How to exit if a command failed?

Question

I am a noob in shell-scripting. I want to print a message and exit my script if a command fails. I\'ve tried:

my_command && (echo \'my_command failed         


        

Answer 1

Try:

my_command || { echo 'my_command failed' ; exit 1; }

Four changes:

• Change && to ||
• Use { } in place of ( )
• Introduce ; after exit and
• spaces after { and before }

Since you want to print the message and exit only when the command fails ( exits with non-zero value) you need a || not an &&.

cmd1 && cmd2

will run cmd2 when cmd1 succeeds(exit value 0). Where as

cmd1 || cmd2

will run cmd2 when cmd1 fails(exit value non-zero).

Using ( ) makes the command inside them run in a sub-shell and calling a exit from there causes you to exit the sub-shell and not your original shell, hence execution continues in your original shell.

To overcome this use { }

The last two changes are required by bash.

Answer 2

You can also use, if you want to preserve exit error status, and have a readable file with one command per line:

my_command1 || exit $?
my_command2 || exit $?

This, however will not print any additional error message. But in some cases, the error will be printed by the failed command anyway.

Answer 3

I've hacked up the following idiom:

echo "Generating from IDL..."
idlj -fclient -td java/src echo.idl
if [ $? -ne 0 ]; then { echo "Failed, aborting." ; exit 1; } fi

echo "Compiling classes..."
javac *java
if [ $? -ne 0 ]; then { echo "Failed, aborting." ; exit 1; } fi

echo "Done."

Precede each command with an informative echo, and follow each command with that same
if [ $? -ne 0 ];... line. (Of course, you can edit that error message if you want to.)

Answer 4

Note also, each command's exit status is stored in the shell variable $?, which you can check immediately after running the command. A non-zero status indicates failure:

my_command
if [ $? -eq 0 ]
then
    echo "it worked"
else
    echo "it failed"
fi

Answer 5

The other answers have covered the direct question well, but you may also be interested in using set -e. With that, any command that fails (outside of specific contexts like if tests) will cause the script to abort. For certain scripts, it's very useful.

Answer 6

If you want that behavior for all commands in your script, just add

  set -e 
  set -o pipefail

at the beginning of the script. This pair of options tell the bash interpreter to exit whenever a command returns with a non-zero exit code.

This does not allow you to print an exit message, though.