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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 46] 46.2 Quoting Trouble?  Think, Then Use echo </TITLE><METANAME="DC.title"CONTENT="UNIX Power Tools"><METANAME="DC.creator"CONTENT="Jerry Peek, Tim O'Reilly &amp; Mike Loukides"><METANAME="DC.publisher"CONTENT="O'Reilly &amp; Associates, Inc."><METANAME="DC.date"CONTENT="1998-08-04T21:55:37Z"><METANAME="DC.type"CONTENT="Text.Monograph"><METANAME="DC.format"CONTENT="text/html"SCHEME="MIME"><METANAME="DC.source"CONTENT="1-56592-260-3"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="ch46_01.htm"TITLE="46. Shell Script Debugging and Gotchas"><LINKREL="prev"HREF="ch46_01.htm"TITLE="46.1 Tips for Debugging Shell Scripts "><LINKREL="next"HREF="ch46_03.htm"TITLE="46.3 Bourne Shell Debugger Shows a Shell Variable "></HEAD><BODYBGCOLOR="#FFFFFF"TEXT="#000000"><DIVCLASS="htmlnav"><H1><IMGSRC="gifs/smbanner.gif"ALT="UNIX Power Tools"USEMAP="#srchmap"BORDER="0"></H1><MAPNAME="srchmap"><AREASHAPE="RECT"COORDS="0,0,466,58"HREF="index.htm"ALT="UNIX Power Tools"><AREASHAPE="RECT"COORDS="467,0,514,18"HREF="jobjects/fsearch.htm"ALT="Search this book"></MAP><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch46_01.htm"TITLE="46.1 Tips for Debugging Shell Scripts "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 46.1 Tips for Debugging Shell Scripts "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 46<BR>Shell Script Debugging and Gotchas</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch46_03.htm"TITLE="46.3 Bourne Shell Debugger Shows a Shell Variable "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 46.3 Bourne Shell Debugger Shows a Shell Variable "BORDER="0"></A></TD></TR></TABLE>&nbsp;<HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-0378">46.2 Quoting Trouble?  Think, Then Use echo </A></H2><DIVCLASS="msgset"><DIVCLASS="msgentry"><DIVCLASS="msg"><DIVCLASS="msgtext"><PCLASS="para"><BCLASS="msgentry.role">Q:</B> <ACLASS="indexterm"NAME="AUTOID-55493"></A><ACLASS="indexterm"NAME="AUTOID-55496"></A><ACLASS="indexterm"NAME="AUTOID-55499"></A> I can't get the following shell script to work:</P><PCLASS="para"><BCLASS="msgentry.role">Q:</B> <BLOCKQUOTECLASS="screen"><PRECLASS="screen">case $col2 in&quot;income&quot;) awk '{if($2=='$col2') {   /* THIS LINE IS THE PROBLEM */          /* I CAN'T GET AWK TO RECOGNIZE EITHER '$col2' or '$2' */                .                .          } ' $file1 ;;</PRE></BLOCKQUOTE></P></DIV></DIV></DIV><DIVCLASS="msgentry"><DIVCLASS="msg"><DIVCLASS="msgtext"><PCLASS="para"><BCLASS="msgentry.role">A:</B>  It is clear from this code fragment that <EMCLASS="emphasis">awk</EM> is supposed to compare<CODECLASS="literal">$2</CODE> with <CODECLASS="literal">&quot;income&quot;</CODE>. If you think about it (or change<CODECLASS="literal">awk</CODE> to <CODECLASS="literal">echo</CODE>above), you will see that you have given the following to <EMCLASS="emphasis">awk</EM>:</P><PCLASS="para"><BCLASS="msgentry.role">A:</B> <BLOCKQUOTECLASS="screen"><PRECLASS="screen">{if($2==income) { /* THIS LINE IS THE PROBLEM */</PRE></BLOCKQUOTE></P><PCLASS="para"><BCLASS="msgentry.role">A:</B> What does <EMCLASS="emphasis">awk</EM> do with this? It compares <CODECLASS="literal">$2</CODE> with the contents ofthe variable <EMCLASS="emphasis">income</EM>. If <EMCLASS="emphasis">income</EM> has not been set, it comparesit with zero or with the null string. Instead, you want:</P><PCLASS="para"><BCLASS="msgentry.role">A:</B> <BLOCKQUOTECLASS="screen"><PRECLASS="screen">{ if ($2 == &quot;income&quot;) {</PRE></BLOCKQUOTE></P><PCLASS="para"><BCLASS="msgentry.role">A:</B> which you can say with:</P><PCLASS="para"><BCLASS="msgentry.role">A:</B> <BLOCKQUOTECLASS="screen"><PRECLASS="screen">case $col2 inincome)        awk '        {                if ($2 == &quot;'$col2'&quot;) {                        ... awk code ...                }        }' $file1;;</PRE></BLOCKQUOTE></P></DIV></DIV></DIV></DIV><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-55528"></A><ACLASS="indexterm"NAME="AUTOID-55531"></A>Replacing commands with <CODECLASS="literal">echo</CODE> in shell scripts is a handy debuggingtrick.</P><DIVCLASS="sect1info"><PCLASS="SECT1INFO">- <SPANCLASS="authorinitials">CT</SPAN> <SPANCLASS="bibliomisc">in <ACLASS="systemitem.newsgroup"HREF="news:net.unix">net.unix</A> on Usenet, 1 November 1986</SPAN></P></DIV></DIV><DIVCLASS="htmlnav"><P></P><HRALIGN="LEFT"WIDTH="515"TITLE="footer"><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch46_01.htm"TITLE="46.1 Tips for Debugging Shell Scripts "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 46.1 Tips for Debugging Shell Scripts "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><ACLASS="book"HREF="index.htm"TITLE="UNIX Power Tools"><IMGSRC="gifs/txthome.gif"SRC="gifs/txthome.gif"ALT="UNIX Power Tools"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch46_03.htm"TITLE="46.3 Bourne Shell Debugger Shows a Shell Variable "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 46.3 Bourne Shell Debugger Shows a Shell Variable "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">46.1 Tips for Debugging Shell Scripts </TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><ACLASS="index"HREF="index/idx_0.htm"TITLE="Book Index"><IMGSRC="gifs/index.gif"SRC="gifs/index.gif"ALT="Book Index"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172">46.3 Bourne Shell Debugger Shows a Shell Variable </TD></TR></TABLE><HRALIGN="LEFT"WIDTH="515"TITLE="footer"><IMGSRC="gifs/smnavbar.gif"SRC="gifs/smnavbar.gif"USEMAP="#map"BORDER="0"ALT="The UNIX CD Bookshelf Navigation"><MAPNAME="map"><AREASHAPE="RECT"COORDS="0,0,73,21"HREF="../index.htm"ALT="The UNIX CD Bookshelf"><AREASHAPE="RECT"COORDS="74,0,163,21"HREF="index.htm"ALT="UNIX Power Tools"><AREASHAPE="RECT"COORDS="164,0,257,21"HREF="../unixnut/index.htm"ALT="UNIX in a Nutshell"><AREASHAPE="RECT"COORDS="258,0,321,21"HREF="../vi/index.htm"ALT="Learning the vi Editor"><AREASHAPE="RECT"COORDS="322,0,378,21"HREF="../sedawk/index.htm"ALT="sed &amp; awk"><AREASHAPE="RECT"COORDS="379,0,438,21"HREF="../ksh/index.htm"ALT="Learning the Korn Shell"><AREASHAPE="RECT"COORDS="439,0,514,21"HREF="../lrnunix/index.htm"ALT="Learning the UNIX Operating System"></MAP></DIV></BODY></HTML>
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