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Re: shopt can't set extglob in a sub-shell?


From: John Kearney
Subject: Re: shopt can't set extglob in a sub-shell?
Date: Sun, 26 Feb 2012 12:41:57 +0100
User-agent: Mozilla/5.0 (X11; Linux i686; rv:10.0) Gecko/20120129 Thunderbird/10.0

I updated that wiki page
Hopefully its clearer now.
http://mywiki.wooledge.org/glob#extglob


On 02/26/2012 12:06 PM, Dan Douglas wrote:
> On Saturday, February 25, 2012 09:42:29 PM Davide Baldini wrote:
> 
>> Description: A 'test.sh` script file composed exclusively of the
>> following text fails execution: #!/bin/bash ( shopt -s extglob 
>> echo !(x) ) giving the output: $ ./test.sh ./test.sh: line 4:
>> syntax error near unexpected token `(' ./test.sh: line 4: `
>> echo !(x)' Moving the shopt line above the sub-shell parenthesis
>> makes the script work.
>> 
>> The debian man pages give no explanation.
>> 
>> Thank you.
> 
> Non-eval workaround if you're desperate:
> 
> #!/usr/bin/env bash ( shopt -s extglob declare -a a='( !(x) )' echo
> "address@hidden" )
> 
> You may be aware extglob is special and affects parsing in other
> ways. Quoting Greg's wiki (http://mywiki.wooledge.org/glob):
> 
>> Likewise, you cannot put shopt -s extglob inside a function that
>> uses extended globs, because the function as a whole must be
>> parsed when it's defined; the shopt command won't take effect
>> until the function is called, at which point it's too late.
> 
> This appears to be a similar situation. Since parentheses are
> "metacharacters" they act strongly as word boundaries without a
> special exception for extglobs.
> 
> I just tested a bunch of permutations. I was a bit surprised to see
> this one fail:
> 
> f() if [[ $FUNCNAME != ${FUNCNAME[1]} ]]; then trap 'shopt -u
> extglob' RETURN shopt -s extglob f else f()( shopt -s extglob echo
> !(x) ) f fi
> 
> f
> 
> I was thinking there might be a general solution via the RETURN
> trap where you could just set "trace" on functions where you want
> it, but looks like even "redefinitions" break recursively, so
> you're stuck. Fortunately, there aren't a lot of good reasons to
> have extglob disabled to begin with (if any).




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