How to conditionally do something if a command succeeded or failed

Question

How can I do something like this in bash?

if "`command` returns any error";
then
    echo "Returned an error"
else
    echo "Proceed..."
fi

Answer 1

For small things that you want to happen if a shell command works, you can use the && construct:

rm -rf somedir && trace_output "Removed the directory"

Similarly for small things that you want to happen when a shell comand fails, you can use ||:

rm -rf somedir || exit_on_error "Failed to remove the directory"

It's probably unwise to do very much with these constructs, but they can on occasion make the flow of control a lot clearer.

Answer 2

That's exactly what bash's if statement does:

if command ; then
    echo "Command succeeded"
else
    echo "Command failed"
fi

Answer 3

Check the value of $?, which contains the result of executing the most recent command/function:

#!/bin/bash

echo "this will work"
RESULT=$?
if [ $RESULT -eq 0 ]; then
  echo success
else
  echo failed
fi

if [ $RESULT == 0 ]; then
  echo success 2
else
  echo failed 2
fi