2 SC2233

Vidar Holen edited this page 2021-08-30 11:35:37 -07:00

Table of Contents

• Remove superfluous (..) around condition to avoid subshell overhead.
• Problematic code:
• Correct code:
• Rationale:
• Exceptions:
• Related resources:

Remove superfluous (..) around condition to avoid subshell overhead.

Problematic code:

if ([ "$x" -gt 0 ])
then true; fi

Correct code:

if [ "$x" -gt 0 ]
then true; fi

Rationale:

The shell syntax is if cmd, elif cmd, while cmd and until cmd without any parentheses. Instead, parentheses are an independent construct used to create subshells.

ShellCheck has noticed that you're wrapping (..) around one or more test commands. This is unnecessary, and the resulting fork adds quite a lot of overhead:

$ 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, so it can be safely ignored.

If you are considering doing it to stylistically match C-like languages, please note that this is not conventional and that you'd probably recommend someone use if (1 == 2) over if (system("[ 1 = 2 ]")) in C no matter which language they're used to.

Related resources:

• Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!

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