Bash – How to exit a shell script if one part of it fails

You can use bash trap ERR to make your script quit if any command returns status greater than zero and execute your function on exiting.

Something like:

myfunc() {
  echo 'Error raised. Exiting!'
}

trap 'myfunc' ERR

# file does not exist, causing error
ls asd
echo 123

Note that bash trap ERR does implicit set -o errexit or set -e and is not POSIX.

And the ERR trap is not executed if the failed command is part of the command list immediately following until or while keyword, part of the test following the if or elif reserved words, part of a command executed in && or || list, or if the command’s return status is being inverted using !.

Replace:

done

with:

done || exit 1

This will cause the code to exit if the for loop exits with a non-zero exit code.

As a point of trivia, the 1 in exit 1 is not needed. A plain exit command would exit with the exit status of the last executed command which would be false (code=1) if the download fails. If the download succeeds, the exit code of the loop is the exit code of the echo command. echo normally exits with code=0, signally success. In that case, the || does not trigger and the exit command is not executed.

Lastly, note that set -o errexit can be full of surprises. For a discussion of its pros and cons, see Greg's FAQ #105.

Documentation

From man bash:

for (( expr1 ; expr2 ; expr3 )) ; do list ; done
First, the arithmetic expression expr1 is evaluated according the rules described below under ARITHMETIC EVALUATION. The arithmetic expression expr2 is then evaluated repeatedly until it evaluates to zero. Each time expr2 evaluates to a non-zero value, list is executed and the arithmetic expression expr3 is evaluated. If any expression is omitted, it behaves as if it evaluates to 1. The return value is the exit status of the last command in list that is executed, or false if any of the expressions is invalid. [Emphasis added]