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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 10] 10.10 Simulated Bourne Shell Functions and Aliases </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="1998-08-04T21:36:00Z"><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="ch10_01.htm"TITLE="10. Aliases"><LINKREL="prev"HREF="ch10_09.htm"TITLE="10.9 Shell Functions "><LINKREL="next"HREF="ch11_01.htm"TITLE="11. The Lessons of History"></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="ch10_09.htm"TITLE="10.9 Shell Functions "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 10.9 Shell Functions "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 10<BR>Aliases</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="CHAPTER"HREF="ch11_01.htm"TITLE="11. The Lessons of History"><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 11. The Lessons of History"BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-0227">10.10 Simulated Bourne Shell Functions and Aliases </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-12246"></A><ACLASS="indexterm"NAME="AUTOID-12249"></A><ACLASS="indexterm"NAME="AUTOID-12252"></A><ACLASS="indexterm"NAME="AUTOID-12255"></A><ACLASS="indexterm"NAME="AUTOID-12258"></A>If you have a Bourne shell with no<SPANCLASS="link">functions (<ACLASS="linkend"HREF="ch10_09.htm"TITLE="Shell Functions ">10.9</A>)</SPAN>or<SPANCLASS="link">aliases (<ACLASS="linkend"HREF="ch10_02.htm"TITLE="Aliases for Common Commands ">10.2</A>)</SPAN>,you can do a lot of the same things with shell variables and 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.</P><PCLASS="para">Let's look at an example.<ACLASS="indexterm"NAME="AUTOID-12266"></A>First, here's a shell function named <EMCLASS="emphasis">scp</EM> (safe copy).If the destination file exists and isn't empty, the function prints anerror message instead of copying:</P><PCLASS="para"><TABLECLASS="screen.co"BORDER="1"><TR><THVALIGN="TOP"><PRECLASS="calloutlist"> <ACLASS="co"HREF="ch44_20.htm"TITLE="44.20 test: Testing Files and Strings ">test</A> </PRE></TH><TDVALIGN="TOP"><PRECLASS="screen">scp(){ if test ! -s "$2" then cp "$1" "$2" else echo "scp: cannot copy $1: $2 exists" fi}</PRE></TD></TR></TABLE></P><PCLASS="para">If you use the same <EMCLASS="emphasis">scp</EM> twice, the first time you'll make <EMCLASS="emphasis">bfile</EM>.The second time you try, you see the error:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">$ <CODECLASS="userinput"><B>scp afile bfile</B></CODE> ...$ <CODECLASS="userinput"><B>scp afile bfile</B></CODE>scp: cannot copy afile: bfile exists</PRE></BLOCKQUOTE></P><PCLASS="para">Here's the same <EMCLASS="emphasis">scp</EM>-stored in a shell variable instead of a function:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">scp='if test ! -s "$2"then cp "$1" "$2"else echo "scp: cannot copy $1: $2 exists"fi'</PRE></BLOCKQUOTE></P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-12284"></A>Because this fake function uses shell parameters, you have to add an extrastep: setting the parameters.Simpler functions are easier to use:</P><PCLASS="para"><TABLECLASS="screen.co"BORDER="1"><TR><THVALIGN="TOP"><PRECLASS="calloutlist"><ACLASS="co"HREF="ch44_19.htm"TITLE="44.19 The Bourne Shell set Command ">set</A> </PRE></TH><TDVALIGN="TOP"><PRECLASS="screen">$ <CODECLASS="userinput"><B>set afile bfile</B></CODE>$ <CODECLASS="userinput"><B>eval "$scp"</B></CODE> ...$ <CODECLASS="userinput"><B>eval "$scp"</B></CODE>scp: cannot copy afile: bfile exists</PRE></TD></TR></TABLE></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="ch10_09.htm"TITLE="10.9 Shell Functions "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 10.9 Shell Functions "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="CHAPTER"HREF="ch11_01.htm"TITLE="11. The Lessons of History"><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 11. The Lessons of History"BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">10.9 Shell Functions </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">11. 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