SC2255 – ShellCheck Wiki

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[ ] does not apply arithmetic evaluation. Evaluate with $((..)) for numbers, or use string comparator for strings.

Problematic code:

[ 2*3 -eq array[i] ]

Correct code:

[ $((2*3)) -eq $((array[i])) ]


When using [[ .. ]] with numerical comparators (-eq, -lt, etc), the value on either side will be evaluated as an arithmetic expression. This means that 2*3 will be evaluated to 6, and x will be evaluated to the contents of the variable $x.

When using [ .. ], this does not happen. 2*3 and x will both be considered invalid numbers. Instead, use e.g. $((2*3)) to evaluate the expression before passing it to [ .. ].

Alternatively, if the expression should be considered a string, quote the expression and use a string comparison operator like = and !=.



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