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<title>Perl Format String Syntax</title>
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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_regex.format.perl_format"></a><a class="link" href="perl_format.html" title="Perl Format String Syntax"> Perl Format String Syntax</a>
</h3></div></div></div>
<p>
Perl-style format strings treat all characters as literals except '$' and
'\' which start placeholder and escape sequences respectively.
</p>
<p>
Placeholder sequences specify that some part of what matched the regular
expression should be sent to output as follows:
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Placeholder
</p>
</th>
<th>
<p>
Meaning
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
$&
</p>
</td>
<td>
<p>
Outputs what matched the whole expression.
</p>
</td>
</tr>
<tr>
<td>
<p>
$MATCH
</p>
</td>
<td>
<p>
As $&
</p>
</td>
</tr>
<tr>
<td>
<p>
${^MATCH}
</p>
</td>
<td>
<p>
As $&
</p>
</td>
</tr>
<tr>
<td>
<p>
$`
</p>
</td>
<td>
<p>
Outputs the text between the end of the last match found (or the
start of the text if no previous match was found), and the start
of the current match.
</p>
</td>
</tr>
<tr>
<td>
<p>
$PREMATCH
</p>
</td>
<td>
<p>
As $`
</p>
</td>
</tr>
<tr>
<td>
<p>
${^PREMATCH}
</p>
</td>
<td>
<p>
As $`
</p>
</td>
</tr>
<tr>
<td>
<p>
$'
</p>
</td>
<td>
<p>
Outputs all the text following the end of the current match.
</p>
</td>
</tr>
<tr>
<td>
<p>
$POSTMATCH
</p>
</td>
<td>
<p>
As $'
</p>
</td>
</tr>
<tr>
<td>
<p>
${^POSTMATCH}
</p>
</td>
<td>
<p>
As $'
</p>
</td>
</tr>
<tr>
<td>
<p>
$+
</p>
</td>
<td>
<p>
Outputs what matched the last marked sub-expression in the regular
expression.
</p>
</td>
</tr>
<tr>
<td>
<p>
$LAST_PAREN_MATCH
</p>
</td>
<td>
<p>
As $+
</p>
</td>
</tr>
<tr>
<td>
<p>
$LAST_SUBMATCH_RESULT
</p>
</td>
<td>
<p>
Outputs what matched the last sub-expression to be actually matched.
</p>
</td>
</tr>
<tr>
<td>
<p>
$^N
</p>
</td>
<td>
<p>
As $LAST_SUBMATCH_RESULT
</p>
</td>
</tr>
<tr>
<td>
<p>
$$
</p>
</td>
<td>
<p>
Outputs a literal '$'
</p>
</td>
</tr>
<tr>
<td>
<p>
$n
</p>
</td>
<td>
<p>
Outputs what matched the n'th sub-expression.
</p>
</td>
</tr>
<tr>
<td>
<p>
${n}
</p>
</td>
<td>
<p>
Outputs what matched the n'th sub-expression.
</p>
</td>
</tr>
<tr>
<td>
<p>
$+{NAME}
</p>
</td>
<td>
<p>
Outputs whatever matched the sub-expression named "NAME".
</p>
</td>
</tr>
</tbody>
</table></div>
<p>
Any $-placeholder sequence not listed above, results in '$' being treated
as a literal.
</p>
<p>
An escape character followed by any character x, outputs that character unless
x is one of the escape sequences shown below.
</p>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Escape
</p>
</th>
<th>
<p>
Meaning
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
\a
</p>
</td>
<td>
<p>
Outputs the bell character: '\a'.
</p>
</td>
</tr>
<tr>
<td>
<p>
\e
</p>
</td>
<td>
<p>
Outputs the ANSI escape character (code point 27).
</p>
</td>
</tr>
<tr>
<td>
<p>
\f
</p>
</td>
<td>
<p>
Outputs a form feed character: '\f'
</p>
</td>
</tr>
<tr>
<td>
<p>
\n
</p>
</td>
<td>
<p>
Outputs a newline character: '\n'.
</p>
</td>
</tr>
<tr>
<td>
<p>
\r
</p>
</td>
<td>
<p>
Outputs a carriage return character: '\r'.
</p>
</td>
</tr>
<tr>
<td>
<p>
\t
</p>
</td>
<td>
<p>
Outputs a tab character: '\t'.
</p>
</td>
</tr>
<tr>
<td>
<p>
\v
</p>
</td>
<td>
<p>
Outputs a vertical tab character: '\v'.
</p>
</td>
</tr>
<tr>
<td>
<p>
\xDD
</p>
</td>
<td>
<p>
Outputs the character whose hexadecimal code point is 0xDD
</p>
</td>
</tr>
<tr>
<td>
<p>
\x{DDDD}
</p>
</td>
<td>
<p>
Outputs the character whose hexadecimal code point is 0xDDDDD
</p>
</td>
</tr>
<tr>
<td>
<p>
\cX
</p>
</td>
<td>
<p>
Outputs the ANSI escape sequence "escape-X".
</p>
</td>
</tr>
<tr>
<td>
<p>
\D
</p>
</td>
<td>
<p>
If D is a decimal digit in the range 1-9, then outputs the text
that matched sub-expression D.
</p>
</td>
</tr>
<tr>
<td>
<p>
\l
</p>
</td>
<td>
<p>
Causes the next character to be outputted, to be output in lower
case.
</p>
</td>
</tr>
<tr>
<td>
<p>
\u
</p>
</td>
<td>
<p>
Causes the next character to be outputted, to be output in upper
case.
</p>
</td>
</tr>
<tr>
<td>
<p>
\L
</p>
</td>
<td>
<p>
Causes all subsequent characters to be output in lower case, until
a \E is found.
</p>
</td>
</tr>
<tr>
<td>
<p>
\U
</p>
</td>
<td>
<p>
Causes all subsequent characters to be output in upper case, until
a \E is found.
</p>
</td>
</tr>
<tr>
<td>
<p>
\E
</p>
</td>
<td>
<p>
Terminates a \L or \U sequence.
</p>
</td>
</tr>
</tbody>
</table></div>
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<td align="right"><div class="copyright-footer">Copyright © 1998 -2007 John Maddock<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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