Documentation update.
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Philip.Hazel
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@ -3176,14 +3176,23 @@ A name is always required with this verb. There may be as many instances of
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(*MARK) as you like in a pattern, and their names do not have to be unique.
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(*MARK) as you like in a pattern, and their names do not have to be unique.
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</P>
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</P>
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<P>
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<P>
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When a match succeeds, the name of the last-encountered (*MARK:NAME),
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When a match succeeds, the name of the last-encountered (*MARK:NAME) on the
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(*PRUNE:NAME), or (*THEN:NAME) on the matching path is passed back to the
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matching path is passed back to the caller as described in the section entitled
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caller as described in the section entitled
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<a href="pcre2api.html#matchotherdata">"Other information about the match"</a>
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<a href="pcre2api.html#matchotherdata">"Other information about the match"</a>
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in the
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in the
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<a href="pcre2api.html"><b>pcre2api</b></a>
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<a href="pcre2api.html"><b>pcre2api</b></a>
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documentation. Here is an example of <b>pcre2test</b> output, where the "mark"
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documentation. This applies to all instances of (*MARK), including those inside
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modifier requests the retrieval and outputting of (*MARK) data:
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assertions and atomic groups. (There are differences in those cases when
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(*MARK) is used in conjunction with (*SKIP) as described below.)
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</P>
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<P>
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As well as (*MARK), the (*PRUNE) and (*THEN) verbs may have associated NAME
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arguments. Whichever is last on the matching path is passed back. See below for
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more details of these other verbs.
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</P>
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<P>
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Here is an example of <b>pcre2test</b> output, where the "mark" modifier
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requests the retrieval and outputting of (*MARK) data:
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<pre>
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<pre>
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re> /X(*MARK:A)Y|X(*MARK:B)Z/mark
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re> /X(*MARK:A)Y|X(*MARK:B)Z/mark
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data> XY
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data> XY
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@ -3344,14 +3353,14 @@ following <b>pcre2test</b> examples:
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0: b
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0: b
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1: b
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1: b
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</pre>
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</pre>
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In the first example, the (*MARK) setting is in an atomic group, so it is not
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In the first example, the (*MARK) setting is in an atomic group, so it is not
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seen when (*SKIP:X) triggers, causing the (*SKIP) to be ignored. This allows
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seen when (*SKIP:X) triggers, causing the (*SKIP) to be ignored. This allows
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the second branch of the pattern to be tried at the first character position.
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the second branch of the pattern to be tried at the first character position.
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In the second example, the (*MARK) setting is not in an atomic group. This
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In the second example, the (*MARK) setting is not in an atomic group. This
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allows (*SKIP:X) to immediately cause a new matching attempt to start at the
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allows (*SKIP:X) to find the (*MARK) when it backtracks, and this causes a new
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second character. This time, the (*MARK) is never seen because "a" does not
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matching attempt to start at the second character. This time, the (*MARK) is
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match "b", so the matcher immediately jumps to the second branch of the
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never seen because "a" does not match "b", so the matcher immediately jumps to
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pattern.
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the second branch of the pattern.
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</P>
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</P>
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<P>
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<P>
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Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It ignores
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Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It ignores
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@ -3542,7 +3551,7 @@ Cambridge, England.
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</P>
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</P>
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<br><a name="SEC30" href="#TOC1">REVISION</a><br>
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<br><a name="SEC30" href="#TOC1">REVISION</a><br>
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<P>
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<P>
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Last updated: 11 July 2018
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Last updated: 16 July 2018
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<br>
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<br>
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Copyright © 1997-2018 University of Cambridge.
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Copyright © 1997-2018 University of Cambridge.
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<br>
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<br>
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163
doc/pcre2.txt
163
doc/pcre2.txt
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@ -8651,12 +8651,20 @@ BACKTRACKING CONTROL
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instances of (*MARK) as you like in a pattern, and their names do not
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instances of (*MARK) as you like in a pattern, and their names do not
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have to be unique.
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have to be unique.
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When a match succeeds, the name of the last-encountered (*MARK:NAME),
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When a match succeeds, the name of the last-encountered (*MARK:NAME) on
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(*PRUNE:NAME), or (*THEN:NAME) on the matching path is passed back to
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the matching path is passed back to the caller as described in the sec-
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the caller as described in the section entitled "Other information
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tion entitled "Other information about the match" in the pcre2api docu-
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about the match" in the pcre2api documentation. Here is an example of
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mentation. This applies to all instances of (*MARK), including those
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pcre2test output, where the "mark" modifier requests the retrieval and
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inside assertions and atomic groups. (There are differences in those
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outputting of (*MARK) data:
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cases when (*MARK) is used in conjunction with (*SKIP) as described
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below.)
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As well as (*MARK), the (*PRUNE) and (*THEN) verbs may have associated
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NAME arguments. Whichever is last on the matching path is passed back.
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See below for more details of these other verbs.
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Here is an example of pcre2test output, where the "mark" modifier
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requests the retrieval and outputting of (*MARK) data:
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re> /X(*MARK:A)Y|X(*MARK:B)Z/mark
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re> /X(*MARK:A)Y|X(*MARK:B)Z/mark
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data> XY
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data> XY
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@ -8816,171 +8824,172 @@ BACKTRACKING CONTROL
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is not seen when (*SKIP:X) triggers, causing the (*SKIP) to be ignored.
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is not seen when (*SKIP:X) triggers, causing the (*SKIP) to be ignored.
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This allows the second branch of the pattern to be tried at the first
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This allows the second branch of the pattern to be tried at the first
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character position. In the second example, the (*MARK) setting is not
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character position. In the second example, the (*MARK) setting is not
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in an atomic group. This allows (*SKIP:X) to immediately cause a new
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in an atomic group. This allows (*SKIP:X) to find the (*MARK) when it
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matching attempt to start at the second character. This time, the
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backtracks, and this causes a new matching attempt to start at the sec-
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(*MARK) is never seen because "a" does not match "b", so the matcher
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ond character. This time, the (*MARK) is never seen because "a" does
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immediately jumps to the second branch of the pattern.
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not match "b", so the matcher immediately jumps to the second branch of
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the pattern.
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Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It
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Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It
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ignores names that are set by (*PRUNE:NAME) or (*THEN:NAME).
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ignores names that are set by (*PRUNE:NAME) or (*THEN:NAME).
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(*THEN) or (*THEN:NAME)
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(*THEN) or (*THEN:NAME)
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This verb causes a skip to the next innermost alternative when back-
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This verb causes a skip to the next innermost alternative when back-
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tracking reaches it. That is, it cancels any further backtracking
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tracking reaches it. That is, it cancels any further backtracking
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within the current alternative. Its name comes from the observation
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within the current alternative. Its name comes from the observation
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that it can be used for a pattern-based if-then-else block:
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that it can be used for a pattern-based if-then-else block:
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( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
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( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
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If the COND1 pattern matches, FOO is tried (and possibly further items
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If the COND1 pattern matches, FOO is tried (and possibly further items
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after the end of the group if FOO succeeds); on failure, the matcher
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after the end of the group if FOO succeeds); on failure, the matcher
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skips to the second alternative and tries COND2, without backtracking
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skips to the second alternative and tries COND2, without backtracking
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into COND1. If that succeeds and BAR fails, COND3 is tried. If subse-
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into COND1. If that succeeds and BAR fails, COND3 is tried. If subse-
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quently BAZ fails, there are no more alternatives, so there is a back-
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quently BAZ fails, there are no more alternatives, so there is a back-
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track to whatever came before the entire group. If (*THEN) is not
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track to whatever came before the entire group. If (*THEN) is not
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inside an alternation, it acts like (*PRUNE).
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inside an alternation, it acts like (*PRUNE).
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The behaviour of (*THEN:NAME) is the not the same as
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The behaviour of (*THEN:NAME) is the not the same as
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(*MARK:NAME)(*THEN). It is like (*MARK:NAME) in that the name is
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(*MARK:NAME)(*THEN). It is like (*MARK:NAME) in that the name is
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remembered for passing back to the caller. However, (*SKIP:NAME)
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remembered for passing back to the caller. However, (*SKIP:NAME)
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searches only for names set with (*MARK), ignoring those set by
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searches only for names set with (*MARK), ignoring those set by
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(*PRUNE) and (*THEN).
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(*PRUNE) and (*THEN).
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A subpattern that does not contain a | character is just a part of the
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A subpattern that does not contain a | character is just a part of the
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enclosing alternative; it is not a nested alternation with only one
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enclosing alternative; it is not a nested alternation with only one
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alternative. The effect of (*THEN) extends beyond such a subpattern to
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alternative. The effect of (*THEN) extends beyond such a subpattern to
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the enclosing alternative. Consider this pattern, where A, B, etc. are
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the enclosing alternative. Consider this pattern, where A, B, etc. are
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complex pattern fragments that do not contain any | characters at this
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complex pattern fragments that do not contain any | characters at this
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level:
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level:
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A (B(*THEN)C) | D
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A (B(*THEN)C) | D
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If A and B are matched, but there is a failure in C, matching does not
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If A and B are matched, but there is a failure in C, matching does not
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backtrack into A; instead it moves to the next alternative, that is, D.
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backtrack into A; instead it moves to the next alternative, that is, D.
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However, if the subpattern containing (*THEN) is given an alternative,
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However, if the subpattern containing (*THEN) is given an alternative,
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it behaves differently:
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it behaves differently:
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A (B(*THEN)C | (*FAIL)) | D
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A (B(*THEN)C | (*FAIL)) | D
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The effect of (*THEN) is now confined to the inner subpattern. After a
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The effect of (*THEN) is now confined to the inner subpattern. After a
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failure in C, matching moves to (*FAIL), which causes the whole subpat-
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failure in C, matching moves to (*FAIL), which causes the whole subpat-
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tern to fail because there are no more alternatives to try. In this
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tern to fail because there are no more alternatives to try. In this
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case, matching does now backtrack into A.
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case, matching does now backtrack into A.
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Note that a conditional subpattern is not considered as having two
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Note that a conditional subpattern is not considered as having two
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alternatives, because only one is ever used. In other words, the |
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alternatives, because only one is ever used. In other words, the |
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character in a conditional subpattern has a different meaning. Ignoring
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character in a conditional subpattern has a different meaning. Ignoring
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white space, consider:
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white space, consider:
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^.*? (?(?=a) a | b(*THEN)c )
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^.*? (?(?=a) a | b(*THEN)c )
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If the subject is "ba", this pattern does not match. Because .*? is
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If the subject is "ba", this pattern does not match. Because .*? is
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ungreedy, it initially matches zero characters. The condition (?=a)
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ungreedy, it initially matches zero characters. The condition (?=a)
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then fails, the character "b" is matched, but "c" is not. At this
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then fails, the character "b" is matched, but "c" is not. At this
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point, matching does not backtrack to .*? as might perhaps be expected
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point, matching does not backtrack to .*? as might perhaps be expected
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from the presence of the | character. The conditional subpattern is
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from the presence of the | character. The conditional subpattern is
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part of the single alternative that comprises the whole pattern, and so
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part of the single alternative that comprises the whole pattern, and so
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the match fails. (If there was a backtrack into .*?, allowing it to
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the match fails. (If there was a backtrack into .*?, allowing it to
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match "b", the match would succeed.)
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match "b", the match would succeed.)
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The verbs just described provide four different "strengths" of control
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The verbs just described provide four different "strengths" of control
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when subsequent matching fails. (*THEN) is the weakest, carrying on the
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when subsequent matching fails. (*THEN) is the weakest, carrying on the
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match at the next alternative. (*PRUNE) comes next, failing the match
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match at the next alternative. (*PRUNE) comes next, failing the match
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at the current starting position, but allowing an advance to the next
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at the current starting position, but allowing an advance to the next
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character (for an unanchored pattern). (*SKIP) is similar, except that
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character (for an unanchored pattern). (*SKIP) is similar, except that
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the advance may be more than one character. (*COMMIT) is the strongest,
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the advance may be more than one character. (*COMMIT) is the strongest,
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causing the entire match to fail.
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causing the entire match to fail.
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More than one backtracking verb
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More than one backtracking verb
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If more than one backtracking verb is present in a pattern, the one
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If more than one backtracking verb is present in a pattern, the one
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that is backtracked onto first acts. For example, consider this pat-
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that is backtracked onto first acts. For example, consider this pat-
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tern, where A, B, etc. are complex pattern fragments:
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tern, where A, B, etc. are complex pattern fragments:
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(A(*COMMIT)B(*THEN)C|ABD)
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(A(*COMMIT)B(*THEN)C|ABD)
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If A matches but B fails, the backtrack to (*COMMIT) causes the entire
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If A matches but B fails, the backtrack to (*COMMIT) causes the entire
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match to fail. However, if A and B match, but C fails, the backtrack to
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match to fail. However, if A and B match, but C fails, the backtrack to
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(*THEN) causes the next alternative (ABD) to be tried. This behaviour
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(*THEN) causes the next alternative (ABD) to be tried. This behaviour
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is consistent, but is not always the same as Perl's. It means that if
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is consistent, but is not always the same as Perl's. It means that if
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two or more backtracking verbs appear in succession, all the the last
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two or more backtracking verbs appear in succession, all the the last
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of them has no effect. Consider this example:
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of them has no effect. Consider this example:
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...(*COMMIT)(*PRUNE)...
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...(*COMMIT)(*PRUNE)...
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If there is a matching failure to the right, backtracking onto (*PRUNE)
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If there is a matching failure to the right, backtracking onto (*PRUNE)
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causes it to be triggered, and its action is taken. There can never be
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causes it to be triggered, and its action is taken. There can never be
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a backtrack onto (*COMMIT).
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a backtrack onto (*COMMIT).
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Backtracking verbs in repeated groups
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Backtracking verbs in repeated groups
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PCRE2 differs from Perl in its handling of backtracking verbs in
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PCRE2 differs from Perl in its handling of backtracking verbs in
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repeated groups. For example, consider:
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repeated groups. For example, consider:
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/(a(*COMMIT)b)+ac/
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/(a(*COMMIT)b)+ac/
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If the subject is "abac", Perl matches, but PCRE2 fails because the
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If the subject is "abac", Perl matches, but PCRE2 fails because the
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(*COMMIT) in the second repeat of the group acts.
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(*COMMIT) in the second repeat of the group acts.
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Backtracking verbs in assertions
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Backtracking verbs in assertions
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(*FAIL) in any assertion has its normal effect: it forces an immediate
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(*FAIL) in any assertion has its normal effect: it forces an immediate
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backtrack. The behaviour of the other backtracking verbs depends on
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backtrack. The behaviour of the other backtracking verbs depends on
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whether or not the assertion is standalone or acting as the condition
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whether or not the assertion is standalone or acting as the condition
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in a conditional subpattern.
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in a conditional subpattern.
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(*ACCEPT) in a standalone positive assertion causes the assertion to
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(*ACCEPT) in a standalone positive assertion causes the assertion to
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succeed without any further processing; captured strings are retained.
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succeed without any further processing; captured strings are retained.
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In a standalone negative assertion, (*ACCEPT) causes the assertion to
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In a standalone negative assertion, (*ACCEPT) causes the assertion to
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fail without any further processing; captured substrings are discarded.
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fail without any further processing; captured substrings are discarded.
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If the assertion is a condition, (*ACCEPT) causes the condition to be
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If the assertion is a condition, (*ACCEPT) causes the condition to be
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true for a positive assertion and false for a negative one; captured
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true for a positive assertion and false for a negative one; captured
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substrings are retained in both cases.
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substrings are retained in both cases.
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The remaining verbs act only when a later failure causes a backtrack to
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The remaining verbs act only when a later failure causes a backtrack to
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reach them. This means that their effect is confined to the assertion,
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reach them. This means that their effect is confined to the assertion,
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because lookaround assertions are atomic. A backtrack that occurs after
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because lookaround assertions are atomic. A backtrack that occurs after
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an assertion is complete does not jump back into the assertion. Note in
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an assertion is complete does not jump back into the assertion. Note in
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particular that a (*MARK) name that is set in an assertion is not
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particular that a (*MARK) name that is set in an assertion is not
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"seen" by an instance of (*SKIP:NAME) latter in the pattern.
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"seen" by an instance of (*SKIP:NAME) latter in the pattern.
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The effect of (*THEN) is not allowed to escape beyond an assertion. If
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The effect of (*THEN) is not allowed to escape beyond an assertion. If
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there are no more branches to try, (*THEN) causes a positive assertion
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there are no more branches to try, (*THEN) causes a positive assertion
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to be false, and a negative assertion to be true.
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to be false, and a negative assertion to be true.
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The other backtracking verbs are not treated specially if they appear
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The other backtracking verbs are not treated specially if they appear
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in a standalone positive assertion. In a conditional positive asser-
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in a standalone positive assertion. In a conditional positive asser-
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tion, backtracking (from within the assertion) into (*COMMIT), (*SKIP),
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tion, backtracking (from within the assertion) into (*COMMIT), (*SKIP),
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or (*PRUNE) causes the condition to be false. However, for both stand-
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or (*PRUNE) causes the condition to be false. However, for both stand-
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alone and conditional negative assertions, backtracking into (*COMMIT),
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alone and conditional negative assertions, backtracking into (*COMMIT),
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(*SKIP), or (*PRUNE) causes the assertion to be true, without consider-
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(*SKIP), or (*PRUNE) causes the assertion to be true, without consider-
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ing any further alternative branches.
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ing any further alternative branches.
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Backtracking verbs in subroutines
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Backtracking verbs in subroutines
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These behaviours occur whether or not the subpattern is called recur-
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These behaviours occur whether or not the subpattern is called recur-
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sively. Perl's treatment of subroutines is different in some cases.
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sively. Perl's treatment of subroutines is different in some cases.
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(*FAIL) in a subpattern called as a subroutine has its normal effect:
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(*FAIL) in a subpattern called as a subroutine has its normal effect:
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it forces an immediate backtrack.
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it forces an immediate backtrack.
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(*ACCEPT) in a subpattern called as a subroutine causes the subroutine
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(*ACCEPT) in a subpattern called as a subroutine causes the subroutine
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match to succeed without any further processing. Matching then contin-
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match to succeed without any further processing. Matching then contin-
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ues after the subroutine call.
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ues after the subroutine call.
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(*COMMIT), (*SKIP), and (*PRUNE) in a subpattern called as a subroutine
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(*COMMIT), (*SKIP), and (*PRUNE) in a subpattern called as a subroutine
|
||||||
cause the subroutine match to fail.
|
cause the subroutine match to fail.
|
||||||
|
|
||||||
(*THEN) skips to the next alternative in the innermost enclosing group
|
(*THEN) skips to the next alternative in the innermost enclosing group
|
||||||
within the subpattern that has alternatives. If there is no such group
|
within the subpattern that has alternatives. If there is no such group
|
||||||
within the subpattern, (*THEN) causes the subroutine match to fail.
|
within the subpattern, (*THEN) causes the subroutine match to fail.
|
||||||
|
|
||||||
|
|
||||||
SEE ALSO
|
SEE ALSO
|
||||||
|
|
||||||
pcre2api(3), pcre2callout(3), pcre2matching(3), pcre2syntax(3),
|
pcre2api(3), pcre2callout(3), pcre2matching(3), pcre2syntax(3),
|
||||||
pcre2(3).
|
pcre2(3).
|
||||||
|
|
||||||
|
|
||||||
|
|
@ -8993,7 +9002,7 @@ AUTHOR
|
||||||
|
|
||||||
REVISION
|
REVISION
|
||||||
|
|
||||||
Last updated: 11 July 2018
|
Last updated: 16 July 2018
|
||||||
Copyright (c) 1997-2018 University of Cambridge.
|
Copyright (c) 1997-2018 University of Cambridge.
|
||||||
------------------------------------------------------------------------------
|
------------------------------------------------------------------------------
|
||||||
|
|
||||||
|
|
|
||||||
|
|
@ -1,4 +1,4 @@
|
||||||
.TH PCRE2PATTERN 3 "11 July 2018" "PCRE2 10.32"
|
.TH PCRE2PATTERN 3 "16 July 2018" "PCRE2 10.32"
|
||||||
.SH NAME
|
.SH NAME
|
||||||
PCRE2 - Perl-compatible regular expressions (revised API)
|
PCRE2 - Perl-compatible regular expressions (revised API)
|
||||||
.SH "PCRE2 REGULAR EXPRESSION DETAILS"
|
.SH "PCRE2 REGULAR EXPRESSION DETAILS"
|
||||||
|
|
@ -3206,9 +3206,8 @@ starting point (see (*SKIP) below).
|
||||||
A name is always required with this verb. There may be as many instances of
|
A name is always required with this verb. There may be as many instances of
|
||||||
(*MARK) as you like in a pattern, and their names do not have to be unique.
|
(*MARK) as you like in a pattern, and their names do not have to be unique.
|
||||||
.P
|
.P
|
||||||
When a match succeeds, the name of the last-encountered (*MARK:NAME),
|
When a match succeeds, the name of the last-encountered (*MARK:NAME) on the
|
||||||
(*PRUNE:NAME), or (*THEN:NAME) on the matching path is passed back to the
|
matching path is passed back to the caller as described in the section entitled
|
||||||
caller as described in the section entitled
|
|
||||||
.\" HTML <a href="pcre2api.html#matchotherdata">
|
.\" HTML <a href="pcre2api.html#matchotherdata">
|
||||||
.\" </a>
|
.\" </a>
|
||||||
"Other information about the match"
|
"Other information about the match"
|
||||||
|
|
@ -3217,8 +3216,16 @@ in the
|
||||||
.\" HREF
|
.\" HREF
|
||||||
\fBpcre2api\fP
|
\fBpcre2api\fP
|
||||||
.\"
|
.\"
|
||||||
documentation. Here is an example of \fBpcre2test\fP output, where the "mark"
|
documentation. This applies to all instances of (*MARK), including those inside
|
||||||
modifier requests the retrieval and outputting of (*MARK) data:
|
assertions and atomic groups. (There are differences in those cases when
|
||||||
|
(*MARK) is used in conjunction with (*SKIP) as described below.)
|
||||||
|
.P
|
||||||
|
As well as (*MARK), the (*PRUNE) and (*THEN) verbs may have associated NAME
|
||||||
|
arguments. Whichever is last on the matching path is passed back. See below for
|
||||||
|
more details of these other verbs.
|
||||||
|
.P
|
||||||
|
Here is an example of \fBpcre2test\fP output, where the "mark" modifier
|
||||||
|
requests the retrieval and outputting of (*MARK) data:
|
||||||
.sp
|
.sp
|
||||||
re> /X(*MARK:A)Y|X(*MARK:B)Z/mark
|
re> /X(*MARK:A)Y|X(*MARK:B)Z/mark
|
||||||
data> XY
|
data> XY
|
||||||
|
|
@ -3374,14 +3381,14 @@ following \fBpcre2test\fP examples:
|
||||||
0: b
|
0: b
|
||||||
1: b
|
1: b
|
||||||
.sp
|
.sp
|
||||||
In the first example, the (*MARK) setting is in an atomic group, so it is not
|
In the first example, the (*MARK) setting is in an atomic group, so it is not
|
||||||
seen when (*SKIP:X) triggers, causing the (*SKIP) to be ignored. This allows
|
seen when (*SKIP:X) triggers, causing the (*SKIP) to be ignored. This allows
|
||||||
the second branch of the pattern to be tried at the first character position.
|
the second branch of the pattern to be tried at the first character position.
|
||||||
In the second example, the (*MARK) setting is not in an atomic group. This
|
In the second example, the (*MARK) setting is not in an atomic group. This
|
||||||
allows (*SKIP:X) to immediately cause a new matching attempt to start at the
|
allows (*SKIP:X) to find the (*MARK) when it backtracks, and this causes a new
|
||||||
second character. This time, the (*MARK) is never seen because "a" does not
|
matching attempt to start at the second character. This time, the (*MARK) is
|
||||||
match "b", so the matcher immediately jumps to the second branch of the
|
never seen because "a" does not match "b", so the matcher immediately jumps to
|
||||||
pattern.
|
the second branch of the pattern.
|
||||||
.P
|
.P
|
||||||
Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It ignores
|
Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It ignores
|
||||||
names that are set by (*PRUNE:NAME) or (*THEN:NAME).
|
names that are set by (*PRUNE:NAME) or (*THEN:NAME).
|
||||||
|
|
@ -3567,6 +3574,6 @@ Cambridge, England.
|
||||||
.rs
|
.rs
|
||||||
.sp
|
.sp
|
||||||
.nf
|
.nf
|
||||||
Last updated: 11 July 2018
|
Last updated: 16 July 2018
|
||||||
Copyright (c) 1997-2018 University of Cambridge.
|
Copyright (c) 1997-2018 University of Cambridge.
|
||||||
.fi
|
.fi
|
||||||
|
|
|
||||||
Loading…
Reference in New Issue