SC2234 – ShellCheck Wiki

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Remove superfluous `(..)` around test command to avoid subshell overhead.

Problematic code:

([ "$x" -gt 0 ]) && foo

Correct code:

[ "$x" -gt 0 ] && foo

Rationale:

You are wrapping a single test command in (..), creating an unnecessary subshell. This serves no purpose, but is significantly slower:

$ i=0; time while ( [ "$i" -lt 10000 ] ); do i=$((i+1)); done
real    0m6.998s
user    0m3.453s
sys     0m3.464s

$ i=0; time while [ "$i" -lt 10000 ]; do i=$((i+1)); done
real    0m0.055s
user    0m0.054s
sys     0m0.001s

Just delete the surrounding (..) since they serve no purpose and only slows the script down.

Exceptions:

This issue only affects performance, not correctness, and can be ignored for stylistic reasons.

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