CODEWITHSUNDEEP
linuxbashunixshell
Jin Kim
Jin Kim

Reputation: 17722

Aborting a shell script if any command returns a non-zero value

I have a Bash shell script that invokes a number of commands.

I would like to have the shell script automatically exit with a return value of 1 if any of the commands return a non-zero value.

Is this possible without explicitly checking the result of each command?

For example,

dosomething1
if [[ $? -ne 0 ]]; then
    exit 1
fi

dosomething2
if [[ $? -ne 0 ]]; then
    exit 1
fi

Upvotes: 626

Views: 267022

Answers (10)

ShaulF
ShaulF

Reputation: 890

On error, the below script will print a RED error message with the failed command and then will exit.
Put this at the top of your bash script:

# BASH error handling:
#   exit on command failure
set -e
#   keep track of the last executed command
trap 'LAST_COMMAND=$CURRENT_COMMAND; CURRENT_COMMAND=$BASH_COMMAND' DEBUG
#   on error: print the failed command
trap 'ERROR_CODE=$?; FAILED_COMMAND=$LAST_COMMAND; tput setaf 1; echo "ERROR: command \"$FAILED_COMMAND\" failed with exit code $ERROR_CODE"; tput sgr0;' ERR INT TERM

Upvotes: 10

Ville Laurikari
Ville Laurikari

Reputation: 29248

Add this to the beginning of the script:

set -e

This will cause the shell to exit immediately if a simple command exits with a nonzero exit value. A simple command is any command not part of an if, while, or until test, or part of an && or || list.

See the bash manual on the "set" internal command for more details.

It's really annoying to have a script stubbornly continue when something fails in the middle and breaks assumptions for the rest of the script. I personally start almost all portable shell scripts with set -e.

If I'm working with bash specifically, I'll start with

set -Eeuo pipefail

This covers more error handling in a similar fashion. I consider these as sane defaults for new bash programs. Refer to the bash manual for more information on what these options do.

Upvotes: 996

Malina
Malina

Reputation: 9

I am just throwing in another one for reference since there was an additional question to Mark Edgars input and here is an additional example and touches on the topic overall:

[[ `cmd` ]] && echo success_else_silence

Which is the same as cmd || exit errcode as someone showed.

For example, I want to make sure a partition is unmounted if mounted:

[[ `mount | grep /dev/sda1` ]] && umount /dev/sda1

Upvotes: -3

leonbloy
leonbloy

Reputation: 75896

To add to the accepted answer:

Bear in mind that set -e sometimes is not enough, specially if you have pipes.

For example, suppose you have this script

#!/bin/bash
set -e 
./configure  > configure.log
make

... which works as expected: an error in configure aborts the execution.

Tomorrow you make a seemingly trivial change:

#!/bin/bash
set -e 
./configure  | tee configure.log
make

... and now it does not work. This is explained here, and a workaround (Bash only) is provided:

#!/bin/bash
set -e 
set -o pipefail

./configure  | tee configure.log
make

Upvotes: 279

Baligh Uddin
Baligh Uddin

Reputation: 79

#!/bin/bash -e

should suffice.

Upvotes: 7

user98989
user98989

Reputation:

Run it with -e or set -e at the top.

Also look at set -u.

Upvotes: 15

Mark Edgar
Mark Edgar

Reputation: 4797

The $? variable is rarely needed. The pseudo-idiom command; if [ $? -eq 0 ]; then X; fi should always be written as if command; then X; fi.

The cases where $? is required is when it needs to be checked against multiple values:

command
case $? in
  (0) X;;
  (1) Y;;
  (2) Z;;
esac

or when $? needs to be reused or otherwise manipulated:

if command; then
  echo "command successful" >&2
else
  ret=$?
  echo "command failed with exit code $ret" >&2
  exit $ret
fi

Upvotes: 18

Nails N.
Nails N.

Reputation: 561

If you have cleanup you need to do on exit, you can also use 'trap' with the pseudo-signal ERR. This works the same way as trapping INT or any other signal; bash throws ERR if any command exits with a nonzero value:

# Create the trap with   
#    trap COMMAND SIGNAME [SIGNAME2 SIGNAME3...]
trap "rm -f /tmp/$MYTMPFILE; exit 1" ERR INT TERM
command1
command2
command3
# Partially turn off the trap.
trap - ERR
# Now a control-C will still cause cleanup, but
# a nonzero exit code won't:
ps aux | grep blahblahblah

Or, especially if you're using "set -e", you could trap EXIT; your trap will then be executed when the script exits for any reason, including a normal end, interrupts, an exit caused by the -e option, etc.

Upvotes: 30

Zan Lynx
Zan Lynx

Reputation: 54325

The if statements in your example are unnecessary. Just do it like this:

dosomething1 || exit 1

If you take Ville Laurikari's advice and use set -e then for some commands you may need to use this:

dosomething || true

The || true will make the command pipeline have a true return value even if the command fails so the the -e option will not kill the script.

Upvotes: 105

gabor
gabor

Reputation: 1030

An expression like

dosomething1 && dosomething2 && dosomething3

will stop processing when one of the commands returns with a non-zero value. For example, the following command will never print "done":

cat nosuchfile && echo "done"
echo $?
1

Upvotes: 4

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