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From: Chris Down <chris@chrisdown.name>
Newsgroups: gnu.bash.bug
Subject: Re: performance bug of [[ $x ]]
Date: Sat, 7 Mar 2020 22:58:16 +0000
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Xref: csiph.com gnu.bash.bug:15999

Peng Yu writes:
>[[ $x ]] just tests whether the variable $x is of length 0 or not. So
>its performance should not depend on how long the variable is.

Who said it has anything to do with the [[ builtin's performance? A shell does 
a lot more than just running one command.

For this and the last issue you posted, you could quite trivially find out the 
answer yourself using `perf` or another profiler.