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<HTML><HEAD><TITLE>Recipe 6.13. Approximate Matching (Perl Cookbook)</TITLE><METANAME="DC.title"CONTENT="Perl Cookbook"><METANAME="DC.creator"CONTENT="Tom Christiansen & Nathan Torkington"><METANAME="DC.publisher"CONTENT="O'Reilly & Associates, Inc."><METANAME="DC.date"CONTENT="1999-07-02T01:34:32Z"><METANAME="DC.type"CONTENT="Text.Monograph"><METANAME="DC.format"CONTENT="text/html"SCHEME="MIME"><METANAME="DC.source"CONTENT="1-56592-243-3"SCHEME="ISBN"><METANAME="DC.language"CONTENT="en-US"><METANAME="generator"CONTENT="Jade 1.1/O'Reilly DocBook 3.0 to HTML 4.0"><LINKREV="made"HREF="mailto:online-books@oreilly.com"TITLE="Online Books Comments"><LINKREL="up"HREF="ch06_01.htm"TITLE="6. Pattern Matching"><LINKREL="prev"HREF="ch06_13.htm"TITLE="6.12. Honoring Locale Settings in Regular Expressions"><LINKREL="next"HREF="ch06_15.htm"TITLE="6.14. Matching from Where the Last Pattern Left Off"></HEAD><BODYBGCOLOR="#FFFFFF"><img alt="Book Home" border="0" src="gifs/smbanner.gif" usemap="#banner-map" /><map name="banner-map"><area shape="rect" coords="1,-2,616,66" href="index.htm" alt="Perl Cookbook"><area shape="rect" coords="629,-11,726,25" href="jobjects/fsearch.htm" alt="Search this book" /></map><div class="navbar"><p><TABLEWIDTH="684"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch06_13.htm"TITLE="6.12. Honoring Locale Settings in Regular Expressions"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 6.12. Honoring Locale Settings in Regular Expressions"BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1"><ACLASS="chapter"REL="up"HREF="ch06_01.htm"TITLE="6. Pattern Matching"></A></FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch06_15.htm"TITLE="6.14. Matching from Where the Last Pattern Left Off"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 6.14. Matching from Where the Last Pattern Left Off"BORDER="0"></A></TD></TR></TABLE></DIV><DIVCLASS="sect1"><H2CLASS="sect1"><ACLASS="title"NAME="ch06-16952">6.13. Approximate Matching</A></H2><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch06-pgfId-1529">Problem<ACLASS="indexterm"NAME="ch06-idx-1000007645-0"></A><ACLASS="indexterm"NAME="ch06-idx-1000007645-1"></A><ACLASS="indexterm"NAME="ch06-idx-1000007645-2"></A><ACLASS="indexterm"NAME="ch06-idx-1000007645-3"></A><ACLASS="indexterm"NAME="ch06-idx-1000007645-4"></A></A></H3><PCLASS="para">You want to match something fuzzily.</P><PCLASS="para">Any time you want to be forgiving of misspellings in user input, you want to do fuzzy matching.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch06-pgfId-1537">Solution</A></H3><PCLASS="para">Use the String::Approx module, available from CPAN:</P><PRECLASS="programlisting">use String::Approx qw(amatch);if (amatch("PATTERN", @list)) { # matched}@matches = amatch("PATTERN", @list);</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch06-pgfId-1557">Discussion</A></H3><PCLASS="para"><ACLASS="indexterm"NAME="ch06-idx-1000007646-0"></A>String::Approx calculates the difference between the pattern and each string in the list. If less than a certain number (by default, 10 percent of the length of the pattern) one-character insertions, deletions, or substitutions are required to make the string from the pattern, the string "matches" the pattern. In scalar context, <CODECLASS="literal">amatch</CODE> returns the number of successful matches. In list context, it returns those strings that matched.</P><PRECLASS="programlisting">use String::Approx qw(amatch);open(DICT, "/usr/dict/words") or die "Can't open dict: $!";while(<DICT>) { print if amatch("balast");}<CODECLASS="userinput"><B><CODECLASS="replaceable"><I>ballast</I></CODE></B></CODE><CODECLASS="userinput"><B><CODECLASS="replaceable"><I>balustrade</I></CODE></B></CODE><CODECLASS="userinput"><B><CODECLASS="replaceable"><I>blast</I></CODE></B></CODE><CODECLASS="userinput"><B><CODECLASS="replaceable"><I>blastula</I></CODE></B></CODE><CODECLASS="userinput"><B><CODECLASS="replaceable"><I>sandblast</I></CODE></B></CODE></PRE><PCLASS="para">You can also pass options to <CODECLASS="literal">amatch</CODE> to control case-insensitivity and the number of insertions, deletions, or substitutions to have. These options are passed in as a list reference; they're fully described in the String::Approx documentation.</P><PCLASS="para">It must be noted that using the module's matching function seems to run between 10 and 40 times slower than Perl's built-in matching function. Only use String::Approx if you're after fuzziness in your matching that Perl's regular expressions can't provide. <ACLASS="indexterm"NAME="ch06-idx-1000007648-0"></A><ACLASS="indexterm"NAME="ch06-idx-1000007648-1"></A><ACLASS="indexterm"NAME="ch06-idx-1000007648-2"></A><ACLASS="indexterm"NAME="ch06-idx-1000007648-3"></A><ACLASS="indexterm"NAME="ch06-idx-1000007648-4"></A><ACLASS="indexterm"NAME="ch06-idx-1000007648-5"></A></P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch06-pgfId-1589">See Also</A></H3><PCLASS="para">The documentation for the CPAN module String::Approx; <ACLASS="xref"HREF="ch01_17.htm"TITLE="Soundex Matching">Recipe 1.16</A></P></DIV></DIV><DIVCLASS="htmlnav"><P></P><HRALIGN="LEFT"WIDTH="684"TITLE="footer"><TABLEWIDTH="684"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch06_13.htm"TITLE="6.12. Honoring Locale Settings in Regular Expressions"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 6.12. Honoring Locale Settings in Regular Expressions"BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><ACLASS="book"HREF="index.htm"TITLE="Perl Cookbook"><IMGSRC="../gifs/txthome.gif"ALT="Perl Cookbook"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch06_15.htm"TITLE="6.14. Matching from Where the Last Pattern Left Off"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 6.14. Matching from Where the Last Pattern Left Off"BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228">6.12. Honoring Locale Settings in Regular Expressions</TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><ACLASS="index"HREF="index/index.htm"TITLE="Book Index"><IMGSRC="../gifs/index.gif"ALT="Book Index"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228">6.14. 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