forked from boostorg/regex
218 lines
9.6 KiB
HTML
218 lines
9.6 KiB
HTML
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<title>Boost.Regex: Format String Syntax</title>
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<P>
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<TABLE id="Table1" cellSpacing="1" cellPadding="1" width="100%" border="0">
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<TR>
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<td valign="top" width="300">
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<h3><a href="../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../c++boost.gif" border="0"></a></h3>
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</td>
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<TD width="353">
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<H1 align="center">Boost.Regex</H1>
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<H2 align="center">Format String Syntax</H2>
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</TD>
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<td width="50">
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<h3><a href="index.html"><img height="45" width="43" alt="Boost.Regex Index" src="uarrow.gif" border="0"></a></h3>
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</td>
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</TR>
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</TABLE>
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</P>
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<HR>
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<p></p>
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<P>Format strings are used by the algorithm <A href="template_class_ref.htm#reg_merge">
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regex_merge</A> and by <A href="match_results.html">match_results::format</A>,
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and are used to transform one string into another.
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</P>
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<P>There are three kind of format string: sed, perl and extended, the extended
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syntax is a superset of the others so this is covered first.
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</P>
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<P><B><I>Extended format syntax</I></B>
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</P>
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<P>In format strings, all characters are treated as literals except: ()$\?:
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</P>
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<P>To use any of these as literals you must prefix them with the escape character
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\
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</P>
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<P>The following special sequences are recognized: <BR>
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<BR>
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<I>Grouping:</I>
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</P>
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<P>Use the parenthesis characters ( and ) to group sub-expressions within the
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format string, use \( and \) to represent literal '(' and ')'. <BR>
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<BR>
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<I>Sub-expression expansions:</I>
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</P>
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<P>The following perl like expressions expand to a particular matched
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sub-expression:
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<BR>
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</P>
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<P>
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<TABLE id="Table2" cellSpacing="0" cellPadding="7" width="100%" border="0">
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">$`</TD>
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<TD vAlign="top" width="43%">Expands to all the text from the end of the previous
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match to the start of the current match, if there was no previous match in the
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current operation, then everything from the start of the input string to the
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start of the match.</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">$'</TD>
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<TD vAlign="top" width="43%">Expands to all the text from the end of the match to
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the end of the input string.</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">$&</TD>
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<TD vAlign="top" width="43%">Expands to all of the current match.</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">$0</TD>
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<TD vAlign="top" width="43%">Expands to all of the current match.</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">$N</TD>
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<TD vAlign="top" width="43%">Expands to the text that matched sub-expression <I>N</I>.</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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</TABLE>
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</P>
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<P><I>Conditional expressions:</I>
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</P>
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<P>Conditional expressions allow two different format strings to be selected
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dependent upon whether a sub-expression participated in the match or not:
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</P>
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<P>?Ntrue_expression:false_expression
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</P>
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<P>Executes true_expression if sub-expression <I>N</I> participated in the match,
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otherwise executes false_expression.
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</P>
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<P>Example: suppose we search for "(while)|(for)" then the format string
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"?1WHILE:FOR" would output what matched, but in upper case. <BR>
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<BR>
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<I>Escape sequences:</I>
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</P>
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<P>The following escape sequences are also allowed:
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<BR>
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</P>
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<P>
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<TABLE id="Table3" cellSpacing="0" cellPadding="7" width="100%" border="0">
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">\a</TD>
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<TD vAlign="top" width="43%">The bell character.</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">\f</TD>
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<TD vAlign="top" width="43%">The form feed character.</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">\n</TD>
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<TD vAlign="top" width="43%">The newline character.</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">\r</TD>
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<TD vAlign="top" width="43%">The carriage return character.</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">\t</TD>
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<TD vAlign="top" width="43%">The tab character.</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">\v</TD>
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<TD vAlign="top" width="43%">A vertical tab character.</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">\x</TD>
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<TD vAlign="top" width="43%">A hexadecimal character - for example \x0D.</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">\x{}</TD>
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<TD vAlign="top" width="43%">A possible unicode hexadecimal character - for
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example \x{1A0}</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">\cx</TD>
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<TD vAlign="top" width="43%">The ASCII escape character x, for example \c@ is
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equivalent to escape-@.</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">\e</TD>
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<TD vAlign="top" width="43%">The ASCII escape character.</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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<TR>
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<TD vAlign="top" width="8%"> </TD>
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<TD vAlign="top" width="40%">\dd</TD>
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<TD vAlign="top" width="43%">An octal character constant, for example \10.</TD>
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<TD vAlign="top" width="9%"> </TD>
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</TR>
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</TABLE>
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</P>
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<P><B><I>Perl format strings</I></B>
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</P>
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<P>Perl format strings are the same as the default syntax except that the
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characters ()?: have no special meaning.
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</P>
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<P><B><I>Sed format strings</I></B>
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</P>
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<P>Sed format strings use only the characters \ and & as special characters.
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</P>
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<P>\n where n is a digit, is expanded to the nth sub-expression.
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</P>
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<P>& is expanded to the whole of the match (equivalent to \0).
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</P>
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<P>
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Other escape sequences are expanded as per the default syntax.
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<P>
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<HR>
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<P></P>
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<p>Revised
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<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
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11 April 2003
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<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
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</p>
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<P><I>© Copyright <a href="mailto:jm@regex.fsnet.co.uk">John Maddock</a> 1998-<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%Y" startspan --> 2003<!--webbot bot="Timestamp" endspan i-checksum="39359" --></I></P>
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<P align="left"><I>Permission to use, copy, modify, distribute and sell this software
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and its documentation for any purpose is hereby granted without fee, provided
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that the above copyright notice appear in all copies and that both that
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copyright notice and this permission notice appear in supporting documentation.
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Dr John Maddock makes no representations about the suitability of this software
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for any purpose. It is provided "as is" without express or implied warranty.</I></P>
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</body>
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</html>
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