2 SC2310

Christian Nassif-Haynes edited this page 2021-10-17 03:15:35 +11:00

Table of Contents

• This function is invoked in an 'if' condition so set -e will be disabled. Invoke separately if failures should cause the script to exit.
• Problematic code:
• Correct code:
• Rationale:
• Exceptions:
• Related resources:

This function is invoked in an 'if' condition so set -e will be disabled. Invoke separately if failures should cause the script to exit.

(This warning is optional and must be explicitly enabled)

Problematic code:

#!/bin/sh
#shellcheck enable=check-set-e-suppressed

set -e

backup() {
  cp *.txt /backup
  rm *.txt            # Runs even if copy fails!
}

if backup
then
    echo "Backup successful"
fi

Correct code:

#!/bin/sh
#shellcheck enable=check-set-e-suppressed

set -e

backup() {
  cp *.txt /backup
  rm *.txt
}

backup
echo "Backup successful"

Rationale:

ShellCheck found a function used as a condition in a script where set -e is enabled. This means that the function will run without set -e, and will power through any errors.

This applies to if, while, and until statements, commands negated with !, as well as the left-hand side of || and &&. It does not matter how deeply the command is nested in such a structure.

In the problematic example, the intent was that an error like cp: error writing '/backup/important.txt': No space left on device would cause the script to abort. Instead, since the function is invoked in an if statement, the script will proceed to delete all the files even though it failed to back them up.

The fix is to call it outside of an if statement. There is no point in checking whether the command succeeded, since the script would abort if it didn't. You may also want to consider replacing set -e with explicit || exit after every relevant command to avoid such surprises.

Exceptions:

If you don't care that the function runs without set -e, you can disable this warning.

Related resources:

• BashFaq #105: Why doesn't set -e (or set -o errexit, or trap ERR) do what I expected?

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