/jEdit/tags/jedit-4-3-pre5/doc/users-guide/regexps.xml

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<appendix id="regexps"><title>Regular Expressions</title>
 <para>
  jEdit 4.3pre5 and later uses regular expressions from <ulink url="http://java.sun.com/j2se/1.4.2/docs/api/java/util/regex/Pattern.html">java.util.regex.Pattern</ulink>
  to implement inexact search and replace. Click there to see a complete reference guide to all supported meta-characters. </para>
  
  <para>
    A regular expression consists of a string where some characters are given special meaning with regard to pattern matching.
 </para>

 <note><title> Inside XML files </title>
  <para> Inside XML files (such as Jedit mode files), it is important that you escape XML special characters, such as &amp;, &lt;, &gt;, etc. You can use the XML plugin's "characters to entities" to perform this mapping.  </para>
  </note>

  <note> <title> Inside Java / beanshell / properties files </title>
  <para> Java strings are always parsed by java before they are processed by the regular expression engine, so you must make sure that backslashes are escaped by an extra backslash (<literal>\\</literal>)</para> </note>
  
 
 <para>
  Within a regular expression, the following characters have special meaning:
 </para>
 <bridgehead renderas="sect3">Positional Operators</bridgehead>
 <itemizedlist>
  <listitem><para><literal>^</literal> matches at the beginning of a line</para></listitem>
  <listitem><para><literal>$</literal> matches at the end of a line</para></listitem>
  <listitem><para><literal>\b</literal> matches at a word break</para></listitem>
  <listitem><para><literal>\B</literal> matches at a non-word break</para></listitem>
  <listitem><para><literal>\b</literal> matches at a word boundary</para></listitem>
 </itemizedlist>
 <bridgehead renderas="sect3">One-Character Operators</bridgehead>
 <itemizedlist>
  <listitem><para><literal>.</literal> matches any single character</para></listitem>
  <listitem><para><literal>\d</literal> matches any decimal digit</para></listitem>
  <listitem><para><literal>\D</literal> matches any non-digit</para></listitem>
  <listitem><para><literal>\n</literal> matches the newline character</para></listitem>
  <listitem><para><literal>\s</literal> matches any whitespace character</para></listitem>
  <listitem><para><literal>\S</literal> matches any non-whitespace character</para></listitem>
  <listitem><para><literal>\t</literal> matches a horizontal tab character</para></listitem>
  <listitem><para><literal>\w</literal> matches any word (alphanumeric) character</para></listitem>
  <listitem><para><literal>\W</literal> matches any non-word (alphanumeric)
  character</para></listitem>
  <listitem><para><literal>\\</literal> matches the backslash
  (<quote>\</quote>) character</para></listitem>
 </itemizedlist>
 <bridgehead renderas="sect3">Character Class Operator</bridgehead>
 <itemizedlist>
  <listitem><para><literal>[<replaceable>abc</replaceable>]</literal> matches
  any character in
  the set <replaceable>a</replaceable>, <replaceable>b</replaceable> or
  <replaceable>c</replaceable></para></listitem>
  <listitem><para><literal>[^<replaceable>abc</replaceable>]</literal> matches
  any character not
  in the set <replaceable>a</replaceable>, <replaceable>b</replaceable> or
  <replaceable>c</replaceable></para></listitem>
  <listitem><para><literal>[<replaceable>a-z</replaceable>]</literal> matches
  any character in the
  range <replaceable>a</replaceable> to <replaceable>z</replaceable>, inclusive.
  A leading or trailing dash will be interpreted literally</para></listitem>
 </itemizedlist>
 <bridgehead renderas="sect3">Subexpressions and Backreferences</bridgehead>
 <itemizedlist>
  <listitem><para><literal>(<replaceable>abc</replaceable>)</literal> matches
  whatever the expression
  <replaceable>abc</replaceable> would match, and saves it as a subexpression.
  Also used for grouping</para></listitem>
  <listitem><para><literal>(?:<replaceable>...</replaceable>)</literal> pure
  grouping operator, does not
  save contents</para></listitem>
  <listitem><para><literal>(?#<replaceable>...</replaceable>)</literal> embedded
  comment, ignored by engine</para></listitem>
  <listitem><para><literal>(?=<replaceable>...</replaceable>)</literal> positive
  lookahead; the regular expression will match if the text in the brackets
  matches, but that text will not be considered part of the match</para></listitem>
  <listitem><para><literal>(?!<replaceable>...</replaceable>)</literal> negative
  lookahead; the regular expression will match if the text in the brackets
  does not
  match, and that text will not be considered part of the match</para></listitem>
  <listitem><para><literal>\<replaceable>n</replaceable></literal> where 0 &lt;
  <replaceable>n</replaceable> &lt; 10,
  matches the same thing the <replaceable>n</replaceable>th
  subexpression matched. Can only be used in the search string</para></listitem>
  <listitem><para><literal>$<replaceable>n</replaceable></literal> where 0 &lt;
  <replaceable>n</replaceable> &lt; 10,
  substituted with the text matched by the <replaceable>n</replaceable>th
  subexpression. Can only be used in the replacement string</para></listitem>
 </itemizedlist>
 <bridgehead renderas="sect3">Branching (Alternation) Operator</bridgehead>
 <itemizedlist>
  <listitem><para><literal><replaceable>a</replaceable>|<replaceable>b</replaceable></literal>
  matches whatever the expression <replaceable>a</replaceable> would match, or whatever
  the expression <replaceable>b</replaceable> would match.</para></listitem>
 </itemizedlist>
 <bridgehead renderas="sect3">Repeating Operators</bridgehead>
 <para>
  These symbols operate on the previous atomic expression.
 </para>
 <itemizedlist>
  <listitem><para><literal>?</literal> matches the preceding expression or the
  null string</para></listitem>
  <listitem><para><literal>*</literal> matches the null string or any number of repetitions
  of the preceding expression</para></listitem>
  <listitem><para><literal>+</literal> matches one or more repetitions of the preceding
  expression</para></listitem>
  <listitem><para><literal>{<replaceable>m</replaceable>}</literal> matches exactly
  <replaceable>m</replaceable>
  repetitions of the one-character expression</para></listitem>
  <listitem><para><literal>{<replaceable>m</replaceable>,<replaceable>n</replaceable>}</literal>
  matches between
  <replaceable>m</replaceable> and <replaceable>n</replaceable> repetitions of the preceding
  expression, inclusive</para></listitem>
  <listitem><para><literal>{<replaceable>m</replaceable>,}</literal> matches
  <replaceable>m</replaceable> or more
  repetitions of the preceding expression</para></listitem>
 </itemizedlist>
 <bridgehead renderas="sect3">Stingy (Minimal) Matching</bridgehead>
 <para>
  If a repeating operator (above) is immediately followed by a
  <literal>?</literal>, the repeating operator will stop at the smallest
  number of repetitions that can complete the rest of the match.
 </para>
</appendix>