Re: [Xen-devel] [PATCH 1/1] tools/hotplug: Scan xenstore once when attaching shared images files

[Mike Latimer <mlatimer@xxxxxxxx>]

Hi again,

On Thursday, October 01, 2015 10:51:08 AM George Dunlap wrote:
> >
> > -      if [ "$d" = "$devmm" ]
> > +      if [[ "$devmm" == *"$d,"* ]]
> 
> Style nit: using [[ instead of [.  TBH I prefer [[, but it's probably
> better to be consistent with the rest of the file.

I was about to change this to something like:

  if [ "$devmm" != ${devmm/$d/} ]

but I'm a bit concerned about the potential size of the variables involved. If 
there are 500 devices with 5-7 characters per device, $devmm becomes a pretty 
large string. I'm not sure this bash substitution method is a great option. I 
also don't really want the hit of passing the variable to grep.

According to one post I found benchmarking various types of tests [1], the two 
fastest options are:

  [[ $b == *$a* ]]

  case $b in *$a):;;esac

I can implement a case statement, but that seems even less clean than the 
simple [[ ... ]] approach (since there is only one case we care about).

As this is a #!/bin/bash script, is [[ ... ]] okay to use, or would you prefer 
to use the case statement? (If you have any other ideas, I'm open to that as 
well.)

Thanks!
Mike

[1]http://stackoverflow.com/questions/229551/string-contains-in-bash  (search 
for 'fastest'

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