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Re: What shells fail to work if comparing with "" ?

From: Eric Blake
Subject: Re: What shells fail to work if comparing with "" ?
Date: Thu, 10 Feb 2011 14:13:30 -0700
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On 02/10/2011 12:40 PM, Ralf Wildenhues wrote:
> Hello David,
> * Dr. David Kirkby wrote on Thu, Feb 10, 2011 at 07:56:24PM CET:
>> I know its considered bad practice to check for an empty string with 
>> something like:
>> if [ "$STR" = "" ] ; then
>> but what shells do actually break with this, and under what conditions?
> It's not shells that break.  It's these kinds of issues:

Ralf pointed out a completely different point from the Solaris /bin/sh
syntax issue - that is, that in autoconf scripts, [ and ] are special to
m4, and require extra effort to use, so you are more portable using:

test "x$STR" = x

than you are using:

[ "x$STR" = x ]

so that m4 doesn't eat the [ and ].

Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library

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