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; exit)

but it does not work. It keeps executing the instructions following this line in the script. I'm using Ubuntu and bash.

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.