performance bug of [[ $x ]]

From	Peng Yu <pengyu.ut@gmail.com>
Newsgroups	gnu.bash.bug
Subject	performance bug of [[ $x ]]
Date	2020-03-07 16:48 -0600
Message-ID	<mailman.2266.1583621332.2412.bug-bash@gnu.org> (permalink)
References	<CABrM6w=ignEwgynRTYYbBLUNs=KVhE8WCf9h=kkgHj00QNoqmw@mail.gmail.com>

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[[ $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.

But the following test case shows that the run time does depend on the
length of the variable.

Should it be considered as a performance bug of bash?

$ x=$(printf '%.sx' {1..1000000})
$ time [[ $x ]]

real	0m0.004s
user	0m0.003s
sys	0m0.000s
$ x=$(printf '%.sx' {1..10000000})
$ time [[ $x ]]

real	0m0.043s
user	0m0.039s
sys	0m0.004s

-- 
Regards,
Peng

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performance bug of [[ $x ]] Peng Yu <pengyu.ut@gmail.com> - 2020-03-07 16:48 -0600

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