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trapping error in bash script 'trap error ERR'

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Trapping errors in bash scripts is a little easier if you make use of the "trap function ERR" ability. From the bash man page:

If a sigspec is ERR, the command arg is executed whenever a simple
command has a non-zero  exit  status.  The ERR trap is not executed
if the failed command is part of an until or while loop, part of
an if statement, part of a && or  ||  list, or if the command's
return value is being inverted via !.
 

You'd use it in a script like this:

function error {
echo Error
exit 1
}
trap error ERR
# commands that may have non-zero exit follow
 

This post was prompted by the following newsgroup post:

From: "Wilson" <mr.sean.wil...@gmail.com>
Newsgroups: comp.os.linux.misc
Subject: Error handling in bash scripts
Date: 1 Feb 2005 16:35:35 -0800
Organization: http://groups.google.com
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Hi,

I'm trying my hand at bash script programming and was wondering how to
make my scripts more robust. For example, I have one bash script that
runs daily that makes an incremental backup of my hard-disk and rotates
the daily backups. If this fails, I want the script to send me an email
to let me know something went wrong. This means that every line in the
program that can possibly fail must call a "error" function that sends
an email. Here's an examples of what I have so far:

function error {
echo Failed.
ls -l $SNAPSHOT | mail seanw -s "Backup script failed"
exit
}

if [ -d $BACKUP_NAME.0 ]; then
echo Creating copy of newest backup...
rm -rf $TEMP_BACKUP || error
cp -al $BACKUP_NAME.0 $TEMP_BACKUP || error
echo Updating newest backup copy with rsync...
else
echo No previous backups found. Creating first full backup...
fi

rsync -av --delete-after --delete-excluded \
--exclude=$EXCLUDES $TO_BACKUP $TEMP_BACKUP || error

# snipped the rest...

This works fine, but I need to remember to add the "|| error" snippet
to the end of every command, it looks messy, clutters my code and I
might forget it to do it everywhere. Is there any better way to do
error handling in bash? For example, can I define a function that will
be called when the script fails or use C++ style exceptions? I noticed
that when running Makefiles, make will immediately exit if one of the
commands fail. That's similar to what I'm after, but I need to call a
function on failure.

Newsgroups: comp.os.linux.misc
From: Stephane CHAZELAS <this.addr...@is.invalid>
Subject: Re: Error handling in bash scripts
References: <1107304535.119267.126770@c13g2000cwb.googlegroups.com> <36amlfF507vhuU1@individual.net>
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Date: Wed, 2 Feb 2005 08:52:24 +0000
Lines: 10
Organization: Guest of ProXad - France
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2005-02-2, 00:54(+00), Chris F.A. Johnson:
[...]
>     Would "trap error DEBUG" do what you want?

You were probably thinking of:

trap error ERR

-- 
Stéphane

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