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<HEAD><TITLE>Regular Expressions</TITLE></HEAD>
<BODY>
Regular expressions are a way to specify text patterns when searching for
a text in a buffer. Regular expressions consist of normal characters
and special operator characters with a special meanings. Operators
allow you to anchor matches, match classes of characters, match given
pattern several times or match alternate patterns. Operators can be
also used to group patterns.
<H1><A NAME="regexp-search">Search/Match Operators</A></H1>
<DL>
<DT><B>\</B>
<DD>Quotes the following character. If the following character is not
alphanumeric, it will lost it's special meaning, otherwise it will
gain a special meaning as described below.
<DT><B>\n</B>
<DD>Matches a 0x0A (LF) character.
<DT><B>\r</B>
<DD>Matches a 0x0D (CR) character.
<DT><B>\t</B>
<DD>Matches a 0x09 (TAB) character.
<DT><B>\e</B>
<DD>Matches an escape character (0x1B)
<DT><B>\s</B>
<DD>Matches whitespace (CR, LF, TAB, SPACE) characters.
<DT><B>\S</B>
<DD>Matches non-whitespace (the reverse of \s)
<DT><B>\w</B>
<DD>Matches word character [a-zA-Z0-9]
<DT><B>\W</B>
<DD>Matches non-word character
<DT><B>\d</B>
<DD>Matches a digit [0-9].
<DT><B>\D</B>
<DD>Matches a non-digit.
<DT><B>\U</B>
<DD>Matches uppercase characters (A-Z)
<DT><B>\L</B>
<DD>Matches lowercase characters (a-z)
<DT><B>\x##</B>
<DD>Matches specified hex value (\x0A, \x0D, \x09, etc.)
<DT><B>\o###</B>
<DD>Matches specified octal value (\o000, \o015, etc.)
<DT><B>\N###</B>
<DD>Matches specified decimal value (\N000, \N013, \N009, etc.)
<DT><B>\C</B>
<DD>Starts case sensitive matching.
<DT><B>\c</B>
<DD>Starts case insensitive matching.
<DT><B>^</B>
<DD>Match a beginning of line.
<DT><B>$</B>
<DD>Match an end of line.
<DT><B>.</B>
<DD>Match any character.
<DT><B><</B>
<DD>Match beginning of word (word consists of [A-Za-z0-9]).
<DT><B>></B>
<DD>Match end of word.
<DT><B>[ ]</B>
<DD>Specifies a class of characters ([abc123], [\]\x10], etc).
<DT><B>[ - ]</B>
<DD>Specified a range of characters ([0-9a-zA-Z_], [0-9], etc)
<DT><B>[^ ]</B>
<DD>Specifies complement class ([^a-z], [^\-], etc)
<DT><B>?</B>
<DD>Matches preceeding pattern optionally (a?bc, filename\.?, $?, etc)
<DT><B>|</B>
<DD>Matches preceeding or next pattern (a|b, c|d, abc|d). Only one
character will be used as pattern unless grouped together using {} or
().
<DT><B>*</B>
<DD>Match zero or more occurances of preceeding pattern. Matching is
greedy and will match as much as possible.
<DT><B>+</B>
<DD>Match one or more occurances of preceeding pattern. Match is
greedy.
<DT><B>@</B>
<DD>Match zero or more occurances of preceeding pattern. Matching is
non-greedy and will match as little as possible without causing the
rest of the pattern match to fail.
<DT><B>#</B>
<DD>Match one or more occurances of preceeding pattern. Matching is
non-greedy.
<DT><B>{ }</B>
<DD>Group patterns together to form complex pattern. ( {abc},
{abc}|{cde}, {abc}?, {word}?)
<DT><B>( )</B>
<DD>Group patterns together to form complex pattern. Also used to save
the matched substring into the register which can be used for
substitution operation. Up to 9 registers can be used.
</DL>
<H1><A NAME="regexp-replace">Replacement Operators</A></H1>
<DL>
<DT><B>\</B>
<DD>Causes the next character to lose it's special meaning.
<DT><B>\n</B>
<DD>Inserts a 0x0A (LF) character.
<DT><B>\r</B>
<DD>Inserts a 0x0D (CR) character.
<DT><B>\t</B>
<DD>Inserts a 0x09 (TAB) character.
<DT><B>\1 to \9</B>
<DD>Recalls stored substrings from registers (\1, \2, \3, to \9).
<DT><B>\0</B>
<DD>Recalls entire matched pattern.
<DT><B>\u</B>
<DD>Convert next character to uppercase
<DT><B>\l</B>
<DD>Convert next character to lowercase
<DT><B>\U</B>
<DD>Convert to uppercase till \E or \e
<DT><B>\L</B>
<DD>Convert to lowercase till \E or \e
</DL>
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