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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 44] 44.12 Trapping Exits Caused by Interrupts </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="1998-08-04T21:53:45Z"><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="ch44_01.htm"TITLE="44. Shell Programming for the Uninitiated"><LINKREL="prev"HREF="ch44_11.htm"TITLE="44.11 Set Exit Status of a Shell (Script) "><LINKREL="next"HREF="ch44_13.htm"TITLE="44.13 read: Reading from the Keyboard "></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="ch44_11.htm"TITLE="44.11 Set Exit Status of a Shell (Script) "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 44.11 Set Exit Status of a Shell (Script) "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 44<BR>Shell Programming for the Uninitiated</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch44_13.htm"TITLE="44.13 read: Reading from the Keyboard "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 44.13 read: Reading from the Keyboard "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-7120">44.12 Trapping Exits Caused by Interrupts </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-50988"></A><ACLASS="indexterm"NAME="AUTOID-50991"></A>If you're running a shell script and you press your<SPANCLASS="link">interrupt key (<ACLASS="linkend"HREF="ch05_09.htm"TITLE="Setting Your Erase, Kill, and Interrupt Characters ">5.9</A>)</SPAN>(like CTRL-c),the shell quits right away.That can be a problem if you use temporary files in your scriptbecause the sudden exit might leave the temporary files there.The <EMCLASS="emphasis">trap</EM> command lets you tell the shell what to do before it exits.A <EMCLASS="emphasis">trap</EM> can be used for a normal exit, too.See<ACLASS="xref"HREF="ch44_12.htm#UPT-ART-7120-TAB-0"TITLE="Some UNIX Signal Numbers for trap Commands">Table 44.1</A>.</P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-50998"></A><ACLASS="indexterm"NAME="AUTOID-51001"></A><ACLASS="indexterm"NAME="AUTOID-51004"></A>Here's a script named <EMCLASS="emphasis">zpg</EM> that uses a temporary file named<EMCLASS="emphasis">/tmp/zpg$$</EM> in a<SPANCLASS="link">system temporary-file directory (<ACLASS="linkend"HREF="ch21_03.htm"TITLE="Unique Names for Temporary Files ">21.3</A>)</SPAN>.The shell will replace <CODECLASS="literal">$$</CODE> with its<SPANCLASS="link">process ID number (<ACLASS="linkend"HREF="ch38_03.htm"TITLE="Managing Processes: Overall Concepts ">38.3</A>)</SPAN>.Because no other process will have the same ID number, that fileshould have a unique name.The script<SPANCLASS="link">uncompresses (<ACLASS="linkend"HREF="ch24_07.htm"TITLE="Compressing Files to Save Space ">24.7</A>)</SPAN>the file named on its command line, then starts the<EMCLASS="emphasis">pg</EM> file viewer.[3]The script uses <EMCLASS="emphasis">trap</EM>s - so it will clean up the temporary files,even if the userpressesCTRL-c.The script also sets a default exit status of 1 that's reset to 0 if<EMCLASS="emphasis">pg</EM> quitson its own (without an interrupt).</P><BLOCKQUOTECLASS="footnote"><PCLASS="para">[3] The script could run <CODECLASS="literal">gzcat $1 | pg</CODE> directly, but some versionsof <EMCLASS="emphasis">pg</EM> can't back up when reading from a pipe.</P></BLOCKQUOTE><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-51021"></A><ACLASS="indexterm"NAME="AUTOID-51024"></A><TABLECLASS="screen.co"BORDER="1"><TR><THVALIGN="TOP"><PRECLASS="calloutlist"> <ACLASS="co"HREF="ch44_11.htm"TITLE="44.11 Set Exit Status of a Shell (Script) ">exit</A> </PRE></TH><TDVALIGN="TOP"><PRECLASS="screen">#!/bin/sh# zpg - UNCOMPRESS FILE, DISPLAY WITH pg# Usage: zpg filestat=1 # DEFAULT EXIT STATUS; RESET TO 0 BEFORE NORMAL EXITtemp=/tmp/zpg$$trap 'rm -f $temp; exit $stat' 0trap 'echo "`basename $0`: Ouch! Quitting early." 1>&2' 1 2 15case $# in1) gzcat "$1" >$temp pg $temp stat=0 ;;*) echo "Usage: `basename $0` filename" 1>&2 ;;esac</PRE></TD></TR></TABLE></P><ACLASS="indexterm"NAME="AUTOID-51029"></A><ACLASS="indexterm"NAME="AUTOID-51032"></A><PCLASS="para">There are two <EMCLASS="emphasis">trap</EM>s in the script:</P><ULCLASS="itemizedlist"><LICLASS="listitem"><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-51040"></A><ACLASS="indexterm"NAME="AUTOID-51043"></A>The first <EMCLASS="emphasis">trap</EM>, ending with the number <CODECLASS="literal">0</CODE>, is executed for all shellexits - normal or interrupted.It runs the command line between the single quotes.In this example, there are two commands separated with a<SPANCLASS="link">semicolon (<CODECLASS="literal">;</CODE>) (<ACLASS="linkend"HREF="ch08_05.htm"TITLE="Command-Line Evaluation ">8.5</A>)</SPAN>.The first commandremoves the temporary file (using the<SPANCLASS="link"><EMCLASS="emphasis">-f</EM> option (<ACLASS="linkend"HREF="ch23_10.htm"TITLE="Deletion with Prejudice: rm -f ">23.10</A>)</SPAN>,so <EMCLASS="emphasis">rm</EM> won'tgive an error message if the file doesn't exist yet).The second command exits with the value stored in the <EMCLASS="emphasis">stat</EM> shellvariable.Look ahead at the rest of the script-<CODECLASS="literal">$stat</CODE> will always be 1 unlessthe <EMCLASS="emphasis">pg</EM> command quit on its own, in which case <EMCLASS="emphasis">stat</EM> will be resetto 0.Therefore, this shell script will always return the right exit status - if it'sinterrupted before it finishes, it'll return 1; otherwise, 0.[4]</P><BLOCKQUOTECLASS="footnote"><PCLASS="para">[4] It's important to use single quotes, rather than double quotes, around the <EMCLASS="emphasis">trap</EM>.That way, the value of <CODECLASS="literal">$stat</CODE> won't be interpreted until the trap isactually executed when the script exits.</P></BLOCKQUOTE></LI><LICLASS="listitem"><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-51063"></A><ACLASS="indexterm"NAME="AUTOID-51065"></A><ACLASS="indexterm"NAME="AUTOID-51068"></A>The second <EMCLASS="emphasis">trap</EM> has the numbers <CODECLASS="literal">1</CODE> <CODECLASS="literal">2</CODE> <CODECLASS="literal">15</CODE> at the end.These are signal numbers that correspond to different kinds of interrupts.On newer shells, you can use signal names instead of the numbers.There's a short listin<ACLASS="xref"HREF="ch44_12.htm#UPT-ART-7120-TAB-0"TITLE="Some UNIX Signal Numbers for trap Commands">Table 44.1</A>.For a list of all signals, type <CODECLASS="literal">kill -l</CODE> (lowercase "L")or see your online <EMCLASS="emphasis">signal</EM>(3) reference page.</P><PCLASS="para">This trap is done on an abnormal exit (likeCTRL-c).It prints a message, but it could run any list of commands.</P></LI></UL><TABLECLASS="table"><CAPTIONCLASS="table"><ACLASS="title"NAME="UPT-ART-7120-TAB-0">Table 44.1: Some UNIX Signal Numbers for trap Commands</A></CAPTION><THEADCLASS="thead"><TRCLASS="row"VALIGN="TOP"><THCLASS="entry"ALIGN="LEFT"ROWSPAN="1"COLSPAN="1">Signal Number</TH><THCLASS="entry"ALIGN="LEFT"ROWSPAN="1"COLSPAN="1">Signal Name</TH><THCLASS="entry"ALIGN="LEFT"ROWSPAN="1"COLSPAN="1">Explanation</TH></TR></THEAD><TBODYCLASS="tbody"><TRCLASS="row"VALIGN="TOP"><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">0</TD><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">EXIT</TD><TDCLASS="entry"ROWSPAN="1"COLSPAN="1"><EMCLASS="emphasis">exit</EM> command</TD></TR><TRCLASS="row"VALIGN="TOP"><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">1</TD><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">HUP</TD><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">When session disconnected</TD></TR><TRCLASS="row"VALIGN="TOP"><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">2</TD><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">INT</TD><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">Interrupt - often CTRL-c</TD></TR><TRCLASS="row"VALIGN="TOP"><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">3</TD><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">QUIT</TD><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">Quit - often CTRL-\</TD></TR><TRCLASS="row"VALIGN="TOP"><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">15</TD><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">TERM</TD><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">From <EMCLASS="emphasis">kill</EM> command</TD></TR></TBODY></TABLE><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-51111"></A>Shell scripts don't always have two <EMCLASS="emphasis">trap</EM>s.Look at the<SPANCLASS="link"><EMCLASS="emphasis">nom</EM> (<ACLASS="linkend"HREF="ch15_09.htm"TITLE="nom: List Files that Don't Match a Wildcard ">15.9</A>)</SPAN>script for an example.</P><PCLASS="para">I usually don't trap signal 3 (QUIT) in scripts that I usemyself.That gives me an easy way to abort the script without springingthe trap (removing temporary files, etc.).In scripts for general use, though, I usually do trap it.</P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-51119"></A><ACLASS="indexterm"NAME="AUTOID-51122"></A>Also, notice that the <EMCLASS="emphasis">echo</EM> commands in the script have<SPANCLASS="link"><CODECLASS="literal">1>&2</CODE> (<ACLASS="linkend"HREF="ch45_21.htm"TITLE="n>&m: Swap Standard Output and Standard Error ">45.21</A>)</SPAN>at the end.That tells the Bourne shell to put the output of the <EMCLASS="emphasis">echo</EM> command on thestandard error instead of the standard output.This is a good idea because it helps to make sure that errors come to yourscreen instead of being redirected to a file or down a pipe with theother standard output text.(In this particular script, that doesn't matter much because the script is usedinteractively.But it's a goodhabit to get into for all of your scripts.)</P><PCLASS="para">If your <EMCLASS="emphasis">trap</EM> runs a series of commands, it's probably neaterto call a<SPANCLASS="link">shell function (<ACLASS="linkend"HREF="ch10_09.htm"TITLE="Shell Functions ">10.9</A>)</SPAN>than a list of commands:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">trap <CODECLASS="replaceable"><I>funcname</I></CODE> 1 2 15</PRE></BLOCKQUOTE></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="ch44_11.htm"TITLE="44.11 Set Exit Status of a Shell (Script) "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 44.11 Set Exit Status of a Shell (Script) "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="ch44_13.htm"TITLE="44.13 read: Reading from the Keyboard "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 44.13 read: Reading from the Keyboard "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">44.11 Set Exit Status of a Shell (Script) </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">44.13 read: Reading from the Keyboard </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 & 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>⌨️ 快捷键说明
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