/[pcre]/code/trunk/doc/pcrecompat.3
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revision 627 by ph10, Mon May 2 10:47:52 2011 UTC revision 628 by ph10, Wed Jul 20 18:03:20 2011 UTC
# Line 50  Perl documentation says "Because Perl hi Line 50  Perl documentation says "Because Perl hi
50  the internal representation of Unicode characters, there is no need to  the internal representation of Unicode characters, there is no need to
51  implement the somewhat messy concept of surrogates."  implement the somewhat messy concept of surrogates."
52  .P  .P
53  7. PCRE does support the \eQ...\eE escape for quoting substrings. Characters in  7. PCRE implements a simpler version of \eX than Perl, which changed to make
54    \eX match what Unicode calls an "extended grapheme cluster". This is more
55    complicated than an extended Unicode sequence, which is what PCRE matches.
56    .P
57    8. PCRE does support the \eQ...\eE escape for quoting substrings. Characters in
58  between are treated as literals. This is slightly different from Perl in that $  between are treated as literals. This is slightly different from Perl in that $
59  and @ are also handled as literals inside the quotes. In Perl, they cause  and @ are also handled as literals inside the quotes. In Perl, they cause
60  variable interpolation (but of course PCRE does not have variables). Note the  variable interpolation (but of course PCRE does not have variables). Note the
# Line 66  following examples: Line 70  following examples:
70  .sp  .sp
71  The \eQ...\eE sequence is recognized both inside and outside character classes.  The \eQ...\eE sequence is recognized both inside and outside character classes.
72  .P  .P
73  8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})  9. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
74  constructions. However, there is support for recursive patterns. This is not  constructions. However, there is support for recursive patterns. This is not
75  available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE "callout"  available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE "callout"
76  feature allows an external function to be called during pattern matching. See  feature allows an external function to be called during pattern matching. See
# Line 76  the Line 80  the
80  .\"  .\"
81  documentation for details.  documentation for details.
82  .P  .P
83  9. Subpatterns that are called recursively or as "subroutines" are always  10. Subpatterns that are called recursively or as "subroutines" are always
84  treated as atomic groups in PCRE. This is like Python, but unlike Perl. There  treated as atomic groups in PCRE. This is like Python, but unlike Perl. There
85  is a discussion of an example that explains this in more detail in the  is a discussion of an example that explains this in more detail in the
86  .\" HTML <a href="pcrepattern.html#recursiondifference">  .\" HTML <a href="pcrepattern.html#recursiondifference">
# Line 89  in the Line 93  in the
93  .\"  .\"
94  page.  page.
95  .P  .P
96  10. There are some differences that are concerned with the settings of captured  11. There are some differences that are concerned with the settings of captured
97  strings when part of a pattern is repeated. For example, matching "aba" against  strings when part of a pattern is repeated. For example, matching "aba" against
98  the pattern /^(a(b)?)+$/ in Perl leaves $2 unset, but in PCRE it is set to "b".  the pattern /^(a(b)?)+$/ in Perl leaves $2 unset, but in PCRE it is set to "b".
99  .P  .P
100  11. PCRE's handling of duplicate subpattern numbers and duplicate subpattern  12. PCRE's handling of duplicate subpattern numbers and duplicate subpattern
101  names is not as general as Perl's. This is a consequence of the fact the PCRE  names is not as general as Perl's. This is a consequence of the fact the PCRE
102  works internally just with numbers, using an external table to translate  works internally just with numbers, using an external table to translate
103  between numbers and names. In particular, a pattern such as (?|(?<a>A)|(?<b)B),  between numbers and names. In particular, a pattern such as (?|(?<a>A)|(?<b)B),
# Line 103  would not be possible to distinguish whi Line 107  would not be possible to distinguish whi
107  names map to capturing subpattern number 1. To avoid this confusing situation,  names map to capturing subpattern number 1. To avoid this confusing situation,
108  an error is given at compile time.  an error is given at compile time.
109  .P  .P
110  12. Perl recognizes comments in some places that PCRE doesn't, for example,  13. Perl recognizes comments in some places that PCRE doesn't, for example,
111  between the ( and ? at the start of a subpattern.  between the ( and ? at the start of a subpattern.
112  .P  .P
113  13. PCRE provides some extensions to the Perl regular expression facilities.  14. PCRE provides some extensions to the Perl regular expression facilities.
114  Perl 5.10 includes new features that are not in earlier versions of Perl, some  Perl 5.10 includes new features that are not in earlier versions of Perl, some
115  of which (such as named parentheses) have been in PCRE for some time. This list  of which (such as named parentheses) have been in PCRE for some time. This list
116  is with respect to Perl 5.10:  is with respect to Perl 5.10:
# Line 163  Cambridge CB2 3QH, England. Line 167  Cambridge CB2 3QH, England.
167  .rs  .rs
168  .sp  .sp
169  .nf  .nf
170  Last updated: 02 May 2011  Last updated: 20 July 2011
171  Copyright (c) 1997-2011 University of Cambridge.  Copyright (c) 1997-2011 University of Cambridge.
172  .fi  .fi

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