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258 lines
8.7 KiB
HTML
258 lines
8.7 KiB
HTML
<HTML>
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<HEAD>
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<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
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<META NAME="Author" CONTENT="lloyd tabb">
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<META NAME="GENERATOR" CONTENT="Mozilla/4.0 [en] (WinNT; I) [Netscape]">
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<TITLE>Regular expressions in the cvs query tool</TITLE>
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</HEAD>
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<BODY>
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<H1>
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Description of MySQL regular expression syntax.</H1>
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Regular expressions are a powerful way of specifying complex searches.
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<P><B>MySQL</B> uses Henry Spencer's implementation of regular expressions.
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And that is aimed to conform to POSIX 1003.2. <B>MySQL</B> uses the extended
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version.
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<P>To get more exact information see Henry Spencer's regex.7 manual.
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<P>This is a simplistic reference that skips the details. From here on
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a regular expression is called a regexp.
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<P>A regular expression describes a set of strings. The simplest case is
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one that has no special characters in it. For example the regexp <TT>hello</TT>
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matches <TT>hello</TT> and nothing else.
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<P>Nontrivial regular expressions use certain special constructs so that
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they can match more than one string. For example, the regexp <TT>hello|word</TT>
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matches either the string <TT>hello</TT> or the string <TT>word</TT>.
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<P>And a more complex example regexp <TT>B[an]*s</TT> matches any of the
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strings <TT>Bananas</TT>, <TT>Baaaaas</TT>, <TT>Bs</TT> and all other string
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starting with a <TT>B</TT> and continuing with any number of <TT>a</TT>
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<TT>n</TT> and ending with a <TT>s</TT>.
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<P>The following special characters/constructs are known.
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<DL COMPACT>
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<DT>
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<TT>^</TT></DT>
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<DD>
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Start of whole string.</DD>
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<PRE>mysql> select "fo\nfo" regexp "^fo$"; -> 0
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mysql> select "fofo" regexp "^fo"; -> 1</PRE>
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<DT>
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<TT>$</TT></DT>
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<DD>
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End of whole string.</DD>
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<PRE>mysql> select "fo\no" regexp "^fo\no$"; -> 1
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mysql> select "fo\no" regexp "^fo$"; -> 0</PRE>
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<DT>
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<TT>.</TT></DT>
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<DD>
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Any character (including newline).</DD>
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<PRE>mysql> select "fofo" regexp "^f.*"; -> 1
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mysql> select "fo\nfo" regexp "^f.*"; -> 1</PRE>
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<DT>
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<TT>a*</TT></DT>
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<DD>
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Any sequence of zero or more a's.</DD>
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<PRE>mysql> select "Ban" regexp "^Ba*n"; -> 1
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mysql> select "Baaan" regexp "^Ba*n"; -> 1
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mysql> select "Bn" regexp "^Ba*n"; -> 1</PRE>
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<DT>
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<TT>a+</TT></DT>
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<DD>
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Any sequence of one or more a's.</DD>
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<PRE>mysql> select "Ban" regexp "^Ba+n"; -> 1
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mysql> select "Bn" regexp "^Ba+n"; -> 0</PRE>
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<DT>
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<TT>a?</TT></DT>
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<DD>
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Either zero or one a.</DD>
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<PRE>mysql> select "Bn" regexp "^Ba?n"; -> 1
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mysql> select "Ban" regexp "^Ba?n"; -> 1
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mysql> select "Baan" regexp "^Ba?n"; -> 0</PRE>
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<DT>
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<TT>de|abc</TT></DT>
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<DD>
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Either the sequence <TT>de</TT> or <TT>abc</TT>.</DD>
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<PRE>mysql> select "pi" regexp "pi|apa"; -> 1
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mysql> select "axe" regexp "pi|apa"; -> 0
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mysql> select "apa" regexp "pi|apa"; -> 1
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mysql> select "apa" regexp "^(pi|apa)$"; -> 1
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mysql> select "pi" regexp "^(pi|apa)$"; -> 1
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mysql> select "pix" regexp "^(pi|apa)$"; -> 0</PRE>
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<DT>
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<TT>(abc)*</TT></DT>
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<DD>
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Zero or more times the sequence <TT>abc</TT>.</DD>
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<PRE>mysql> select "pi" regexp "^(pi)+$"; -> 1
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mysql> select "pip" regexp "^(pi)+$"; -> 0
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mysql> select "pipi" regexp "^(pi)+$"; -> 1</PRE>
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<DT>
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<TT>{1}</TT></DT>
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<DT>
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<TT>{2,3}</TT></DT>
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<DD>
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There is a more general way of writing regexps that match many occurrences.</DD>
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<DL COMPACT>
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<DT>
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<TT>a*</TT></DT>
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<DD>
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Can be written as <TT>a{0,}</TT>.</DD>
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<DT>
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<TT>+</TT></DT>
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<DD>
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Can be written as <TT>a{1,}</TT>.</DD>
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<DT>
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<TT>?</TT></DT>
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<DD>
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Can be written as <TT>a{0,1}</TT>.</DD>
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</DL>
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To be more precise, an atom followed by a bound containing one integer <TT>i</TT>
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and no comma matches a sequence of exactly <TT>i</TT> matches of the atom.
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An atom followed by a bound containing one integer <TT>i</TT> and a comma
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matches a sequence of <TT>i</TT> or more matches of the atom. An atom followed
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by a bound containing two integers <TT>i</TT> and <TT>j</TT> matches a
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sequence of <TT>i</TT> through <TT>j</TT> (inclusive) matches of the atom.
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Both arguments must <TT>0 >= value <= RE_DUP_MAX (default 255)</TT>,
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and if there are two of them, the second must be bigger or equal to the
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first.
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<DT>
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<TT>[a-dX]</TT></DT>
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<DT>
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<TT>[^a-dX]</TT></DT>
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<DD>
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Any character which is (not if ^ is used) either <TT>a</TT>, <TT>b</TT>,
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<TT>c</TT>, <TT>d</TT> or <TT>X</TT>. To include <TT>]</TT> it has to be
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written first. To include <TT>-</TT> it has to be written first or last.
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So <TT>[0-9]</TT> matches any decimal digit. All character that does not
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have a defined meaning inside a <TT>[]</TT> pair has no special meaning
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and matches only itself.</DD>
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<PRE>mysql> select "aXbc" regexp "[a-dXYZ]"; -> 1
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mysql> select "aXbc" regexp "^[a-dXYZ]$"; -> 0
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mysql> select "aXbc" regexp "^[a-dXYZ]+$"; -> 1
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mysql> select "aXbc" regexp "^[^a-dXYZ]+$"; -> 0
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mysql> select "gheis" regexp "^[^a-dXYZ]+$"; -> 1
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mysql> select "gheisa" regexp "^[^a-dXYZ]+$"; -> 0</PRE>
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<DT>
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<TT>[[.characters.]]</TT></DT>
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<DD>
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The sequence of characters of that collating element. The sequence is a
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single element of the bracket expression's list. A bracket expression containing
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a multi-character collating element can thus match more than one character,
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e.g. if the collating sequence includes a <TT>ch</TT> collating element,
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then the RE <TT>[[.ch.]]*c</TT> matches the first five characters of <TT>chchcc</TT>.</DD>
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<DT>
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<TT>[=character-class=]</TT></DT>
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<DD>
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An equivalence class, standing for the sequences of characters of all collating
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elements equivalent to that one, including itself. For example, if <TT>o</TT>
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and <TT>(+)</TT> are the members of an equivalence class, then <TT>[[=o=]]</TT>,
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<TT>[[=(+)=]]</TT>, and <TT>[o(+)]</TT> are all synonymous. An equivalence
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class may not be an endpoint of a range.</DD>
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<DT>
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<TT>[:character_class:]</TT></DT>
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<DD>
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Within a bracket expression, the name of a character class enclosed in
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<TT>[:</TT> and <TT>:]</TT> stands for the list of all characters belonging
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to that class. Standard character class names are:</DD>
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<TABLE BORDER WIDTH="100%" NOSAVE >
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<TR>
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<TD>alnum </TD>
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<TD>digit </TD>
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<TD>punct </TD>
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</TR>
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<TR>
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<TD>alpha </TD>
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<TD>graph </TD>
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<TD>space </TD>
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</TR>
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<TR>
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<TD>blank </TD>
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<TD>lower </TD>
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<TD>upper </TD>
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</TR>
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<TR>
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<TD>cntrl </TD>
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<TD>print </TD>
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<TD>xdigit </TD>
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</TR>
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</TABLE>
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These stand for the character classes defined in ctype(3). A locale may
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provide others. A character class may not be used as an endpoint of a range.
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<PRE>mysql> select "justalnums" regexp "[[:alnum:]]+"; -> 1
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mysql> select "!!" regexp "[[:alnum:]]+"; -> 0</PRE>
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<LI>
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[[:<:]]</LI>
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<LI>
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[[:>:]] These match the null string at the beginning and end of a word
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respectively. A word is defined as a sequence of word characters which
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is neither preceded nor followed by word characters. A word character is
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an alnum character (as defined by ctype(3)) or an underscore.</LI>
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<PRE>mysql> select "a word a" regexp "[[:<:]]word[[:>:]]"; -> 1
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mysql> select "a xword a" regexp "[[:<:]]word[[:>:]]"; -> 0</PRE>
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</DL>
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<PRE>mysql> select "weeknights" regexp "^(wee|week)(knights|nights)$"; -> 1</PRE>
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</BODY>
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</HTML>
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