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3  <title>pcrecompat specification</title>  <title>pcrecompat specification</title>
4  </head>  </head>
5  <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">  <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6  This HTML document has been generated automatically from the original man page.  <h1>pcrecompat man page</h1>
7  If there is any nonsense in it, please consult the man page, in case the  <p>
8  conversion went wrong.<br>  Return to the <a href="index.html">PCRE index page</a>.
9  <ul>  </p>
10  <li><a name="TOC1" href="#SEC1">DIFFERENCES FROM PERL</a>  <p>
11  </ul>  This page is part of the PCRE HTML documentation. It was generated automatically
12  <br><a name="SEC1" href="#TOC1">DIFFERENCES FROM PERL</a><br>  from the original man page. If there is any nonsense in it, please consult the
13    man page, in case the conversion went wrong.
14    <br>
15    <br><b>
16    DIFFERENCES BETWEEN PCRE AND PERL
17    </b><br>
18  <P>  <P>
19  This document describes the differences in the ways that PCRE and Perl handle  This document describes the differences in the ways that PCRE and Perl handle
20  regular expressions. The differences described here are with respect to Perl  regular expressions. The differences described here are with respect to Perl
# Line 39  negative lookahead assertion contains ju Line 44  negative lookahead assertion contains ju
44  <P>  <P>
45  4. Though binary zero characters are supported in the subject string, they are  4. Though binary zero characters are supported in the subject string, they are
46  not allowed in a pattern string because it is passed as a normal C string,  not allowed in a pattern string because it is passed as a normal C string,
47  terminated by zero. The escape sequence "\0" can be used in the pattern to  terminated by zero. The escape sequence \0 can be used in the pattern to
48  represent a binary zero.  represent a binary zero.
49  </P>  </P>
50  <P>  <P>
51  5. The following Perl escape sequences are not supported: \l, \u, \L,  5. The following Perl escape sequences are not supported: \l, \u, \L,
52  \U, \P, \p, \N, and \X. In fact these are implemented by Perl's general  \U, and \N. In fact these are implemented by Perl's general string-handling
53  string-handling and are not part of its pattern matching engine. If any of  and are not part of its pattern matching engine. If any of these are
54  these are encountered by PCRE, an error is generated.  encountered by PCRE, an error is generated.
55    </P>
56    <P>
57    6. The Perl escape sequences \p, \P, and \X are supported only if PCRE is
58    built with Unicode character property support. The properties that can be
59    tested with \p and \P are limited to the general category properties such as
60    Lu and Nd.
61  </P>  </P>
62  <P>  <P>
63  6. PCRE does support the \Q...\E escape for quoting substrings. Characters in  7. PCRE does support the \Q...\E escape for quoting substrings. Characters in
64  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 $
65  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
66  variable interpolation (but of course PCRE does not have variables). Note the  variable interpolation (but of course PCRE does not have variables). Note the
67  following examples:  following examples:
 </P>  
 <P>  
68  <pre>  <pre>
69      Pattern            PCRE matches      Perl matches      Pattern            PCRE matches      Perl matches
70  </PRE>  
71  </P>      \Qabc$xyz\E        abc$xyz           abc followed by the contents of $xyz
 <P>  
 <pre>  
     \Qabc$xyz\E        abc$xyz           abc followed by the  
                                            contents of $xyz  
72      \Qabc\$xyz\E       abc\$xyz          abc\$xyz      \Qabc\$xyz\E       abc\$xyz          abc\$xyz
73      \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz      \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
74  </PRE>  </pre>
 </P>  
 <P>  
75  The \Q...\E sequence is recognized both inside and outside character classes.  The \Q...\E sequence is recognized both inside and outside character classes.
76  </P>  </P>
77  <P>  <P>
78  7. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})  8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})
79  constructions. However, there is some experimental support for recursive  constructions. However, there is support for recursive patterns using the
80  patterns using the non-Perl items (?R), (?number) and (?P&#62;name). Also, the PCRE  non-Perl items (?R), (?number), and (?P&#62;name). Also, the PCRE "callout" feature
81  "callout" feature allows an external function to be called during pattern  allows an external function to be called during pattern matching. See the
82  matching.  <a href="pcrecallout.html"><b>pcrecallout</b></a>
83    documentation for details.
84  </P>  </P>
85  <P>  <P>
86  8. There are some differences that are concerned with the settings of captured  9. There are some differences that are concerned with the settings of captured
87  strings when part of a pattern is repeated. For example, matching "aba" against  strings when part of a pattern is repeated. For example, matching "aba" against
88  the pattern /^(a(b)?)+$/ 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".
89  </P>  </P>
90  <P>  <P>
91  9. PCRE provides some extensions to the Perl regular expression facilities:  10. PCRE provides some extensions to the Perl regular expression facilities:
92  </P>  <br>
93  <P>  <br>
94  (a) Although lookbehind assertions must match fixed length strings, each  (a) Although lookbehind assertions must match fixed length strings, each
95  alternative branch of a lookbehind assertion can match a different length of  alternative branch of a lookbehind assertion can match a different length of
96  string. Perl requires them all to have the same length.  string. Perl requires them all to have the same length.
97  </P>  <br>
98  <P>  <br>
99  (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $  (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
100  meta-character matches only at the very end of the string.  meta-character matches only at the very end of the string.
101  </P>  <br>
102  <P>  <br>
103  &copy; If PCRE_EXTRA is set, a backslash followed by a letter with no special  (c) If PCRE_EXTRA is set, a backslash followed by a letter with no special
104  meaning is faulted.  meaning is faulted.
105  </P>  <br>
106  <P>  <br>
107  (d) If PCRE_UNGREEDY is set, the greediness of the repetition quantifiers is  (d) If PCRE_UNGREEDY is set, the greediness of the repetition quantifiers is
108  inverted, that is, by default they are not greedy, but if followed by a  inverted, that is, by default they are not greedy, but if followed by a
109  question mark they are.  question mark they are.
110  </P>  <br>
111  <P>  <br>
112  (e) PCRE_ANCHORED can be used to force a pattern to be tried only at the first  (e) PCRE_ANCHORED can be used at matching time to force a pattern to be tried
113  matching position in the subject string.  only at the first matching position in the subject string.
114  </P>  <br>
115  <P>  <br>
116  (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAPTURE  (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAPTURE
117  options for <b>pcre_exec()</b> have no Perl equivalents.  options for <b>pcre_exec()</b> have no Perl equivalents.
118  </P>  <br>
119  <P>  <br>
120  (g) The (?R), (?number), and (?P&#62;name) constructs allows for recursive pattern  (g) The (?R), (?number), and (?P&#62;name) constructs allows for recursive pattern
121  matching (Perl can do this using the (?p{code}) construct, which PCRE cannot  matching (Perl can do this using the (?p{code}) construct, which PCRE cannot
122  support.)  support.)
123  </P>  <br>
124  <P>  <br>
125  (h) PCRE supports named capturing substrings, using the Python syntax.  (h) PCRE supports named capturing substrings, using the Python syntax.
126  </P>  <br>
127  <P>  <br>
128  (i) PCRE supports the possessive quantifier "++" syntax, taken from Sun's Java  (i) PCRE supports the possessive quantifier "++" syntax, taken from Sun's Java
129  package.  package.
130  </P>  <br>
131  <P>  <br>
132  (j) The (R) condition, for testing recursion, is a PCRE extension.  (j) The (R) condition, for testing recursion, is a PCRE extension.
133  </P>  <br>
134  <P>  <br>
135  (k) The callout facility is PCRE-specific.  (k) The callout facility is PCRE-specific.
136    <br>
137    <br>
138    (l) The partial matching facility is PCRE-specific.
139    <br>
140    <br>
141    (m) Patterns compiled by PCRE can be saved and re-used at a later time, even on
142    different hosts that have the other endianness.
143  </P>  </P>
144  <P>  <P>
145  Last updated: 09 December 2003  Last updated: 09 September 2004
146  <br>  <br>
147  Copyright &copy; 1997-2003 University of Cambridge.  Copyright &copy; 1997-2004 University of Cambridge.
148    <p>
149    Return to the <a href="index.html">PCRE index page</a>.
150    </p>

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