(..)
around condition to avoid subshell
overhead.if ([ "$x" -gt 0 ])
then true; fi
if [ "$x" -gt 0 ]
then true; fi
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.
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.
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.