Two simple tricks for better shell script error handling

 If you decide to trap INT or TERM, it would be wise to properly kill your process with INT or TERM:

# if you're using bash, you can use $BASHPID in place of $$
for sig in INT TERM EXIT; do
    trap "rm -f \"\$TMPFILE\"; [[ $sig == EXIT ]] || kill -$sig $$" $sig
done

Not propagating signals in this manner is being a bad Unix citizen. Bash would have re-raised the SIGNAL, so you should too.

This guy has it figured out: http://www.cons.org/cracauer/sigint.html

I think most people are guily of this. I know I have been but I am forcing myself to do it now. I will definitely be using this! Thanks!

Thanks to Guns as well for his comment above. I've got some reading to do.

Very informational. Thanks a lot!

I've been using trap in Korn shell for years, works fine :-P

For simple scripts, -e may make life a little simpler, but be careful.

For instance, tar exits with 1 if a file changes during an archive create (-c), and it'll exit with 2 if a more serious error occurs.  So, if you use the -e approach, you'll have to do:

#!/bin/sh -e
...
set +e
tar cf /tmp/foo blah blah blah
if [ $? -eq 2 ]; then
    handle_error
else
    # we're ok
    :
fi
set -e
...

-

I have wrote the below script but it asking password for each server. what I will do so that it ask passwod one as it is asking more user name

Here is an example using a utility

http://www.perficient.com/Solutions-and-Services/Business-Integration-SOA/Reusable-Utility-Services

I have a simple shell script to run a .bin installer. My Shell script works fine if I run it as standalone. but I have to invoke it from ANT. When I invoke it from ANT, I am .bin installer runs fine, but with below message:

[exec] Extracting 0%....................................................................................................100%
     [exec] Unable to get term attrs
     [exec] Unable to get term attrs
 

Can anyone give me a hint what "Unable to get term attrs" and how to fix it?

thanks

is the trap working for script exiting on error too, or how can i make shure if the script exits (even for synatx error maybe) that a defined action is done?

Is there a way to protect a executing shell script from INT TERM. 
If there are critical jobs on the way. such as backup/restore. 
Thanks

Thank you so much for sharing your knowledge. It's work for me :)

Using #!/bin/sh -e is dangerous; what if I use "sh myscript.sh"? Then the -e flag is not set.

This is why using "set -e" is better, this way the flag *always*  gets set, no matter how you run the script.

Also look at -u, which causes the shell to exit on undefined variables.

 

when using set -e, dont forget to also set -o pipefail

man bash 

pipefail

If  set,  the  return value of a pipeline is the value of the last (rightmost) command to exit with a non-zero status, or zero if all commands in the pipeline exit successfully.  This option is disabled by default.

Hi,

I need to throw an exception from unix shell if during sftp, the file I am searching for is not found in sftp server location.

Thanks.