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<HTML><HEAD><TITLE>Recipe 1.3. Exchanging Values Without Using Temporary Variables (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="1999-07-02T01:28:48Z"><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="ch01_01.htm"TITLE="1. Strings"><LINKREL="prev"HREF="ch01_03.htm"TITLE="1.2. Establishing a Default Value"><LINKREL="next"HREF="ch01_05.htm"TITLE="1.4. Converting Between ASCII Characters and Values"></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="ch01_03.htm"TITLE="1.2. Establishing a Default Value"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 1.2. Establishing a Default Value"BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1"><ACLASS="chapter"REL="up"HREF="ch01_01.htm"TITLE="1. Strings"></A></FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch01_05.htm"TITLE="1.4. Converting Between ASCII Characters and Values"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 1.4. Converting Between ASCII Characters and Values"BORDER="0"></A></TD></TR></TABLE></DIV><DIVCLASS="sect1"><H2CLASS="sect1"><ACLASS="title"NAME="ch01-chap01_exchanging_0">1.3. Exchanging Values Without Using Temporary Variables</A></H2><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch01-pgfId-391">Problem<ACLASS="indexterm"NAME="ch01-idx-1000010182-0"></A><ACLASS="indexterm"NAME="ch01-idx-1000010182-1"></A><ACLASS="indexterm"NAME="ch01-idx-1000010182-2"></A></A></H3><PCLASS="para">You want to exchange the values of two scalar variables, but don't want to use a temporary variable.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch01-pgfId-397">Solution</A></H3><PCLASS="para">Use <ACLASS="indexterm"NAME="ch01-idx-1000010188-0"></A><ACLASS="indexterm"NAME="ch01-idx-1000010188-1"></A>list assignment to reorder the variables.</P><PRECLASS="programlisting">($VAR1, $VAR2) = ($VAR2, $VAR1);</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch01-pgfId-405">Discussion</A></H3><PCLASS="para">Most programming languages force you to use an intermediate step when swapping two variables' values:</P><PRECLASS="programlisting">$temp = $a;$a = $b;$b = $temp;</PRE><PCLASS="para"><ACLASS="indexterm"NAME="ch01-idx-1000010189-0"></A>Not so in Perl. It tracks both sides of the assignment, guaranteeing that you don't accidentally clobber any of your values. This lets you eliminate the temporary variable:</P><PRECLASS="programlisting">$a = "alpha";$b = "omega";($a, $b) = ($b, $a); # the first shall be last -- and versa vice</PRE><PCLASS="para">You can even exchange more than two variables at once:</P><PRECLASS="programlisting">($alpha, $beta, $production) = qw(January March August);# move beta to alpha,# move production to beta,# move alpha to production($alpha, $beta, $production) = ($beta, $production, $alpha);</PRE><PCLASS="para">When this code finishes, <CODECLASS="literal">$alpha</CODE>, <CODECLASS="literal">$beta</CODE>, and <CODECLASS="literal">$production</CODE> have the values "<CODECLASS="literal">March</CODE>", "<CODECLASS="literal">August</CODE>", and "<CODECLASS="literal">January</CODE>".</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch01-pgfId-439">See Also</A></H3><PCLASS="para">The section on "List value constructors" in <EMCLASS="emphasis">perldata </EM>(1) and <ACLASS="olink"HREF="../prog/ch02_01.htm">Chapter 2</A> of <ACLASS="citetitle"HREF="../prog/index.htm"TITLE="Programming Perl"><CITECLASS="citetitle">Programming Perl</CITE></A><ACLASS="indexterm"NAME="ch01-idx-1000010184-0"></A><ACLASS="indexterm"NAME="ch01-idx-1000010184-1"></A><ACLASS="indexterm"NAME="ch01-idx-1000010184-2"></A><ACLASS="indexterm"NAME="ch01-idx-1000010184-3"></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="ch01_03.htm"TITLE="1.2. 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