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Documentation update.

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Philip.Hazel 2018-07-16 16:09:34 +00:00
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31
doc/html/pcre2pattern.html
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@ -3176,14 +3176,23 @@ 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.
</P>
<P>
When a match succeeds, the name of the last-encountered (*MARK:NAME),
(*PRUNE:NAME), or (*THEN:NAME) on the matching path is passed back to the
caller as described in the section entitled
When a match succeeds, the name of the last-encountered (*MARK:NAME) on the
matching path is passed back to the caller as described in the section entitled
<a href="pcre2api.html#matchotherdata">"Other information about the match"</a>
in the
<a href="pcre2api.html"><b>pcre2api</b></a>
documentation. Here is an example of <b>pcre2test</b> output, where the "mark"
modifier requests the retrieval and outputting of (*MARK) data:
documentation. This applies to all instances of (*MARK), including those inside
assertions and atomic groups. (There are differences in those cases when
(*MARK) is used in conjunction with (*SKIP) as described below.)
</P>
<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>
<P>
Here is an example of <b>pcre2test</b> output, where the "mark" modifier
requests the retrieval and outputting of (*MARK) data:
<pre>
re&#62; /X(*MARK:A)Y|X(*MARK:B)Z/mark
data&#62; XY
@ -3344,14 +3353,14 @@ following <b>pcre2test</b> examples:
0: b
1: b
</pre>
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
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
allows (*SKIP:X) to immediately cause a new matching attempt to start at the
second character. This time, the (*MARK) is never seen because "a" does not
match "b", so the matcher immediately jumps to the second branch of the
pattern.
allows (*SKIP:X) to find the (*MARK) when it backtracks, and this causes a new
matching attempt to start at the second character. This time, the (*MARK) is
never seen because "a" does not match "b", so the matcher immediately jumps to
the second branch of the pattern.
</P>
<P>
Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It ignores
@ -3542,7 +3551,7 @@ Cambridge, England.
</P>
<br><a name="SEC30" href="#TOC1">REVISION</a><br>
<P>
Last updated: 11 July 2018
Last updated: 16 July 2018
<br>
Copyright &copy; 1997-2018 University of Cambridge.
<br>

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

31
doc/pcre2pattern.3
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@ -1,4 +1,4 @@
.TH PCRE2PATTERN 3 "11 July 2018" "PCRE2 10.32"
.TH PCRE2PATTERN 3 "16 July 2018" "PCRE2 10.32"
.SH NAME
PCRE2 - Perl-compatible regular expressions (revised API)
.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
(*MARK) as you like in a pattern, and their names do not have to be unique.
.P
When a match succeeds, the name of the last-encountered (*MARK:NAME),
(*PRUNE:NAME), or (*THEN:NAME) on the matching path is passed back to the
caller as described in the section entitled
When a match succeeds, the name of the last-encountered (*MARK:NAME) on the
matching path is passed back to the caller as described in the section entitled
.\" HTML <a href="pcre2api.html#matchotherdata">
.\" </a>
"Other information about the match"
@ -3217,8 +3216,16 @@ in the
.\" HREF
\fBpcre2api\fP
.\"
documentation. Here is an example of \fBpcre2test\fP output, where the "mark"
modifier requests the retrieval and outputting of (*MARK) data:
documentation. This applies to all instances of (*MARK), including those inside
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
re> /X(*MARK:A)Y|X(*MARK:B)Z/mark
data> XY
@ -3374,14 +3381,14 @@ following \fBpcre2test\fP examples:
0: b
1: b
.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
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
allows (*SKIP:X) to immediately cause a new matching attempt to start at the
second character. This time, the (*MARK) is never seen because "a" does not
match "b", so the matcher immediately jumps to the second branch of the
pattern.
allows (*SKIP:X) to find the (*MARK) when it backtracks, and this causes a new
matching attempt to start at the second character. This time, the (*MARK) is
never seen because "a" does not match "b", so the matcher immediately jumps to
the second branch of the pattern.
.P
Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It ignores
names that are set by (*PRUNE:NAME) or (*THEN:NAME).
@ -3567,6 +3574,6 @@ Cambridge, England.
.rs
.sp
.nf
Last updated: 11 July 2018
Last updated: 16 July 2018
Copyright (c) 1997-2018 University of Cambridge.
.fi