Execute a shell command from a shell script without stopping if error occurs

Question

In a sort of try/catch form I want to execute a bash that doesn't stop if an error occurs.

The specific bash is:

#!/bin/sh

invoke-rc.d tomcat stop

rm -fr /var/webapps/
cp -R $WEBAPP /var/webapps/
invoke-rc.d tomcat start

I want to exec "invoke-rc.d tomcat stop" and even if Tomcat is not running, continue to execute the other bash commands.

Isn't that bash's default behavior? I could have sworn it was (you need to take explicit action to terminate a script if some command fails...) — Alex Martelli
– Alex Martelli, Commented Jul 2, 2009 at 15:35
If you execute this script and tomcat is not running the script will stop execution since the first command return error. I want the script to continue. — JorgeO
– JorgeO, Commented Jul 2, 2009 at 15:38
@Alex: it is default but there is probablt something that overrides the default setting. — Milan Babuškov
– Milan Babuškov, Commented Jul 2, 2009 at 16:23
I'm with Alex - bash is misbehaving, or has been configured to (mis)behave by exiting on an error. Use: 'set +e' to counteract the effect of 'set -e' (which means terminate on error). And sort out what it is in your environment setup that makes bash misbehave - all sorts of scripts will fail unexpectedly if your shell bails on the first error. — Jonathan Leffler
– Jonathan Leffler, Commented Jul 2, 2009 at 16:54

score 32 · Accepted Answer · 2010-03-04 03:35:18Z

32

Try:

invoke-rc.d tomcat stop > /dev/null 2>&1 || true

A little background:

user@tower: # true
user@tower: # echo $?
0
user@tower: # false
user@tower: # echo $?
1

user@tower: # which true
/bin/true
user@tower: # which false
/bin/false

The real solution is looking at the tomcat init script to see how it knows if tomcat is running :) That way, you don't pester it needlessly.

See this post on the other suggestion to unset / set +e. While it would solve your immediate problem, you may find that you need the recently unset behavior in your own script, especially since you are copying files.

This is one of the biggest reasons why true and false were made, other than making Makefiles behave as expected in a variety of build environments.

Also, set +e is not entirely portable, i.e. some versions of Solaris (and even Dash) .. but I doubt that this is a concern for you.

edited Mar 4, 2010 at 3:35

answered Jul 2, 2009 at 15:40

user50049

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6 Comments

victor hugo Over a year ago

I removed the paths of your code and the root user because somebody might think you need to be su. Hope you don't mind ;)

user50049 Over a year ago

@victor hugo - Thanks. I edited this post a few times and failed to notice that I left the paths in tact :) I must be slightly brain dead today.

Toskan Over a year ago

i actually don't understand the part 2>&1 || true. I understand > /dev/null means the error gets redirected there but I neither understand the syntax nor the meaning of the other part. Can you maybe explain?

user50049 Over a year ago

@Toskan > /dev/null Redirects stdout to /dev/null. 2>&1 redirects stderr to stdout, effectively sending both stdout and stderr to the null device. || true ensures that the command exits with a zero status, even if it failed. It's like saying if this does not work, run /bin/true and return that value instead. It's a logical OR. E.g. [ -d /etc ] || echo "your system is broken" (if /etc is not a directory, echo something).

jpmc26 Over a year ago

Is redirecting the output to /dev/null optional? I have a bash script that calls a database client to drop some indexes, import a lot of data, and then restore the indexes. I'd like those indexes to be put back if the import fails, but I'd like to see the output and know the import failed, too. Can printing to stderr cause my script to exit after I called set -e, or can I just omit the redirect?

|

Adam Rosenfield · Accepted Answer · 2009-07-02 15:50:22Z

29

Disable the "exit immediately" option with set +e, run your command, then optionally re-enable it with set -e:

set +e
invoke-rc.d tomcat stop
set -e  # optional

See section 4.3.1 of the Bash manual for an explanation of the set builtin and all of its various options (of which there are many).

answered Jul 2, 2009 at 15:50

Adam Rosenfield

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Comments

score 4 · Accepted Answer · 2009-07-02 15:52:17Z

4

Use bash's set command to temporarily disable exit-on-nonzero behaviour.

set +e
invoke-rc.d tomcat stop
set -e

edited Jul 2, 2009 at 15:52

answered Jul 2, 2009 at 15:43

xyzzy

2 Comments

victor hugo Over a year ago

You should write a little explanation of your script. Just click 'edit'. BTW Welcome to SO

user50049 Over a year ago

set {args} is not always portable. However, if you do: set +e || { code to cope with a brain dead shell } Its just fine for anything worth its salt in POSIX conformity. Universally, its much easier (and much more portable) to just use true / false.

Vatine · Accepted Answer · 2009-07-02 16:08:14Z

1

If invoke-rc.d tomcat stop is the only thing you want to protect against failing, maybe invoke-rc.d tomcat stop || true may do it? That should never have a non-zero exit status.

answered Jul 2, 2009 at 16:08

Vatine

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Comments

Vaibhav · Accepted Answer · 2009-07-02 15:41:11Z

-4

Try redirecting the standard error to a file ...something like 2> myerror.

answered Jul 2, 2009 at 15:41

Vaibhav

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2 Comments

JorgeO Over a year ago

If seen something like command > /dev/null. Is it something like that? This will make the output of the command go to a file. But does also catch the error?

user50049 Over a year ago

This does not recover from the error, it merely hides the cause.

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