/[pcre]/code/trunk/doc/html/pcregrep.html

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-revision 566 by ph10,
Thu Jun  3 19:18:24 2010 UTC
+revision 567 by ph10,
Sat Nov  6 17:10:00 2010 UTC
 Line 366 
 locale is specified, the PCRE library's
  used. There is no short form for this option.
  </P>
  <P>
+ <b>--match-limit</b>=<i>number</i>
+ Processing some regular expression patterns can require a very large amount of
+ memory, leading in some cases to a program crash if not enough is available.
+ Other patterns may take a very long time to search for all possible matching
+ strings. The <b>pcre_exec()</b> function that is called by <b>pcregrep</b> to do
+ the matching has two parameters that can limit the resources that it uses.
+ <br>
+ <br>
+ The <b>--match-limit</b> option provides a means of limiting resource usage
+ when processing patterns that are not going to match, but which have a very
+ large number of possibilities in their search trees. The classic example is a
+ pattern that uses nested unlimited repeats. Internally, PCRE uses a function
+ called <b>match()</b> which it calls repeatedly (sometimes recursively). The
+ limit set by \fb--match-limit\fP is imposed on the number of times this
+ function is called during a match, which has the effect of limiting the amount
+ of backtracking that can take place.
+ <br>
+ <br>
+ The <b>--recursion-limit</b> option is similar to <b>--match-limit</b>, but
+ instead of limiting the total number of times that <b>match()</b> is called, it
+ limits the depth of recursive calls, which in turn limits the amount of memory
+ that can be used. The recursion depth is a smaller number than the total number
+ of calls, because not all calls to <b>match()</b> are recursive. This limit is
+ of use only if it is set smaller than <b>--match-limit</b>.
+ <br>
+ <br>
+ There are no short forms for these options. The default settings are specified
+ when the PCRE library is compiled, with the default default being 10 million.
+ </P>
+ <P>
  <b>-M</b>, <b>--multiline</b>
  Allow patterns to match more than one line. When this option is given, patterns
  may usefully contain literal newline characters and internal occurrences of ^
-Line 380 
 are guaranteed to be available for lookb
+Line 410 
 are guaranteed to be available for lookb
  work when input is read line by line (see \fP--line-buffered\fP.)
  </P>
  <P>
- <b>-N</b> <i>newline-type</i>, <b>--newline=</b><i>newline-type</i>
+ <b>-N</b> <i>newline-type</i>, <b>--newline</b>=<i>newline-type</i>
  The PCRE library supports five different conventions for indicating
  the ends of lines. They are the single-character sequences CR (carriage return)
  and LF (linefeed), the two-character sequence CRLF, an "anycrlf" convention,
-Line 409 
 output, it precedes the line number. Thi
+Line 439 
 output, it precedes the line number. Thi
  </P>
  <P>
  <b>-o</b>, <b>--only-matching</b>
- Show only the part of the line that matched a pattern. In this mode, no
+ Show only the part of the line that matched a pattern instead of the whole
- context is shown. That is, the <b>-A</b>, <b>-B</b>, and <b>-C</b> options are
+ line. In this mode, no context is shown. That is, the <b>-A</b>, <b>-B</b>, and
- ignored. If there is more than one match in a line, each of them is shown
+ <b>-C</b> options are ignored. If there is more than one match in a line, each
- separately. If <b>-o</b> is combined with <b>-v</b> (invert the sense of the
+ of them is shown separately. If <b>-o</b> is combined with <b>-v</b> (invert the
- match to find non-matching lines), no output is generated, but the return code
+ sense of the match to find non-matching lines), no output is generated, but the
- is set appropriately. This option is mutually exclusive with
+ return code is set appropriately. If the matched portion of the line is empty,
- <b>--file-offsets</b> and <b>--line-offsets</b>.
+ nothing is output unless the file name or line number are being printed, in
+ which case they are shown on an otherwise empty line. This option is mutually
+ exclusive with <b>--file-offsets</b> and <b>--line-offsets</b>.
+ </P>
+ <P>
+ <b>-o</b><i>number</i>, <b>--only-matching</b>=<i>number</i>
+ Show only the part of the line that matched the capturing parentheses of the
+ given number. Up to 32 capturing parentheses are supported. Because these
+ options can be given without an argument (see above), if an argument is
+ present, it must be given in the same shell item, for example, -o3 or
+ --only-matching=2. The comments given for the non-argument case above also
+ apply to this case. If the specified capturing parentheses do not exist in the
+ pattern, or were not set in the match, nothing is output unless the file name
+ or line number are being printed.
  </P>
  <P>
  <b>-q</b>, <b>--quiet</b>
-Line 431 
 immediate end-of-file. This option is a
+Line 474 
 immediate end-of-file. This option is a
  option to "recurse".
  </P>
  <P>
+ <b>--recursion-limit</b>=<i>number</i>
+ See <b>--match-limit</b> above.
+ </P>
+ <P>
  <b>-s</b>, <b>--no-messages</b>
  Suppress error messages about non-existent or unreadable files. Such files are
  quietly skipped. However, the return code is still 2, even if matches were
-Line 550 
 Cambridge CB2 3QH, England.
+Line 597 
 Cambridge CB2 3QH, England.
  </P>
  <br><a name="SEC13" href="#TOC1">REVISION</a><br>
  <P>
- Last updated: 21 May 2010
+ Last updated: 31 October 2010
  <br>
  Copyright &copy; 1997-2010 University of Cambridge.
  <br>

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