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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 46] 46.3 Bourne Shell Debugger Shows a Shell Variable </TITLE><METANAME="DC.title"CONTENT="UNIX Power Tools"><METANAME="DC.creator"CONTENT="Jerry Peek, Tim O'Reilly & Mike Loukides"><METANAME="DC.publisher"CONTENT="O'Reilly & 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_02.htm"TITLE="46.2 Quoting Trouble? Think, Then Use echo "><LINKREL="next"HREF="ch46_04.htm"TITLE="46.4 Stop Syntax Errors in Numeric Tests "></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_02.htm"TITLE="46.2 Quoting Trouble? Think, Then Use echo "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 46.2 Quoting Trouble? Think, Then Use echo "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_04.htm"TITLE="46.4 Stop Syntax Errors in Numeric Tests "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 46.4 Stop Syntax Errors in Numeric Tests "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-0229">46.3 Bourne Shell Debugger Shows a Shell Variable </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-55540"></A><ACLASS="indexterm"NAME="AUTOID-55543"></A>If you have a shell script that sets several variables and you want toshow the value of one of them, you can add<SPANCLASS="link"> a loop that asks you forvariable names and displays their values : (<ACLASS="linkend"HREF="ch45_19.htm"TITLE="A while Loop with Several Loop Control Commands ">45.19</A>)</SPAN></P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>cat myscript</B></CODE>#!/bin/sh ...while echo "Pick a variable; just RETURN quits: \c" read vardo case "$var" in "") break ;; *) eval echo \$$var ;; esacdone</PRE></BLOCKQUOTE></P><PCLASS="para">The loop prompts <CODECLASS="literal">Pick a variable:</CODE>, then reads a value;if you type an empty answer, the loop quits.Otherwise, the value of that variable is displayed; the<SPANCLASS="link"><EMCLASS="emphasis">eval</EM> (<ACLASS="linkend"HREF="ch08_10.htm"TITLE="eval: When You Need Another Chance ">8.10</A>)</SPAN>command scans the <EMCLASS="emphasis">echo</EM> command line twice.</P><PCLASS="para">This tip isn't just good for debugging.It's good in any shell script where you need to show the value of a variableby typing its name.</P><DIVCLASS="sect1info"><PCLASS="SECT1INFO">- <SPANCLASS="authorinitials">JP</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_02.htm"TITLE="46.2 Quoting Trouble? 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