GNU bug report logs - #20029
'yes' surprisingly slow

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From: Ole Tange <tange <at> gnu.org>
To: 20029 <at> debbugs.gnu.org
Subject: bug#20029: 'yes' surprisingly slow
Date: Sat, 7 Mar 2015 12:49:10 +0100

These two commands give the same output:

$ yes `echo {1..1000}` | head -c 2300M | md5sum
a0241f2247e9a37db60e7def3e4f7038  -

$ yes "`echo {1..1000}`" | head -c 2300M | md5sum
a0241f2247e9a37db60e7def3e4f7038  -

But the time to run is quite different:

$ time yes "`echo {1..1000}`" | head -c 2300M >/dev/null

real    0m0.897s
user    0m0.384s
sys     0m1.343s

$ time yes `echo {1..1000}` | head -c 2300M >/dev/null

real    0m11.352s
user    0m10.571s
sys     0m2.590s

WTF?!

I imagine 'yes' spends a lot of time collecting the 1000 args. But why
does it do that more than once?


/Ole

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