option is ignored. They are a convenient notation for the simpler forms of atomic group. However, there is no difference in the - meaning or processing of a possessive quantifier and the equivalent - atomic group. - - The possessive quantifier syntax is an extension to the Perl syntax. - Jeffrey Friedl originated the idea (and the name) in the first edition - of his book. Mike McCloskey liked it, so implemented it when he built - Sun's Java package, and PCRE copied it from there. - - When a pattern contains an unlimited repeat inside a subpattern that - can itself be repeated an unlimited number of times, the use of an - atomic group is the only way to avoid some failing matches taking a + meaning of a possessive quantifier and the equivalent atomic group, + though there may be a performance difference; possessive quantifiers + should be slightly faster. + + The possessive quantifier syntax is an extension to the Perl 5.8 syn- + tax. Jeffrey Friedl originated the idea (and the name) in the first + edition of his book. Mike McCloskey liked it, so implemented it when he + built Sun's Java package, and PCRE copied it from there. It ultimately + found its way into Perl at release 5.10. + + PCRE has an optimization that automatically "possessifies" certain sim- + ple pattern constructs. For example, the sequence A+B is treated as + A++B because there is no point in backtracking into a sequence of A's + when B must follow. + + When a pattern contains an unlimited repeat inside a subpattern that + can itself be repeated an unlimited number of times, the use of an + atomic group is the only way to avoid some failing matches taking a very long time indeed. The pattern (\D+|<\d+>)*[!?] - matches an unlimited number of substrings that either consist of non- - digits, or digits enclosed in <>, followed by either ! or ?. When it + matches an unlimited number of substrings that either consist of non- + digits, or digits enclosed in <>, followed by either ! or ?. When it matches, it runs quickly. However, if it is applied to aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa - it takes a long time before reporting failure. This is because the - string can be divided between the internal \D+ repeat and the external - * repeat in a large number of ways, and all have to be tried. (The - example uses [!?] rather than a single character at the end, because - both PCRE and Perl have an optimization that allows for fast failure - when a single character is used. They remember the last single charac- - ter that is required for a match, and fail early if it is not present - in the string.) If the pattern is changed so that it uses an atomic + it takes a long time before reporting failure. This is because the + string can be divided between the internal \D+ repeat and the external + * repeat in a large number of ways, and all have to be tried. (The + example uses [!?] rather than a single character at the end, because + both PCRE and Perl have an optimization that allows for fast failure + when a single character is used. They remember the last single charac- + ter that is required for a match, and fail early if it is not present + in the string.) If the pattern is changed so that it uses an atomic group, like this: ((?>\D+)|<\d+>)*[!?] - sequences of non-digits cannot be broken, and failure happens quickly. + sequences of non-digits cannot be broken, and failure happens quickly. BACK REFERENCES Outside a character class, a backslash followed by a digit greater than 0 (and possibly further digits) is a back reference to a capturing sub- - pattern earlier (that is, to its left) in the pattern, provided there + pattern earlier (that is, to its left) in the pattern, provided there have been that many previous capturing left parentheses. However, if the decimal number following the backslash is less than 10, - it is always taken as a back reference, and causes an error only if - there are not that many capturing left parentheses in the entire pat- - tern. In other words, the parentheses that are referenced need not be - to the left of the reference for numbers less than 10. A "forward back - reference" of this type can make sense when a repetition is involved - and the subpattern to the right has participated in an earlier itera- + it is always taken as a back reference, and causes an error only if + there are not that many capturing left parentheses in the entire pat- + tern. In other words, the parentheses that are referenced need not be + to the left of the reference for numbers less than 10. A "forward back + reference" of this type can make sense when a repetition is involved + and the subpattern to the right has participated in an earlier itera- tion. - It is not possible to have a numerical "forward back reference" to sub- - pattern whose number is 10 or more. However, a back reference to any - subpattern is possible using named parentheses (see below). See also - the subsection entitled "Non-printing characters" above for further - details of the handling of digits following a backslash. + It is not possible to have a numerical "forward back reference" to a + subpattern whose number is 10 or more using this syntax because a + sequence such as \50 is interpreted as a character defined in octal. + See the subsection entitled "Non-printing characters" above for further + details of the handling of digits following a backslash. There is no + such problem when named parentheses are used. A back reference to any + subpattern is possible using named parentheses (see below). + + Another way of avoiding the ambiguity inherent in the use of digits + following a backslash is to use the \g escape sequence, which is a fea- + ture introduced in Perl 5.10. This escape must be followed by a posi- + tive or a negative number, optionally enclosed in braces. These exam- + ples are all identical: + + (ring), \1 + (ring), \g1 + (ring), \g{1} + + A positive number specifies an absolute reference without the ambiguity + that is present in the older syntax. It is also useful when literal + digits follow the reference. A negative number is a relative reference. + Consider this example: + + (abc(def)ghi)\g{-1} + + The sequence \g{-1} is a reference to the most recently started captur- + ing subpattern before \g, that is, is it equivalent to \2. Similarly, + \g{-2} would be equivalent to \1. The use of relative references can be + helpful in long patterns, and also in patterns that are created by + joining together fragments that contain references within themselves. A back reference matches whatever actually matched the capturing sub- pattern in the current subject string, rather than anything matching @@ -1096,62 +1174,64 @@ BACK REFERENCES matches "rah rah" and "RAH RAH", but not "RAH rah", even though the original capturing subpattern is matched caselessly. - Back references to named subpatterns use the Python syntax (?P=name). - We could rewrite the above example as follows: + Back references to named subpatterns use the Perl syntax \k<name> or + \k'name' or the Python syntax (?P=name). We could rewrite the above + example in either of the following ways: + (?<p1>(?i)rah)\s+\k<p1> (?P<p1>(?i)rah)\s+(?P=p1) - A subpattern that is referenced by name may appear in the pattern + A subpattern that is referenced by name may appear in the pattern before or after the reference. - There may be more than one back reference to the same subpattern. If a - subpattern has not actually been used in a particular match, any back + There may be more than one back reference to the same subpattern. If a + subpattern has not actually been used in a particular match, any back references to it always fail. For example, the pattern (a|(bc))\2 - always fails if it starts to match "a" rather than "bc". Because there - may be many capturing parentheses in a pattern, all digits following - the backslash are taken as part of a potential back reference number. + always fails if it starts to match "a" rather than "bc". Because there + may be many capturing parentheses in a pattern, all digits following + the backslash are taken as part of a potential back reference number. If the pattern continues with a digit character, some delimiter must be - used to terminate the back reference. If the PCRE_EXTENDED option is - set, this can be whitespace. Otherwise an empty comment (see "Com- + used to terminate the back reference. If the PCRE_EXTENDED option is + set, this can be whitespace. Otherwise an empty comment (see "Com- ments" below) can be used. - A back reference that occurs inside the parentheses to which it refers - fails when the subpattern is first used, so, for example, (a\1) never - matches. However, such references can be useful inside repeated sub- + A back reference that occurs inside the parentheses to which it refers + fails when the subpattern is first used, so, for example, (a\1) never + matches. However, such references can be useful inside repeated sub- patterns. For example, the pattern (a|b\1)+ matches any number of "a"s and also "aba", "ababbaa" etc. At each iter- - ation of the subpattern, the back reference matches the character - string corresponding to the previous iteration. In order for this to - work, the pattern must be such that the first iteration does not need - to match the back reference. This can be done using alternation, as in + ation of the subpattern, the back reference matches the character + string corresponding to the previous iteration. In order for this to + work, the pattern must be such that the first iteration does not need + to match the back reference. This can be done using alternation, as in the example above, or by a quantifier with a minimum of zero. ASSERTIONS - An assertion is a test on the characters following or preceding the - current matching point that does not actually consume any characters. - The simple assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are + An assertion is a test on the characters following or preceding the + current matching point that does not actually consume any characters. + The simple assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are described above. - More complicated assertions are coded as subpatterns. There are two - kinds: those that look ahead of the current position in the subject - string, and those that look behind it. An assertion subpattern is - matched in the normal way, except that it does not cause the current + More complicated assertions are coded as subpatterns. There are two + kinds: those that look ahead of the current position in the subject + string, and those that look behind it. An assertion subpattern is + matched in the normal way, except that it does not cause the current matching position to be changed. - Assertion subpatterns are not capturing subpatterns, and may not be - repeated, because it makes no sense to assert the same thing several - times. If any kind of assertion contains capturing subpatterns within - it, these are counted for the purposes of numbering the capturing sub- + Assertion subpatterns are not capturing subpatterns, and may not be + repeated, because it makes no sense to assert the same thing several + times. If any kind of assertion contains capturing subpatterns within + it, these are counted for the purposes of numbering the capturing sub- patterns in the whole pattern. However, substring capturing is carried - out only for positive assertions, because it does not make sense for + out only for positive assertions, because it does not make sense for negative assertions. Lookahead assertions @@ -1161,37 +1241,37 @@ ASSERTIONS \w+(?=;) - matches a word followed by a semicolon, but does not include the semi- + matches a word followed by a semicolon, but does not include the semi- colon in the match, and foo(?!bar) - matches any occurrence of "foo" that is not followed by "bar". Note + matches any occurrence of "foo" that is not followed by "bar". Note that the apparently similar pattern (?!foo)bar - does not find an occurrence of "bar" that is preceded by something - other than "foo"; it finds any occurrence of "bar" whatsoever, because + does not find an occurrence of "bar" that is preceded by something + other than "foo"; it finds any occurrence of "bar" whatsoever, because the assertion (?!foo) is always true when the next three characters are "bar". A lookbehind assertion is needed to achieve the other effect. If you want to force a matching failure at some point in a pattern, the - most convenient way to do it is with (?!) because an empty string - always matches, so an assertion that requires there not to be an empty + most convenient way to do it is with (?!) because an empty string + always matches, so an assertion that requires there not to be an empty string must always fail. Lookbehind assertions - Lookbehind assertions start with (?<= for positive assertions and (?<! + Lookbehind assertions start with (?<= for positive assertions and (?<! for negative assertions. For example, (?<!foo)bar - does find an occurrence of "bar" that is not preceded by "foo". The - contents of a lookbehind assertion are restricted such that all the + does find an occurrence of "bar" that is not preceded by "foo". The + contents of a lookbehind assertion are restricted such that all the strings it matches must have a fixed length. However, if there are sev- - eral top-level alternatives, they do not all have to have the same + eral top-level alternatives, they do not all have to have the same fixed length. Thus (?<=bullock|donkey) @@ -1200,59 +1280,55 @@ ASSERTIONS (?<!dogs?|cats?) - causes an error at compile time. Branches that match different length - strings are permitted only at the top level of a lookbehind assertion. - This is an extension compared with Perl (at least for 5.8), which - requires all branches to match the same length of string. An assertion + causes an error at compile time. Branches that match different length + strings are permitted only at the top level of a lookbehind assertion. + This is an extension compared with Perl (at least for 5.8), which + requires all branches to match the same length of string. An assertion such as (?<=ab(c|de)) - is not permitted, because its single top-level branch can match two - different lengths, but it is acceptable if rewritten to use two top- + is not permitted, because its single top-level branch can match two + different lengths, but it is acceptable if rewritten to use two top- level branches: (?<=abc|abde) - The implementation of lookbehind assertions is, for each alternative, - to temporarily move the current position back by the fixed width and + The implementation of lookbehind assertions is, for each alternative, + to temporarily move the current position back by the fixed length and then try to match. If there are insufficient characters before the cur- - rent position, the match is deemed to fail. + rent position, the assertion fails. PCRE does not allow the \C escape (which matches a single byte in UTF-8 - mode) to appear in lookbehind assertions, because it makes it impossi- - ble to calculate the length of the lookbehind. The \X escape, which can - match different numbers of bytes, is also not permitted. + mode) to appear in lookbehind assertions, because it makes it impossi- + ble to calculate the length of the lookbehind. The \X and \R escapes, + which can match different numbers of bytes, are also not permitted. - Atomic groups can be used in conjunction with lookbehind assertions to - specify efficient matching at the end of the subject string. Consider a - simple pattern such as + Possessive quantifiers can be used in conjunction with lookbehind + assertions to specify efficient matching at the end of the subject + string. Consider a simple pattern such as abcd$ - when applied to a long string that does not match. Because matching + when applied to a long string that does not match. Because matching proceeds from left to right, PCRE will look for each "a" in the subject - and then see if what follows matches the rest of the pattern. If the + and then see if what follows matches the rest of the pattern. If the pattern is specified as ^.*abcd$ - the initial .* matches the entire string at first, but when this fails + the initial .* matches the entire string at first, but when this fails (because there is no following "a"), it backtracks to match all but the - last character, then all but the last two characters, and so on. Once - again the search for "a" covers the entire string, from right to left, + last character, then all but the last two characters, and so on. Once + again the search for "a" covers the entire string, from right to left, so we are no better off. However, if the pattern is written as - ^(?>.*)(?<=abcd) - - or, equivalently, using the possessive quantifier syntax, - ^.*+(?<=abcd) - there can be no backtracking for the .* item; it can match only the - entire string. The subsequent lookbehind assertion does a single test - on the last four characters. If it fails, the match fails immediately. - For long strings, this approach makes a significant difference to the + there can be no backtracking for the .*+ item; it can match only the + entire string. The subsequent lookbehind assertion does a single test + on the last four characters. If it fails, the match fails immediately. + For long strings, this approach makes a significant difference to the processing time. Using multiple assertions @@ -1261,18 +1337,18 @@ ASSERTIONS (?<=\d{3})(?<!999)foo - matches "foo" preceded by three digits that are not "999". Notice that - each of the assertions is applied independently at the same point in - the subject string. First there is a check that the previous three - characters are all digits, and then there is a check that the same + matches "foo" preceded by three digits that are not "999". Notice that + each of the assertions is applied independently at the same point in + the subject string. First there is a check that the previous three + characters are all digits, and then there is a check that the same three characters are not "999". This pattern does not match "foo" pre- - ceded by six characters, the first of which are digits and the last - three of which are not "999". For example, it doesn't match "123abc- + ceded by six characters, the first of which are digits and the last + three of which are not "999". For example, it doesn't match "123abc- foo". A pattern to do that is (?<=\d{3}...)(?<!999)foo - This time the first assertion looks at the preceding six characters, + This time the first assertion looks at the preceding six characters, checking that the first three are digits, and then the second assertion checks that the preceding three characters are not "999". @@ -1280,39 +1356,38 @@ ASSERTIONS (?<=(?<!foo)bar)baz - matches an occurrence of "baz" that is preceded by "bar" which in turn + matches an occurrence of "baz" that is preceded by "bar" which in turn is not preceded by "foo", while (?<=\d{3}(?!999)...)foo - is another pattern that matches "foo" preceded by three digits and any + is another pattern that matches "foo" preceded by three digits and any three characters that are not "999". CONDITIONAL SUBPATTERNS - It is possible to cause the matching process to obey a subpattern con- - ditionally or to choose between two alternative subpatterns, depending - on the result of an assertion, or whether a previous capturing subpat- - tern matched or not. The two possible forms of conditional subpattern + It is possible to cause the matching process to obey a subpattern con- + ditionally or to choose between two alternative subpatterns, depending + on the result of an assertion, or whether a previous capturing subpat- + tern matched or not. The two possible forms of conditional subpattern are (?(condition)yes-pattern) (?(condition)yes-pattern|no-pattern) - If the condition is satisfied, the yes-pattern is used; otherwise the - no-pattern (if present) is used. If there are more than two alterna- + If the condition is satisfied, the yes-pattern is used; otherwise the + no-pattern (if present) is used. If there are more than two alterna- tives in the subpattern, a compile-time error occurs. - There are three kinds of condition. If the text between the parentheses - consists of a sequence of digits, or a sequence of alphanumeric charac- - ters and underscores, the condition is satisfied if the capturing sub- - pattern of that number or name has previously matched. There is a pos- - sible ambiguity here, because subpattern names may consist entirely of - digits. PCRE looks first for a named subpattern; if it cannot find one - and the text consists entirely of digits, it looks for a subpattern of - that number, which must be greater than zero. Using subpattern names - that consist entirely of digits is not recommended. + There are four kinds of condition: references to subpatterns, refer- + ences to recursion, a pseudo-condition called DEFINE, and assertions. + + Checking for a used subpattern by number + + If the text between the parentheses consists of a sequence of digits, + the condition is true if the capturing subpattern of that number has + previously matched. Consider the following pattern, which contains non-significant white space to make it more readable (assume the PCRE_EXTENDED option) and to @@ -1329,18 +1404,68 @@ CONDITIONAL SUBPATTERNS tern is executed and a closing parenthesis is required. Otherwise, since no-pattern is not present, the subpattern matches nothing. In other words, this pattern matches a sequence of non-parentheses, - optionally enclosed in parentheses. Rewriting it to use a named subpat- - tern gives this: + optionally enclosed in parentheses. + + Checking for a used subpattern by name + + Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a + used subpattern by name. For compatibility with earlier versions of + PCRE, which had this facility before Perl, the syntax (?(name)...) is + also recognized. However, there is a possible ambiguity with this syn- + tax, because subpattern names may consist entirely of digits. PCRE + looks first for a named subpattern; if it cannot find one and the name + consists entirely of digits, PCRE looks for a subpattern of that num- + ber, which must be greater than zero. Using subpattern names that con- + sist entirely of digits is not recommended. + + Rewriting the above example to use a named subpattern gives this: - (?P<OPEN> \( )? [^()]+ (?(OPEN) \) ) + (?<OPEN> \( )? [^()]+ (?(<OPEN>) \) ) + + + Checking for pattern recursion If the condition is the string (R), and there is no subpattern with the - name R, the condition is satisfied if a recursive call to the pattern - or subpattern has been made. At "top level", the condition is false. - This is a PCRE extension. Recursive patterns are described in the next - section. + name R, the condition is true if a recursive call to the whole pattern + or any subpattern has been made. If digits or a name preceded by amper- + sand follow the letter R, for example: + + (?(R3)...) or (?(R&name)...) + + the condition is true if the most recent recursion is into the subpat- + tern whose number or name is given. This condition does not check the + entire recursion stack. + + At "top level", all these recursion test conditions are false. Recur- + sive patterns are described below. + + Defining subpatterns for use by reference only + + If the condition is the string (DEFINE), and there is no subpattern + with the name DEFINE, the condition is always false. In this case, + there may be only one alternative in the subpattern. It is always + skipped if control reaches this point in the pattern; the idea of + DEFINE is that it can be used to define "subroutines" that can be ref- + erenced from elsewhere. (The use of "subroutines" is described below.) + For example, a pattern to match an IPv4 address could be written like + this (ignore whitespace and line breaks): + + (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) ) + \b (?&byte) (\.(?&byte)){3} \b + + The first part of the pattern is a DEFINE group inside which a another + group named "byte" is defined. This matches an individual component of + an IPv4 address (a number less than 256). When matching takes place, + this part of the pattern is skipped because DEFINE acts like a false + condition. + + The rest of the pattern uses references to the named group to match the + four dot-separated components of an IPv4 address, insisting on a word + boundary at each end. - If the condition is not a sequence of digits or (R), it must be an + Assertion conditions + + If the condition is not in any of the above formats, it must be an assertion. This may be a positive or negative lookahead or lookbehind assertion. Consider this pattern, again containing non-significant white space, and with the two alternatives on the second line: @@ -1375,110 +1500,116 @@ RECURSIVE PATTERNS unlimited nested parentheses. Without the use of recursion, the best that can be done is to use a pattern that matches up to some fixed depth of nesting. It is not possible to handle an arbitrary nesting - depth. Perl provides a facility that allows regular expressions to - recurse (amongst other things). It does this by interpolating Perl code - in the expression at run time, and the code can refer to the expression - itself. A Perl pattern to solve the parentheses problem can be created - like this: + depth. + + For some time, Perl has provided a facility that allows regular expres- + sions to recurse (amongst other things). It does this by interpolating + Perl code in the expression at run time, and the code can refer to the + expression itself. A Perl pattern using code interpolation to solve the + parentheses problem can be created like this: $re = qr{\( (?: (?>[^()]+) | (?p{$re}) )* \)}x; The (?p{...}) item interpolates Perl code at run time, and in this case - refers recursively to the pattern in which it appears. Obviously, PCRE - cannot support the interpolation of Perl code. Instead, it supports - some special syntax for recursion of the entire pattern, and also for - individual subpattern recursion. + refers recursively to the pattern in which it appears. + + Obviously, PCRE cannot support the interpolation of Perl code. Instead, + it supports special syntax for recursion of the entire pattern, and + also for individual subpattern recursion. After its introduction in + PCRE and Python, this kind of recursion was introduced into Perl at + release 5.10. - The special item that consists of (? followed by a number greater than + A special item that consists of (? followed by a number greater than zero and a closing parenthesis is a recursive call of the subpattern of - the given number, provided that it occurs inside that subpattern. (If - not, it is a "subroutine" call, which is described in the next sec- - tion.) The special item (?R) is a recursive call of the entire regular - expression. + the given number, provided that it occurs inside that subpattern. (If + not, it is a "subroutine" call, which is described in the next sec- + tion.) The special item (?R) or (?0) is a recursive call of the entire + regular expression. - A recursive subpattern call is always treated as an atomic group. That - is, once it has matched some of the subject string, it is never re- - entered, even if it contains untried alternatives and there is a subse- - quent matching failure. + In PCRE (like Python, but unlike Perl), a recursive subpattern call is + always treated as an atomic group. That is, once it has matched some of + the subject string, it is never re-entered, even if it contains untried + alternatives and there is a subsequent matching failure. - This PCRE pattern solves the nested parentheses problem (assume the + This PCRE pattern solves the nested parentheses problem (assume the PCRE_EXTENDED option is set so that white space is ignored): \( ( (?>[^()]+) | (?R) )* \) - First it matches an opening parenthesis. Then it matches any number of - substrings which can either be a sequence of non-parentheses, or a - recursive match of the pattern itself (that is, a correctly parenthe- + First it matches an opening parenthesis. Then it matches any number of + substrings which can either be a sequence of non-parentheses, or a + recursive match of the pattern itself (that is, a correctly parenthe- sized substring). Finally there is a closing parenthesis. - If this were part of a larger pattern, you would not want to recurse + If this were part of a larger pattern, you would not want to recurse the entire pattern, so instead you could use this: ( \( ( (?>[^()]+) | (?1) )* \) ) - We have put the pattern into parentheses, and caused the recursion to - refer to them instead of the whole pattern. In a larger pattern, keep- - ing track of parenthesis numbers can be tricky. It may be more conve- - nient to use named parentheses instead. For this, PCRE uses (?P>name), - which is an extension to the Python syntax that PCRE uses for named - parentheses (Perl does not provide named parentheses). We could rewrite - the above example as follows: + We have put the pattern into parentheses, and caused the recursion to + refer to them instead of the whole pattern. In a larger pattern, keep- + ing track of parenthesis numbers can be tricky. It may be more conve- + nient to use named parentheses instead. The Perl syntax for this is + (?&name); PCRE's earlier syntax (?P>name) is also supported. We could + rewrite the above example as follows: - (?P<pn> \( ( (?>[^()]+) | (?P>pn) )* \) ) + (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) ) - This particular example pattern contains nested unlimited repeats, and - so the use of atomic grouping for matching strings of non-parentheses - is important when applying the pattern to strings that do not match. - For example, when this pattern is applied to + If there is more than one subpattern with the same name, the earliest + one is used. This particular example pattern contains nested unlimited + repeats, and so the use of atomic grouping for matching strings of non- + parentheses is important when applying the pattern to strings that do + not match. For example, when this pattern is applied to (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa() - it yields "no match" quickly. However, if atomic grouping is not used, - the match runs for a very long time indeed because there are so many - different ways the + and * repeats can carve up the subject, and all + it yields "no match" quickly. However, if atomic grouping is not used, + the match runs for a very long time indeed because there are so many + different ways the + and * repeats can carve up the subject, and all have to be tested before failure can be reported. At the end of a match, the values set for any capturing subpatterns are those from the outermost level of the recursion at which the subpattern - value is set. If you want to obtain intermediate values, a callout - function can be used (see the next section and the pcrecallout documen- - tation). If the pattern above is matched against + value is set. If you want to obtain intermediate values, a callout + function can be used (see below and the pcrecallout documentation). If + the pattern above is matched against (ab(cd)ef) - the value for the capturing parentheses is "ef", which is the last - value taken on at the top level. If additional parentheses are added, + the value for the capturing parentheses is "ef", which is the last + value taken on at the top level. If additional parentheses are added, giving \( ( ( (?>[^()]+) | (?R) )* ) \) ^ ^ ^ ^ - the string they capture is "ab(cd)ef", the contents of the top level - parentheses. If there are more than 15 capturing parentheses in a pat- + the string they capture is "ab(cd)ef", the contents of the top level + parentheses. If there are more than 15 capturing parentheses in a pat- tern, PCRE has to obtain extra memory to store data during a recursion, - which it does by using pcre_malloc, freeing it via pcre_free after- - wards. If no memory can be obtained, the match fails with the + which it does by using pcre_malloc, freeing it via pcre_free after- + wards. If no memory can be obtained, the match fails with the PCRE_ERROR_NOMEMORY error. - Do not confuse the (?R) item with the condition (R), which tests for - recursion. Consider this pattern, which matches text in angle brack- - ets, allowing for arbitrary nesting. Only digits are allowed in nested - brackets (that is, when recursing), whereas any characters are permit- + Do not confuse the (?R) item with the condition (R), which tests for + recursion. Consider this pattern, which matches text in angle brack- + ets, allowing for arbitrary nesting. Only digits are allowed in nested + brackets (that is, when recursing), whereas any characters are permit- ted at the outer level. < (?: (?(R) \d++ | [^<>]*+) | (?R)) * > - In this pattern, (?(R) is the start of a conditional subpattern, with - two different alternatives for the recursive and non-recursive cases. + In this pattern, (?(R) is the start of a conditional subpattern, with + two different alternatives for the recursive and non-recursive cases. The (?R) item is the actual recursive call. SUBPATTERNS AS SUBROUTINES If the syntax for a recursive subpattern reference (either by number or - by name) is used outside the parentheses to which it refers, it oper- - ates like a subroutine in a programming language. An earlier example + by name) is used outside the parentheses to which it refers, it oper- + ates like a subroutine in a programming language. The "called" subpat- + tern may be defined before or after the reference. An earlier example pointed out that the pattern (sens|respons)e and \1ibility @@ -1489,15 +1620,23 @@ SUBPATTERNS AS SUBROUTINES (sens|respons)e and (?1)ibility is used, it does match "sense and responsibility" as well as the other - two strings. Such references, if given numerically, must follow the - subpattern to which they refer. However, named references can refer to - later subpatterns. + two strings. Another example is given in the discussion of DEFINE + above. Like recursive subpatterns, a "subroutine" call is always treated as an - atomic group. That is, once it has matched some of the subject string, - it is never re-entered, even if it contains untried alternatives and + atomic group. That is, once it has matched some of the subject string, + it is never re-entered, even if it contains untried alternatives and there is a subsequent matching failure. + When a subpattern is used as a subroutine, processing options such as + case-independence are fixed when the subpattern is defined. They cannot + be changed for different calls. For example, consider this pattern: + + (abc)(?i:(?1)) + + It matches "abcabc". It does not match "abcABC" because the change of + processing option does not affect the called subpattern. + CALLOUTS @@ -1533,5 +1672,10 @@ CALLOUTS gether. A complete description of the interface to the callout function is given in the pcrecallout documentation. -Last updated: 06 June 2006 + +SEE ALSO + + pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3). + +Last updated: 06 December 2006 Copyright (c) 1997-2006 University of Cambridge. diff --git a/doc/doc-txt/pcretest.txt b/doc/doc-txt/pcretest.txt index dfa03b80b..1a0424c20 100644 --- a/doc/doc-txt/pcretest.txt +++ b/doc/doc-txt/pcretest.txt @@ -24,18 +24,24 @@ SYNOPSIS OPTIONS + -b Behave as if each regex has the /B (show bytecode) modifier; + the internal form is output after compilation. + -C Output the version number of the PCRE library, and all avail- - able information about the optional features that are + able information about the optional features that are included, and then exit. - -d Behave as if each regex has the /D (debug) modifier; the - internal form is output after compilation. + -d Behave as if each regex has the /D (debug) modifier; the + internal form and information about the compiled pattern is + output after compilation; -d is equivalent to -b -i. -dfa Behave as if each data line contains the \D escape sequence; this causes the alternative matching function, pcre_dfa_exec(), to be used instead of the standard pcre_exec() function (more detail is given below). + -help Output a brief summary these options and then exit. + -i Behave as if each regex has the /I modifier; information about the compiled pattern is given after compilation. @@ -45,10 +51,12 @@ OPTIONS pcretest, -s is a synonym for -m. -o osize Set the number of elements in the output vector that is used - when calling pcre_exec() to be osize. The default value is - 45, which is enough for 14 capturing subexpressions. The vec- - tor size can be changed for individual matching calls by - including \O in the data line (see below). + when calling pcre_exec() or pcre_dfa_exec() to be osize. The + default value is 45, which is enough for 14 capturing subex- + pressions for pcre_exec() or 22 different matches for + pcre_dfa_exec(). The vector size can be changed for individ- + ual matching calls by including \O in the data line (see + below). -p Behave as if each regex has the /P modifier; the POSIX wrap- per API is used to call PCRE. None of the other options has @@ -64,7 +72,13 @@ OPTIONS and output resulting time per compile or match (in millisec- onds). Do not set -m with -t, because you will then get the size output a zillion times, and the timing will be dis- - torted. + torted. You can control the number of iterations that are + used for timing by following -t with a number (as a separate + item on the command line). For example, "-t 1000" would iter- + ate 1000 times. The default is to iterate 500000 times. + + -tm This is like -t except that it times only the matching phase, + not the compile or study phases. DESCRIPTION @@ -82,53 +96,54 @@ DESCRIPTION Each data line is matched separately and independently. If you want to do multi-line matches, you have to use the \n escape sequence (or \r or - \r\n, depending on the newline setting) in a single line of input to - encode the newline characters. There is no limit on the length of data - lines; the input buffer is automatically extended if it is too small. + \r\n, etc., depending on the newline setting) in a single line of input + to encode the newline sequences. There is no limit on the length of + data lines; the input buffer is automatically extended if it is too + small. - An empty line signals the end of the data lines, at which point a new - regular expression is read. The regular expressions are given enclosed + An empty line signals the end of the data lines, at which point a new + regular expression is read. The regular expressions are given enclosed in any non-alphanumeric delimiters other than backslash, for example: /(a|bc)x+yz/ - White space before the initial delimiter is ignored. A regular expres- - sion may be continued over several input lines, in which case the new- - line characters are included within it. It is possible to include the + White space before the initial delimiter is ignored. A regular expres- + sion may be continued over several input lines, in which case the new- + line characters are included within it. It is possible to include the delimiter within the pattern by escaping it, for example /abc\/def/ - If you do so, the escape and the delimiter form part of the pattern, - but since delimiters are always non-alphanumeric, this does not affect - its interpretation. If the terminating delimiter is immediately fol- + If you do so, the escape and the delimiter form part of the pattern, + but since delimiters are always non-alphanumeric, this does not affect + its interpretation. If the terminating delimiter is immediately fol- lowed by a backslash, for example, /abc/\ - then a backslash is added to the end of the pattern. This is done to - provide a way of testing the error condition that arises if a pattern + then a backslash is added to the end of the pattern. This is done to + provide a way of testing the error condition that arises if a pattern finishes with a backslash, because /abc\/ - is interpreted as the first line of a pattern that starts with "abc/", + is interpreted as the first line of a pattern that starts with "abc/", causing pcretest to read the next line as a continuation of the regular expression. PATTERN MODIFIERS - A pattern may be followed by any number of modifiers, which are mostly - single characters. Following Perl usage, these are referred to below - as, for example, "the /i modifier", even though the delimiter of the - pattern need not always be a slash, and no slash is used when writing - modifiers. Whitespace may appear between the final pattern delimiter + A pattern may be followed by any number of modifiers, which are mostly + single characters. Following Perl usage, these are referred to below + as, for example, "the /i modifier", even though the delimiter of the + pattern need not always be a slash, and no slash is used when writing + modifiers. Whitespace may appear between the final pattern delimiter and the first modifier, and between the modifiers themselves. The /i, /m, /s, and /x modifiers set the PCRE_CASELESS, PCRE_MULTILINE, - PCRE_DOTALL, or PCRE_EXTENDED options, respectively, when pcre_com- - pile() is called. These four modifier letters have the same effect as + PCRE_DOTALL, or PCRE_EXTENDED options, respectively, when pcre_com- + pile() is called. These four modifier letters have the same effect as they do in Perl. For example: /caseless/i @@ -147,10 +162,16 @@ PATTERN MODIFIERS /<cr> PCRE_NEWLINE_CR /<lf> PCRE_NEWLINE_LF /<crlf> PCRE_NEWLINE_CRLF + /<any> PCRE_NEWLINE_ANY + + Those specifying line ending sequencess are literal strings as shown. + This example sets multiline matching with CRLF as the line ending + sequence: - Those specifying line endings are literal strings as shown. Details of - the meanings of these PCRE options are given in the pcreapi documenta- - tion. + /^abc/m<crlf> + + Details of the meanings of these PCRE options are given in the pcreapi + documentation. Finding all matches in a string @@ -180,79 +201,80 @@ PATTERN MODIFIERS remainder of the subject string. This is useful for tests where the subject contains multiple copies of the same substring. - The /L modifier must be followed directly by the name of a locale, for + The /B modifier is a debugging feature. It requests that pcretest out- + put a representation of the compiled byte code after compilation. + + The /L modifier must be followed directly by the name of a locale, for example, /pattern/Lfr_FR For this reason, it must be the last modifier. The given locale is set, - pcre_maketables() is called to build a set of character tables for the - locale, and this is then passed to pcre_compile() when compiling the - regular expression. Without an /L modifier, NULL is passed as the - tables pointer; that is, /L applies only to the expression on which it + pcre_maketables() is called to build a set of character tables for the + locale, and this is then passed to pcre_compile() when compiling the + regular expression. Without an /L modifier, NULL is passed as the + tables pointer; that is, /L applies only to the expression on which it appears. - The /I modifier requests that pcretest output information about the - compiled pattern (whether it is anchored, has a fixed first character, - and so on). It does this by calling pcre_fullinfo() after compiling a - pattern. If the pattern is studied, the results of that are also out- + The /I modifier requests that pcretest output information about the + compiled pattern (whether it is anchored, has a fixed first character, + and so on). It does this by calling pcre_fullinfo() after compiling a + pattern. If the pattern is studied, the results of that are also out- put. - The /D modifier is a PCRE debugging feature, which also assumes /I. It - causes the internal form of compiled regular expressions to be output - after compilation. If the pattern was studied, the information returned - is also output. + The /D modifier is a PCRE debugging feature, and is equivalent to /BI, + that is, both the /B and the /I modifiers. The /F modifier causes pcretest to flip the byte order of the fields in - the compiled pattern that contain 2-byte and 4-byte numbers. This - facility is for testing the feature in PCRE that allows it to execute + the compiled pattern that contain 2-byte and 4-byte numbers. This + facility is for testing the feature in PCRE that allows it to execute patterns that were compiled on a host with a different endianness. This - feature is not available when the POSIX interface to PCRE is being - used, that is, when the /P pattern modifier is specified. See also the + feature is not available when the POSIX interface to PCRE is being + used, that is, when the /P pattern modifier is specified. See also the section about saving and reloading compiled patterns below. - The /S modifier causes pcre_study() to be called after the expression + The /S modifier causes pcre_study() to be called after the expression has been compiled, and the results used when the expression is matched. - The /M modifier causes the size of memory block used to hold the com- + The /M modifier causes the size of memory block used to hold the com- piled pattern to be output. - The /P modifier causes pcretest to call PCRE via the POSIX wrapper API - rather than its native API. When this is done, all other modifiers - except /i, /m, and /+ are ignored. REG_ICASE is set if /i is present, - and REG_NEWLINE is set if /m is present. The wrapper functions force - PCRE_DOLLAR_ENDONLY always, and PCRE_DOTALL unless REG_NEWLINE is set. + The /P modifier causes pcretest to call PCRE via the POSIX wrapper API + rather than its native API. When this is done, all other modifiers + except /i, /m, and /+ are ignored. REG_ICASE is set if /i is present, + and REG_NEWLINE is set if /m is present. The wrapper functions force + PCRE_DOLLAR_ENDONLY always, and PCRE_DOTALL unless REG_NEWLINE is set. - The /8 modifier causes pcretest to call PCRE with the PCRE_UTF8 option - set. This turns on support for UTF-8 character handling in PCRE, pro- - vided that it was compiled with this support enabled. This modifier + The /8 modifier causes pcretest to call PCRE with the PCRE_UTF8 option + set. This turns on support for UTF-8 character handling in PCRE, pro- + vided that it was compiled with this support enabled. This modifier also causes any non-printing characters in output strings to be printed using the \x{hh...} notation if they are valid UTF-8 sequences. - If the /? modifier is used with /8, it causes pcretest to call - pcre_compile() with the PCRE_NO_UTF8_CHECK option, to suppress the + If the /? modifier is used with /8, it causes pcretest to call + pcre_compile() with the PCRE_NO_UTF8_CHECK option, to suppress the checking of the string for UTF-8 validity. DATA LINES - Before each data line is passed to pcre_exec(), leading and trailing - whitespace is removed, and it is then scanned for \ escapes. Some of - these are pretty esoteric features, intended for checking out some of - the more complicated features of PCRE. If you are just testing "ordi- - nary" regular expressions, you probably don't need any of these. The + Before each data line is passed to pcre_exec(), leading and trailing + whitespace is removed, and it is then scanned for \ escapes. Some of + these are pretty esoteric features, intended for checking out some of + the more complicated features of PCRE. If you are just testing "ordi- + nary" regular expressions, you probably don't need any of these. The following escapes are recognized: - \a alarm (= BEL) - \b backspace - \e escape - \f formfeed - \n newline + \a alarm (BEL, \x07) + \b backspace (\x08) + \e escape (\x27) + \f formfeed (\x0c) + \n newline (\x0a) \qdd set the PCRE_MATCH_LIMIT limit to dd (any number of digits) - \r carriage return - \t tab - \v vertical tab + \r carriage return (\x0d) + \t tab (\x09) + \v vertical tab (\x0b) \nnn octal character (up to 3 octal digits) \xhh hexadecimal character (up to 2 hex digits) \x{hh...} hexadecimal character, any number of digits @@ -309,12 +331,17 @@ DATA LINES or pcre_dfa_exec() \<crlf> pass the PCRE_NEWLINE_CRLF option to pcre_exec() or pcre_dfa_exec() + \<any> pass the PCRE_NEWLINE_ANY option to pcre_exec() + or pcre_dfa_exec() - The escapes that specify line endings are literal strings, exactly as - shown. A backslash followed by anything else just escapes the anything - else. If the very last character is a backslash, it is ignored. This - gives a way of passing an empty line as data, since a real empty line - terminates the data input. + The escapes that specify line ending sequences are literal strings, + exactly as shown. No more than one newline setting should be present in + any data line. + + A backslash followed by anything else just escapes the anything else. + If the very last character is a backslash, it is ignored. This gives a + way of passing an empty line as data, since a real empty line termi- + nates the data input. If \M is present, pcretest calls pcre_exec() several times, with dif- ferent values in the match_limit and match_limit_recursion fields of @@ -371,7 +398,7 @@ DEFAULT OUTPUT FROM PCRETEST is an example of an interactive pcretest run. $ pcretest - PCRE version 5.00 07-Sep-2004 + PCRE version 7.0 30-Nov-2006 re> /^abc(\d+)/ data> abc123 @@ -382,16 +409,17 @@ DEFAULT OUTPUT FROM PCRETEST If the strings contain any non-printing characters, they are output as \0x escapes, or as \x{...} escapes if the /8 modifier was present on - the pattern. If the pattern has the /+ modifier, the output for sub- - string 0 is followed by the the rest of the subject string, identified - by "0+" like this: + the pattern. See below for the definition of non-printing characters. + If the pattern has the /+ modifier, the output for substring 0 is fol- + lowed by the the rest of the subject string, identified by "0+" like + this: re> /cat/+ data> cataract 0: cat 0+ aract - If the pattern has the /g or /G modifier, the results of successive + If the pattern has the /g or /G modifier, the results of successive matching attempts are output in sequence, like this: re> /\Bi(\w\w)/g @@ -405,24 +433,24 @@ DEFAULT OUTPUT FROM PCRETEST "No match" is output only if the first match attempt fails. - If any of the sequences \C, \G, or \L are present in a data line that - is successfully matched, the substrings extracted by the convenience + If any of the sequences \C, \G, or \L are present in a data line that + is successfully matched, the substrings extracted by the convenience functions are output with C, G, or L after the string number instead of a colon. This is in addition to the normal full list. The string length - (that is, the return from the extraction function) is given in paren- + (that is, the return from the extraction function) is given in paren- theses after each string for \C and \G. - Note that while patterns can be continued over several lines (a plain + Note that whereas patterns can be continued over several lines (a plain ">" prompt is used for continuations), data lines may not. However new- - lines can be included in data by means of the \n escape (or \r or \r\n - for those newline settings). + lines can be included in data by means of the \n escape (or \r, \r\n, + etc., depending on the newline sequence setting). OUTPUT FROM THE ALTERNATIVE MATCHING FUNCTION - When the alternative matching function, pcre_dfa_exec(), is used (by - means of the \D escape sequence or the -dfa command line option), the - output consists of a list of all the matches that start at the first + When the alternative matching function, pcre_dfa_exec(), is used (by + means of the \D escape sequence or the -dfa command line option), the + output consists of a list of all the matches that start at the first point in the subject where there is at least one match. For example: re> /(tang|tangerine|tan)/ @@ -431,11 +459,11 @@ OUTPUT FROM THE ALTERNATIVE MATCHING FUNCTION 1: tang 2: tan - (Using the normal matching function on this data finds only "tang".) - The longest matching string is always given first (and numbered zero). + (Using the normal matching function on this data finds only "tang".) + The longest matching string is always given first (and numbered zero). - If /gP is present on the pattern, the search for further matches - resumes at the end of the longest match. For example: + If /g is present on the pattern, the search for further matches resumes + at the end of the longest match. For example: re> /(tang|tangerine|tan)/g data> yellow tangerine and tangy sultana\D @@ -446,16 +474,16 @@ OUTPUT FROM THE ALTERNATIVE MATCHING FUNCTION 1: tan 0: tan - Since the matching function does not support substring capture, the - escape sequences that are concerned with captured substrings are not + Since the matching function does not support substring capture, the + escape sequences that are concerned with captured substrings are not relevant. RESTARTING AFTER A PARTIAL MATCH When the alternative matching function has given the PCRE_ERROR_PARTIAL - return, indicating that the subject partially matched the pattern, you - can restart the match with additional subject data by means of the \R + return, indicating that the subject partially matched the pattern, you + can restart the match with additional subject data by means of the \R escape sequence. For example: re> /^?(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)$/ @@ -464,30 +492,30 @@ RESTARTING AFTER A PARTIAL MATCH data> n05\R\D 0: n05 - For further information about partial matching, see the pcrepartial + For further information about partial matching, see the pcrepartial documentation. CALLOUTS - If the pattern contains any callout requests, pcretest's callout func- - tion is called during matching. This works with both matching func- + If the pattern contains any callout requests, pcretest's callout func- + tion is called during matching. This works with both matching func- tions. By default, the called function displays the callout number, the - start and current positions in the text at the callout time, and the + start and current positions in the text at the callout time, and the next pattern item to be tested. For example, the output --->pqrabcdef 0 ^ ^ \d - indicates that callout number 0 occurred for a match attempt starting - at the fourth character of the subject string, when the pointer was at - the seventh character of the data, and when the next pattern item was - \d. Just one circumflex is output if the start and current positions + indicates that callout number 0 occurred for a match attempt starting + at the fourth character of the subject string, when the pointer was at + the seventh character of the data, and when the next pattern item was + \d. Just one circumflex is output if the start and current positions are the same. Callouts numbered 255 are assumed to be automatic callouts, inserted as - a result of the /C pattern modifier. In this case, instead of showing - the callout number, the offset in the pattern, preceded by a plus, is + a result of the /C pattern modifier. In this case, instead of showing + the callout number, the offset in the pattern, preceded by a plus, is output. For example: re> /\d?[A-E]\*/C @@ -499,76 +527,94 @@ CALLOUTS +10 ^ ^ 0: E* - The callout function in pcretest returns zero (carry on matching) by - default, but you can use a \C item in a data line (as described above) + The callout function in pcretest returns zero (carry on matching) by + default, but you can use a \C item in a data line (as described above) to change this. - Inserting callouts can be helpful when using pcretest to check compli- - cated regular expressions. For further information about callouts, see + Inserting callouts can be helpful when using pcretest to check compli- + cated regular expressions. For further information about callouts, see the pcrecallout documentation. +NON-PRINTING CHARACTERS + + When pcretest is outputting text in the compiled version of a pattern, + bytes other than 32-126 are always treated as non-printing characters + are are therefore shown as hex escapes. + + When pcretest is outputting text that is a matched part of a subject + string, it behaves in the same way, unless a different locale has been + set for the pattern (using the /L modifier). In this case, the + isprint() function to distinguish printing and non-printing characters. + + SAVING AND RELOADING COMPILED PATTERNS - The facilities described in this section are not available when the + The facilities described in this section are not available when the POSIX inteface to PCRE is being used, that is, when the /P pattern mod- ifier is specified. When the POSIX interface is not in use, you can cause pcretest to write - a compiled pattern to a file, by following the modifiers with > and a + a compiled pattern to a file, by following the modifiers with > and a file name. For example: /pattern/im >/some/file - See the pcreprecompile documentation for a discussion about saving and + See the pcreprecompile documentation for a discussion about saving and re-using compiled patterns. - The data that is written is binary. The first eight bytes are the - length of the compiled pattern data followed by the length of the - optional study data, each written as four bytes in big-endian order - (most significant byte first). If there is no study data (either the + The data that is written is binary. The first eight bytes are the + length of the compiled pattern data followed by the length of the + optional study data, each written as four bytes in big-endian order + (most significant byte first). If there is no study data (either the pattern was not studied, or studying did not return any data), the sec- - ond length is zero. The lengths are followed by an exact copy of the + ond length is zero. The lengths are followed by an exact copy of the compiled pattern. If there is additional study data, this follows imme- - diately after the compiled pattern. After writing the file, pcretest + diately after the compiled pattern. After writing the file, pcretest expects to read a new pattern. A saved pattern can be reloaded into pcretest by specifing < and a file - name instead of a pattern. The name of the file must not contain a < - character, as otherwise pcretest will interpret the line as a pattern + name instead of a pattern. The name of the file must not contain a < + character, as otherwise pcretest will interpret the line as a pattern delimited by < characters. For example: re> </some/file Compiled regex loaded from /some/file No study data - When the pattern has been loaded, pcretest proceeds to read data lines + When the pattern has been loaded, pcretest proceeds to read data lines in the usual way. - You can copy a file written by pcretest to a different host and reload - it there, even if the new host has opposite endianness to the one on - which the pattern was compiled. For example, you can compile on an i86 + You can copy a file written by pcretest to a different host and reload + it there, even if the new host has opposite endianness to the one on + which the pattern was compiled. For example, you can compile on an i86 machine and run on a SPARC machine. - File names for saving and reloading can be absolute or relative, but - note that the shell facility of expanding a file name that starts with + File names for saving and reloading can be absolute or relative, but + note that the shell facility of expanding a file name that starts with a tilde (~) is not available. - The ability to save and reload files in pcretest is intended for test- - ing and experimentation. It is not intended for production use because - only a single pattern can be written to a file. Furthermore, there is - no facility for supplying custom character tables for use with a - reloaded pattern. If the original pattern was compiled with custom - tables, an attempt to match a subject string using a reloaded pattern - is likely to cause pcretest to crash. Finally, if you attempt to load + The ability to save and reload files in pcretest is intended for test- + ing and experimentation. It is not intended for production use because + only a single pattern can be written to a file. Furthermore, there is + no facility for supplying custom character tables for use with a + reloaded pattern. If the original pattern was compiled with custom + tables, an attempt to match a subject string using a reloaded pattern + is likely to cause pcretest to crash. Finally, if you attempt to load a file that is not in the correct format, the result is undefined. +SEE ALSO + + pcre(3), pcreapi(3), pcrecallout(3), pcrematching(3), pcrepartial(d), + pcrepattern(3), pcreprecompile(3). + + AUTHOR Philip Hazel University Computing Service, - Cambridge CB2 3QG, England. + Cambridge CB2 3QH, England. -Last updated: 29 June 2006 +Last updated: 30 November 2006 Copyright (c) 1997-2006 University of Cambridge. |