Bourne Shell: how to terminate when inner shell command returns nonzero exit code?

Question

I have the following simple shell script:

#   get all servers from config
sshservers=`node $scriptDir/readconfig.js --command cluster.sshservers`

#for each server
for server in sshservers
do

    #run deployserver with server (server:port format) argument
    if ! sh deployserver --server $server
    then
        exit 1 #failure
    fi

done

Now, the node command to get the sshservers may return an exit code that is nonzero. When this happens, things went horribly wrong and so I would like to quit with an error message.

How would I do this? Would this be the most appropriate way?

sshservers=`node $scriptDir/readconfig.js --command cluster.sshservers`
if ! $?
then
    echo "Error: node readconfig tool failed."
    exit 1
fi

Also, how do I output the stderr of this node command when things go so horribly wrong?

Finally, is the way I exit when sh deployserver fails proper, or should this be done differently?

OlivierLi · Accepted Answer · 2013-02-05 01:25:37Z

2

To see if the last command was sucessfull you can do this :

if [ "$?" != "0" ]
    then
        //do something
    fi

The stderr should find it's way to the console you are running the script by itself.

edited Feb 5, 2013 at 1:25

answered May 16, 2012 at 16:55

OlivierLi

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Comments

William Pursell · Accepted Answer · 2012-05-16 17:19:48Z

2

It looks a bit strange, but it is legal to do:

sshservers=$( node ... ) || exit 1

Note that you do not need to emit an error message, since the node command ought to have printed a useful error diagnostic before it exited. You can also simply add set -e at the start of the script, which will cause your script to abort if any assignments of this form terminate. The return value of the assignment is the return value of the "inner" command, so the normal techniques all apply.

answered May 16, 2012 at 17:19

William Pursell

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1 Comment

Jé Queue Over a year ago

Yep, this is clean and a practice that can be seen reflected in Perl.

Tim Pote · Accepted Answer · 2012-05-16 16:56:22Z

1

Use $?, which contains the exit code from the last run command. So you can do:

sshservers=`node $scriptDir/readconfig.js --command cluster.sshservers`
[[ "$?" == "0" ]] || exit 1

The way you exit from sh deployserver is the way I would do it. You could use $? if you want, but the way you have it is shorter and cleaner IMHO.

answered May 16, 2012 at 16:56

Tim Pote

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Comments

glenn jackman · Accepted Answer · 2012-05-16 17:22:20Z

1

You can also put the assignment into an if statement:

if ! sshservers=$(node $scriptDir/readconfig.js --command cluster.sshservers)
then
  echo "oops, node command returned non-zero"
  exit 1
fi

for server in $sshservers; do ...

answered May 16, 2012 at 17:22

glenn jackman

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