Automatic exit from Bash shell script on error

Question

I've been writing some shell script and I would find it useful if there was the ability to halt the execution of said shell script if any of the commands failed. See below for an example:

#!/bin/bash

cd some_dir

./configure --some-flags

make

make install

So in this case, if the script can't change to the indicated directory, then it would certainly not want to do a ./configure afterwards if it fails.

Now I'm well aware that I could have an if check for each command (which I think is a hopeless solution), but is there a global setting to make the script exit if one of the commands fails?

Answer 1

Use the set -e builtin:

#!/bin/bash
set -e
# Any subsequent(*) commands which fail will cause the shell script to exit immediately

Alternatively, you can pass -e on the command line:

bash -e my_script.sh

You can also disable this behavior with set +e.

You may also want to employ all or some of the the -e -u -x and -o pipefail options like so:

set -euxo pipefail

-e exits on error, -u errors on undefined variables, -x prints commands before execution, and -o (for option) pipefail exits on command pipe failures. Some gotchas and workarounds are documented well here.

(*) Note:

The shell does not exit if the command that fails is part of the command list immediately following a while or until keyword, part of the test following the if or elif reserved words, part of any command executed in a && or || list except the command following the final && or ||, any command in a pipeline but the last, or if the command's return value is being inverted with !

(from man bash)

Answer 2

To exit the script as soon as one of the commands failed, add this at the beginning:

set -e

This causes the script to exit immediately when some command that is not part of some test (like in a if [ ... ] condition or a && construct) exits with a non-zero exit code.

Answer 3

Use it in conjunction with pipefail.

set -e
set -o pipefail

-e (errexit): Abort the script at the first error, when a command exits with non-zero status (except in until or while loops, if-tests, and list constructs)

-o pipefail: Causes a pipeline to return the exit status of the last command in the pipe that returned a non-zero return value.

Chapter 33. Options

Answer 4

Here is how to do it:

#!/bin/sh

abort()
{
    echo >&2 '
***************
*** ABORTED ***
***************
'
    echo "An error occurred. Exiting..." >&2
    exit 1
}

trap 'abort' 0

set -e

# Add your script below....
# If an error occurs, the abort() function will be called.
#----------------------------------------------------------
# ===> Your script goes here
# Done!
trap : 0

echo >&2 '
************
*** DONE *** 
************
'

Answer 5

An alternative to the accepted answer that fits in the first line:

#!/bin/bash -e

cd some_dir  

./configure --some-flags  

make  

make install

Answer 6

One idiom is:

cd some_dir && ./configure --some-flags && make && make install

I realize that can get long, but for larger scripts you could break it into logical functions.

Answer 7

I think that what you are looking for is the trap command:

trap command signal [signal ...]

For more information, see this page.

Another option is to use the set -e command at the top of your script - it will make the script exit if any program / command returns a non true value.

Answer 8

One point missed in the existing answers is show how to inherit the error traps. The bash shell provides one such option for that using set

-E

If set, any trap on ERR is inherited by shell functions, command substitutions, and commands executed in a subshell environment. The ERR trap is normally not inherited in such cases.

---

Adam Rosenfield's answer recommendation to use set -e is right in certain cases but it has its own potential pitfalls. See GreyCat's BashFAQ - 105 - Why doesn't set -e (or set -o errexit, or trap ERR) do what I expected?

According to the manual, set -e exits

if a simple commandexits with a non-zero status. The shell does not exit if the command that fails is part of the command list immediately following a while or until keyword, part of the test in a if statement, part of an && or || list except the command following the final && or ||, any command in a pipeline but the last, or if the command's return value is being inverted via !".

which means, set -e does not work under the following simple cases (detailed explanations can be found on the wiki)

1. Using the arithmetic operator let or $((..)) ( bash 4.1 onwards) to increment a variable value as

   #!/usr/bin/env bash
   set -e
   i=0
   let i++                   # or ((i++)) on bash 4.1 or later
   echo "i is $i" 
   

2. If the offending command is not part of the last command executed via && or ||. For e.g. the below trap wouldn't fire when its expected to

   #!/usr/bin/env bash
   set -e
   test -d nosuchdir && echo no dir
   echo survived
   

3. When used incorrectly in an if statement as, the exit code of the if statement is the exit code of the last executed command. In the example below the last executed command was echo which wouldn't fire the trap, even though the test -d failed

   #!/usr/bin/env bash
   set -e
   f() { if test -d nosuchdir; then echo no dir; fi; }
   f 
   echo survived
   

4. When used with command-substitution, they are ignored, unless inherit_errexit is set with bash 4.4

   #!/usr/bin/env bash
   set -e
   foo=$(expr 1-1; true)
   echo survived
   

5. when you use commands that look like assignments but aren't, such as export, declare, typeset or local. Here the function call to f will not exit as local has swept the error code that was set previously.

   set -e
   f() { local var=$(somecommand that fails); }        
   g() { local var; var=$(somecommand that fails); }
   

6. When used in a pipeline, and the offending command is not part of the last command. For e.g. the below command would still go through. One options is to enable pipefail by returning the exit code of the first failed process:

   set -e
   somecommand that fails | cat -
   echo survived
   

The ideal recommendation is to not use set -e and implement an own version of error checking instead. More information on implementing custom error handling on one of my answers to Raise error in a Bash script