Documentation update.
This commit is contained in:
Philip.Hazel
parent
b196143523
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c722bf2399
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@ -1813,41 +1813,68 @@ duplicate named subpatterns, as described in the next section.
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<br><a name="SEC16" href="#TOC1">NAMED SUBPATTERNS</a><br>
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<P>
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Identifying capturing parentheses by number is simple, but it can be very hard
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to keep track of the numbers in complicated regular expressions. Furthermore,
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if an expression is modified, the numbers may change. To help with this
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difficulty, PCRE2 supports the naming of subpatterns. This feature was not
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added to Perl until release 5.10. Python had the feature earlier, and PCRE1
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to keep track of the numbers in complicated patterns. Furthermore, if an
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expression is modified, the numbers may change. To help with this difficulty,
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PCRE2 supports the naming of capturing subpatterns. This feature was not added
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to Perl until release 5.10. Python had the feature earlier, and PCRE1
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introduced it at release 4.0, using the Python syntax. PCRE2 supports both the
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Perl and the Python syntax. Perl allows identically numbered subpatterns to
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have different names, but PCRE2 does not.
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Perl and the Python syntax.
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</P>
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<P>
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In PCRE2, a subpattern can be named in one of three ways: (?<name>...) or
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(?'name'...) as in Perl, or (?P<name>...) as in Python. References to capturing
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parentheses from other parts of the pattern, such as
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In PCRE2, a capturing subpattern can be named in one of three ways:
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(?<name>...) or (?'name'...) as in Perl, or (?P<name>...) as in Python. Names
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consist of up to 32 alphanumeric characters and underscores, but must start
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with a non-digit. References to capturing parentheses from other parts of the
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pattern, such as
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<a href="#backreferences">backreferences,</a>
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<a href="#recursion">recursion,</a>
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and
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<a href="#conditions">conditions,</a>
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can be made by name as well as by number.
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can all be made by name as well as by number.
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</P>
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<P>
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Names consist of up to 32 alphanumeric characters and underscores, but must
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start with a non-digit. Named capturing parentheses are still allocated numbers
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as well as names, exactly as if the names were not present. The PCRE2 API
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provides function calls for extracting the name-to-number translation table
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from a compiled pattern. There are also convenience functions for extracting a
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captured substring by name.
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Named capturing parentheses are allocated numbers as well as names, exactly as
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if the names were not present. In both PCRE2 and Perl, capturing subpatterns
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are primarily identified by numbers; any names are just aliases for these
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numbers. The PCRE2 API provides function calls for extracting the complete
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name-to-number translation table from a compiled pattern, as well as
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convenience functions for extracting captured substrings by name.
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</P>
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<P>
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By default, a name must be unique within a pattern, but it is possible to relax
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this constraint by setting the PCRE2_DUPNAMES option at compile time.
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(Duplicate names are also always permitted for subpatterns with the same
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number, set up as described in the previous section.) Duplicate names can be
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useful for patterns where only one instance of the named parentheses can match.
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Suppose you want to match the name of a weekday, either as a 3-letter
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abbreviation or as the full name, and in both cases you want to extract the
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abbreviation. This pattern (ignoring the line breaks) does the job:
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<b>Warning:</b> When more than one subpattern has the same number, as described
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in the previous section, a name given to one of them applies to all of them.
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Perl allows identically numbered subpatterns to have different names. Consider
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this pattern, where there are two capturing subpatterns, both numbered 1:
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<pre>
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(?|(?<AA>aa)|(?<BB>bb))
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</pre>
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Perl allows this, with both names AA and BB as aliases of group 1. Thus, after
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a successful match, both names yield the same value (either "aa" or "bb").
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</P>
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<P>
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In an attempt to reduce confusion, PCRE2 does not allow the same group number
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to be associated with more than one name. The example above provokes a
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compile-time error. However, there is still scope for confusion. Consider this
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pattern:
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<pre>
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(?|(?<AA>aa)|(bb))
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</pre>
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Although the second subpattern number 1 is not explicitly named, the name AA is
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still an alias for subpattern 1. Whether the pattern matches "aa" or "bb", a
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reference by name to group AA yields the matched string.
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</P>
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<P>
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By default, a name must be unique within a pattern, except that duplicate names
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are permitted for subpatterns with the same number, for example:
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<pre>
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(?|(?<AA>aa)|(?<AA>bb))
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</pre>
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The duplicate name constraint can be disabled by setting the PCRE2_DUPNAMES
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option at compile time, or by the use of (?J) within the pattern. Duplicate
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names can be useful for patterns where only one instance of the named
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parentheses can match. Suppose you want to match the name of a weekday, either
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as a 3-letter abbreviation or as the full name, and in both cases you want to
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extract the abbreviation. This pattern (ignoring the line breaks) does the job:
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<pre>
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(?<DN>Mon|Fri|Sun)(?:day)?|
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(?<DN>Tue)(?:sday)?|
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@ -1856,13 +1883,11 @@ abbreviation. This pattern (ignoring the line breaks) does the job:
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(?<DN>Sat)(?:urday)?
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</pre>
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There are five capturing substrings, but only one is ever set after a match.
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(An alternative way of solving this problem is to use a "branch reset"
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subpattern, as described in the previous section.)
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</P>
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<P>
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The convenience functions for extracting the data by name returns the substring
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for the first (and in this example, the only) subpattern of that name that
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matched. This saves searching to find which numbered subpattern it was.
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matched. This saves searching to find which numbered subpattern it was. (An
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alternative way of solving this problem is to use a "branch reset" subpattern,
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as described in the previous section.)
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</P>
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<P>
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If you make a backreference to a non-unique named subpattern from elsewhere in
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@ -1878,8 +1903,7 @@ for the reference. For example, this pattern matches both "foofoo" and
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<P>
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If you make a subroutine call to a non-unique named subpattern, the one that
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corresponds to the first occurrence of the name is used. In the absence of
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duplicate numbers (see the previous section) this is the one with the lowest
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number.
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duplicate numbers this is the one with the lowest number.
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</P>
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<P>
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If you use a named reference in a condition
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@ -1893,14 +1917,6 @@ handling named subpatterns, see the
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<a href="pcre2api.html"><b>pcre2api</b></a>
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documentation.
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</P>
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<P>
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<b>Warning:</b> You cannot use different names to distinguish between two
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subpatterns with the same number because PCRE2 uses only the numbers when
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matching. For this reason, an error is given at compile time if different names
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are given to subpatterns with the same number. However, you can always give the
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same name to subpatterns with the same number, even when PCRE2_DUPNAMES is not
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set.
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</P>
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<br><a name="SEC17" href="#TOC1">REPETITION</a><br>
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<P>
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Repetition is specified by quantifiers, which can follow any of the following
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@ -2957,10 +2973,12 @@ later versions (I tried 5.024) it now works.
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<br><a name="SEC24" href="#TOC1">SUBPATTERNS AS SUBROUTINES</a><br>
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<P>
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If the syntax for a recursive subpattern call (either by number or by
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name) is used outside the parentheses to which it refers, it operates like a
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subroutine in a programming language. The called subpattern may be defined
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before or after the reference. A numbered reference can be absolute or
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relative, as in these examples:
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name) is used outside the parentheses to which it refers, it operates a bit
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like a subroutine in a programming language. More accurately, PCRE2 treats the
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referenced subpattern as an independent subpattern which it tries to match at
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the current matching position. The called subpattern may be defined before or
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after the reference. A numbered reference can be absolute or relative, as in
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these examples:
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<pre>
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(...(absolute)...)...(?2)...
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(...(relative)...)...(?-1)...
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@ -2993,6 +3011,13 @@ different calls. For example, consider this pattern:
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</pre>
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It matches "abcabc". It does not match "abcABC" because the change of
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processing option does not affect the called subpattern.
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</P>
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<P>
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The behaviour of
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<a href="#backtrackcontrol">backtracking control verbs</a>
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in subpatterns when called as subroutines is described in the section entitled
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<a href="#btsub">"Backtracking verbs in subroutines"</a>
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below.
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<a name="onigurumasubroutines"></a></P>
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<br><a name="SEC25" href="#TOC1">ONIGURUMA SUBROUTINE SYNTAX</a><br>
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<P>
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|
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107
doc/pcre2.txt
107
doc/pcre2.txt
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@ -7393,32 +7393,60 @@ DUPLICATE SUBPATTERN NUMBERS
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NAMED SUBPATTERNS
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Identifying capturing parentheses by number is simple, but it can be
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very hard to keep track of the numbers in complicated regular expres-
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sions. Furthermore, if an expression is modified, the numbers may
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change. To help with this difficulty, PCRE2 supports the naming of sub-
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patterns. This feature was not added to Perl until release 5.10. Python
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very hard to keep track of the numbers in complicated patterns. Fur-
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thermore, if an expression is modified, the numbers may change. To help
|
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with this difficulty, PCRE2 supports the naming of capturing subpat-
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terns. This feature was not added to Perl until release 5.10. Python
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had the feature earlier, and PCRE1 introduced it at release 4.0, using
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the Python syntax. PCRE2 supports both the Perl and the Python syntax.
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Perl allows identically numbered subpatterns to have different names,
|
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but PCRE2 does not.
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In PCRE2, a subpattern can be named in one of three ways: (?<name>...)
|
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or (?'name'...) as in Perl, or (?P<name>...) as in Python. References
|
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to capturing parentheses from other parts of the pattern, such as back-
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references, recursion, and conditions, can be made by name as well as
|
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by number.
|
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|
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In PCRE2, a capturing subpattern can be named in one of three ways:
|
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(?<name>...) or (?'name'...) as in Perl, or (?P<name>...) as in Python.
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Names consist of up to 32 alphanumeric characters and underscores, but
|
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must start with a non-digit. Named capturing parentheses are still
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allocated numbers as well as names, exactly as if the names were not
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present. The PCRE2 API provides function calls for extracting the name-
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to-number translation table from a compiled pattern. There are also
|
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convenience functions for extracting a captured substring by name.
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must start with a non-digit. References to capturing parentheses from
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other parts of the pattern, such as backreferences, recursion, and con-
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ditions, can all be made by name as well as by number.
|
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By default, a name must be unique within a pattern, but it is possible
|
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to relax this constraint by setting the PCRE2_DUPNAMES option at com-
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pile time. (Duplicate names are also always permitted for subpatterns
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with the same number, set up as described in the previous section.)
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Named capturing parentheses are allocated numbers as well as names,
|
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exactly as if the names were not present. In both PCRE2 and Perl, cap-
|
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turing subpatterns are primarily identified by numbers; any names are
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just aliases for these numbers. The PCRE2 API provides function calls
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for extracting the complete name-to-number translation table from a
|
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compiled pattern, as well as convenience functions for extracting cap-
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tured substrings by name.
|
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Warning: When more than one subpattern has the same number, as
|
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described in the previous section, a name given to one of them applies
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to all of them. Perl allows identically numbered subpatterns to have
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different names. Consider this pattern, where there are two capturing
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subpatterns, both numbered 1:
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(?|(?<AA>aa)|(?<BB>bb))
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Perl allows this, with both names AA and BB as aliases of group 1.
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Thus, after a successful match, both names yield the same value (either
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"aa" or "bb").
|
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In an attempt to reduce confusion, PCRE2 does not allow the same group
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number to be associated with more than one name. The example above pro-
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vokes a compile-time error. However, there is still scope for confu-
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sion. Consider this pattern:
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(?|(?<AA>aa)|(bb))
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Although the second subpattern number 1 is not explicitly named, the
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name AA is still an alias for subpattern 1. Whether the pattern matches
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"aa" or "bb", a reference by name to group AA yields the matched
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string.
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By default, a name must be unique within a pattern, except that dupli-
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cate names are permitted for subpatterns with the same number, for
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example:
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(?|(?<AA>aa)|(?<AA>bb))
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The duplicate name constraint can be disabled by setting the PCRE2_DUP-
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NAMES option at compile time, or by the use of (?J) within the pattern.
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Duplicate names can be useful for patterns where only one instance of
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the named parentheses can match. Suppose you want to match the name of
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a weekday, either as a 3-letter abbreviation or as the full name, and
|
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|
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@ -7432,13 +7460,12 @@ NAMED SUBPATTERNS
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(?<DN>Sat)(?:urday)?
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There are five capturing substrings, but only one is ever set after a
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match. (An alternative way of solving this problem is to use a "branch
|
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reset" subpattern, as described in the previous section.)
|
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|
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The convenience functions for extracting the data by name returns the
|
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substring for the first (and in this example, the only) subpattern of
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that name that matched. This saves searching to find which numbered
|
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subpattern it was.
|
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match. The convenience functions for extracting the data by name
|
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returns the substring for the first (and in this example, the only)
|
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subpattern of that name that matched. This saves searching to find
|
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which numbered subpattern it was. (An alternative way of solving this
|
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problem is to use a "branch reset" subpattern, as described in the pre-
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vious section.)
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If you make a backreference to a non-unique named subpattern from else-
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where in the pattern, the subpatterns to which the name refers are
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@ -7451,8 +7478,7 @@ NAMED SUBPATTERNS
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If you make a subroutine call to a non-unique named subpattern, the one
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that corresponds to the first occurrence of the name is used. In the
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absence of duplicate numbers (see the previous section) this is the one
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with the lowest number.
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absence of duplicate numbers this is the one with the lowest number.
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If you use a named reference in a condition test (see the section about
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conditions below), either to check whether a subpattern has matched, or
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@ -7462,13 +7488,6 @@ NAMED SUBPATTERNS
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details of the interfaces for handling named subpatterns, see the
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pcre2api documentation.
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Warning: You cannot use different names to distinguish between two sub-
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patterns with the same number because PCRE2 uses only the numbers when
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matching. For this reason, an error is given at compile time if differ-
|
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ent names are given to subpatterns with the same number. However, you
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can always give the same name to subpatterns with the same number, even
|
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when PCRE2_DUPNAMES is not set.
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REPETITION
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@ -8472,10 +8491,12 @@ RECURSIVE PATTERNS
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SUBPATTERNS AS SUBROUTINES
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If the syntax for a recursive subpattern call (either by number or by
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name) is used outside the parentheses to which it refers, it operates
|
||||
like a subroutine in a programming language. The called subpattern may
|
||||
be defined before or after the reference. A numbered reference can be
|
||||
absolute or relative, as in these examples:
|
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name) is used outside the parentheses to which it refers, it operates a
|
||||
bit like a subroutine in a programming language. More accurately, PCRE2
|
||||
treats the referenced subpattern as an independent subpattern which it
|
||||
tries to match at the current matching position. The called subpattern
|
||||
may be defined before or after the reference. A numbered reference can
|
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be absolute or relative, as in these examples:
|
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|
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(...(absolute)...)...(?2)...
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(...(relative)...)...(?-1)...
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@ -8508,6 +8529,10 @@ SUBPATTERNS AS SUBROUTINES
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It matches "abcabc". It does not match "abcABC" because the change of
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processing option does not affect the called subpattern.
|
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|
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The behaviour of backtracking control verbs in subpatterns when called
|
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as subroutines is described in the section entitled "Backtracking verbs
|
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in subroutines" below.
|
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ONIGURUMA SUBROUTINE SYNTAX
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|
|
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@ -1815,17 +1815,18 @@ duplicate named subpatterns, as described in the next section.
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.rs
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.sp
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Identifying capturing parentheses by number is simple, but it can be very hard
|
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to keep track of the numbers in complicated regular expressions. Furthermore,
|
||||
if an expression is modified, the numbers may change. To help with this
|
||||
difficulty, PCRE2 supports the naming of subpatterns. This feature was not
|
||||
added to Perl until release 5.10. Python had the feature earlier, and PCRE1
|
||||
to keep track of the numbers in complicated patterns. Furthermore, if an
|
||||
expression is modified, the numbers may change. To help with this difficulty,
|
||||
PCRE2 supports the naming of capturing subpatterns. This feature was not added
|
||||
to Perl until release 5.10. Python had the feature earlier, and PCRE1
|
||||
introduced it at release 4.0, using the Python syntax. PCRE2 supports both the
|
||||
Perl and the Python syntax. Perl allows identically numbered subpatterns to
|
||||
have different names, but PCRE2 does not.
|
||||
Perl and the Python syntax.
|
||||
.P
|
||||
In PCRE2, 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
|
||||
In PCRE2, a capturing subpattern can be named in one of three ways:
|
||||
(?<name>...) or (?'name'...) as in Perl, or (?P<name>...) as in Python. Names
|
||||
consist of up to 32 alphanumeric characters and underscores, but must start
|
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with a non-digit. References to capturing parentheses from other parts of the
|
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pattern, such as
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.\" HTML <a href="#backreferences">
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.\" </a>
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backreferences,
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@ -1839,23 +1840,47 @@ and
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.\" </a>
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conditions,
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.\"
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can be made by name as well as by number.
|
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can all be made by name as well as by number.
|
||||
.P
|
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Names consist of up to 32 alphanumeric characters and underscores, but must
|
||||
start with a non-digit. Named capturing parentheses are still allocated numbers
|
||||
as well as names, exactly as if the names were not present. The PCRE2 API
|
||||
provides function calls for extracting the name-to-number translation table
|
||||
from a compiled pattern. There are also convenience functions for extracting a
|
||||
captured substring by name.
|
||||
Named capturing parentheses are allocated numbers as well as names, exactly as
|
||||
if the names were not present. In both PCRE2 and Perl, capturing subpatterns
|
||||
are primarily identified by numbers; any names are just aliases for these
|
||||
numbers. The PCRE2 API provides function calls for extracting the complete
|
||||
name-to-number translation table from a compiled pattern, as well as
|
||||
convenience functions for extracting captured substrings by name.
|
||||
.P
|
||||
By default, a name must be unique within a pattern, but it is possible to relax
|
||||
this constraint by setting the PCRE2_DUPNAMES option at compile time.
|
||||
(Duplicate names are also always permitted for subpatterns with the same
|
||||
number, set up as described in the previous section.) Duplicate names can be
|
||||
useful for patterns where only one instance of the named parentheses can match.
|
||||
Suppose you want to match the name of a weekday, either as a 3-letter
|
||||
abbreviation or as the full name, and in both cases you want to extract the
|
||||
abbreviation. This pattern (ignoring the line breaks) does the job:
|
||||
\fBWarning:\fP When more than one subpattern has the same number, as described
|
||||
in the previous section, a name given to one of them applies to all of them.
|
||||
Perl allows identically numbered subpatterns to have different names. Consider
|
||||
this pattern, where there are two capturing subpatterns, both numbered 1:
|
||||
.sp
|
||||
(?|(?<AA>aa)|(?<BB>bb))
|
||||
.sp
|
||||
Perl allows this, with both names AA and BB as aliases of group 1. Thus, after
|
||||
a successful match, both names yield the same value (either "aa" or "bb").
|
||||
.P
|
||||
In an attempt to reduce confusion, PCRE2 does not allow the same group number
|
||||
to be associated with more than one name. The example above provokes a
|
||||
compile-time error. However, there is still scope for confusion. Consider this
|
||||
pattern:
|
||||
.sp
|
||||
(?|(?<AA>aa)|(bb))
|
||||
.sp
|
||||
Although the second subpattern number 1 is not explicitly named, the name AA is
|
||||
still an alias for subpattern 1. Whether the pattern matches "aa" or "bb", a
|
||||
reference by name to group AA yields the matched string.
|
||||
.P
|
||||
By default, a name must be unique within a pattern, except that duplicate names
|
||||
are permitted for subpatterns with the same number, for example:
|
||||
.sp
|
||||
(?|(?<AA>aa)|(?<AA>bb))
|
||||
.sp
|
||||
The duplicate name constraint can be disabled by setting the PCRE2_DUPNAMES
|
||||
option at compile time, or by the use of (?J) within the pattern. Duplicate
|
||||
names can be useful for patterns where only one instance of the named
|
||||
parentheses can match. Suppose you want to match the name of a weekday, either
|
||||
as a 3-letter abbreviation or as the full name, and in both cases you want to
|
||||
extract the abbreviation. This pattern (ignoring the line breaks) does the job:
|
||||
.sp
|
||||
(?<DN>Mon|Fri|Sun)(?:day)?|
|
||||
(?<DN>Tue)(?:sday)?|
|
||||
|
|
@ -1864,12 +1889,11 @@ abbreviation. This pattern (ignoring the line breaks) does the job:
|
|||
(?<DN>Sat)(?:urday)?
|
||||
.sp
|
||||
There are five capturing substrings, but only one is ever set after a match.
|
||||
(An alternative way of solving this problem is to use a "branch reset"
|
||||
subpattern, as described in the previous section.)
|
||||
.P
|
||||
The convenience functions for extracting the data by name 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.
|
||||
matched. This saves searching to find which numbered subpattern it was. (An
|
||||
alternative way of solving this problem is to use a "branch reset" subpattern,
|
||||
as described in the previous section.)
|
||||
.P
|
||||
If you make a backreference to a non-unique named subpattern from elsewhere in
|
||||
the pattern, the subpatterns to which the name refers are checked in the order
|
||||
|
|
@ -1882,8 +1906,7 @@ for the reference. For example, this pattern matches both "foofoo" and
|
|||
.P
|
||||
If you make a subroutine call to a non-unique named subpattern, the one that
|
||||
corresponds to the first occurrence of the name is used. In the absence of
|
||||
duplicate numbers (see the previous section) this is the one with the lowest
|
||||
number.
|
||||
duplicate numbers this is the one with the lowest number.
|
||||
.P
|
||||
If you use a named reference in a condition
|
||||
test (see the
|
||||
|
|
@ -1901,13 +1924,6 @@ handling named subpatterns, see the
|
|||
\fBpcre2api\fP
|
||||
.\"
|
||||
documentation.
|
||||
.P
|
||||
\fBWarning:\fP You cannot use different names to distinguish between two
|
||||
subpatterns with the same number because PCRE2 uses only the numbers when
|
||||
matching. For this reason, an error is given at compile time if different names
|
||||
are given to subpatterns with the same number. However, you can always give the
|
||||
same name to subpatterns with the same number, even when PCRE2_DUPNAMES is not
|
||||
set.
|
||||
.
|
||||
.
|
||||
.SH REPETITION
|
||||
|
|
@ -2982,10 +2998,12 @@ later versions (I tried 5.024) it now works.
|
|||
.rs
|
||||
.sp
|
||||
If the syntax for a recursive subpattern call (either by number or by
|
||||
name) is used outside the parentheses to which it refers, it operates like a
|
||||
subroutine in a programming language. The called subpattern may be defined
|
||||
before or after the reference. A numbered reference can be absolute or
|
||||
relative, as in these examples:
|
||||
name) is used outside the parentheses to which it refers, it operates a bit
|
||||
like a subroutine in a programming language. More accurately, PCRE2 treats the
|
||||
referenced subpattern as an independent subpattern which it tries to match at
|
||||
the current matching position. The called subpattern may be defined before or
|
||||
after the reference. A numbered reference can be absolute or relative, as in
|
||||
these examples:
|
||||
.sp
|
||||
(...(absolute)...)...(?2)...
|
||||
(...(relative)...)...(?-1)...
|
||||
|
|
@ -3016,6 +3034,18 @@ different calls. For example, consider this pattern:
|
|||
.sp
|
||||
It matches "abcabc". It does not match "abcABC" because the change of
|
||||
processing option does not affect the called subpattern.
|
||||
.P
|
||||
The behaviour of
|
||||
.\" HTML <a href="#backtrackcontrol">
|
||||
.\" </a>
|
||||
backtracking control verbs
|
||||
.\"
|
||||
in subpatterns when called as subroutines is described in the section entitled
|
||||
.\" HTML <a href="#btsub">
|
||||
.\" </a>
|
||||
"Backtracking verbs in subroutines"
|
||||
.\"
|
||||
below.
|
||||
.
|
||||
.
|
||||
.\" HTML <a name="onigurumasubroutines"></a>
|
||||
|
|
|
|||
Loading…
Reference in New Issue