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Joachim Ansorg edited this page Nov 12, 2021 · 2 revisions

You probably wanted && here

Problematic code:

if  (( $1 != 0 || $1 != 3 ))
then
  echo "$1 is not 0 or 3"
fi

Correct code:

if  (( $1 != 0 && $1 != 3 ))
then
  echo "$1 is not 0 or 3"
fi

Rationale:

This is not a bash issue, but a simple, common logical mistake applicable to all languages.

(( $1 != 0 || $1 != 3 )) is always true:

  • If $1 = 0 then $1 != 3 is true, so the statement is true.
  • If $1 = 3 then $1 != 0 is true, so the statement is true.
  • If $1 = 42 then $1 != 0 is true, so the statement is true.

(( $1 != 0 && $1 != 3 )) is true only when $1 is not 0 and not 3:

  • If $1 = 0, then $1 != 3 is false, so the statement is false.
  • If $1 = 3, then $1 != 0 is false, so the statement is false.
  • If $1 = 42, then both $1 != 0 and $1 != 3 is true, so the statement is true.

This statement is identical to ! (( $1 == 0 || $1 == 3 )), which also works correctly.

Exceptions

None.

ShellCheck

Each individual ShellCheck warning has its own wiki page like SC1000. Use GitHub Wiki's "Pages" feature above to find a specific one, or see Checks.

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