How can I do an if conditional for a failure of a bash command?

Question

I'd like to have a very simple condition that will only execute if the command fails.

In this example it's a conditional based on the SUCCESS of the command.

if command ; then
    echo "Command succeeded"
fi

I'd like the opposite - how can I do this? Is there a elagant way besides doing a comparison on $?

I do not want to use the || or operator - it does semantically convey (in my opinion) the desired functionality. In the case of command || echo "command failed".

Related: [What are the shell's control and redirection operators?](https://unix.stackexchange.com/a/159514/65304) — steeldriver, Oct 09 '19 at 13:39
You may find examples in this thread useful: https://askubuntu.com/questions/512770/what-is-use-of-command-command
`command -v "$1" >/dev/null 2>&1` — t7e, Jun 25 '22 at 14:47

Stephen Kitt · Accepted Answer · 2019-10-09T13:56:01.333

22

Negate the command’s exit status:

if ! command ; then
    echo "Command failed"
fi

edited Oct 09 '19 at 13:56

answered Oct 09 '19 at 13:37

Stephen Kitt

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score 3 · Answer 2 · answered Oct 09 '19 at 14:42

3

An alternative to @StephenKitt's correct answer: use the : "no-op" command in the "then" block and the else block:

if command; then :; else
    echo "command failed"
fi

Full disclosure: I would not use this method myself.

answered Oct 09 '19 at 14:42

glenn jackman

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1

That's what you had to use in the Bourne shell which didn't have the `!` keyword (added in ksh88e and bash in 1.11 or before) – Stéphane Chazelas Oct 09 '19 at 15:53

How can I do an if conditional for a failure of a bash command?

2 Answers2