[arch-projects] [devtools] [PATCH 2/2] makechrootpkg: Fix anti-pattern when checking for enabled features
lukeshu at lukeshu.com
Sat Sep 2 03:56:03 UTC 2017
On Fri, 01 Sep 2017 18:53:13 -0400,
Eli Schwartz wrote:
> Don't use error-prone logic e.g.
> foo=true; if $foo ...
Hey, I'm not to blame for this one :-)
> This invokes an extra process as opposed to a simple value comparison,
That's not quite true:
$ type true
true is a shell builtin
$ type false
false is a shell builtin
Bash won't actually make any syscalls when executing these commands in
a conditional. Apparently the code paths within Bash are slightly
faster for `[[ $v = true ]]` than for `$v`, but that's negligible
compared to if it actually had to invoke an extra process as you said.
Time for 1 million iterations:
"v=true; if $v; then ..." | 7.1 sec
"v=true; if [[ $v = true ]]; then ..." | 6.5 sec
"v=/bin/true; if $v; then ..." | > 5 minutes (I got bored and killed it)
> in the process of completely failing to act as expected when the
> variable is unset because of unrelated bugs.
And that's the real reason that this change should be applied. :-)
~ Luke Shumaker
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