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Re: `if $(cmd);' is a positive when there's no output from cmd


From: Andreas Schwab
Subject: Re: `if $(cmd);' is a positive when there's no output from cmd
Date: Sun, 16 Apr 2006 14:46:35 +0200
User-agent: Gnus/5.110003 (No Gnus v0.3) Emacs/22.0.50 (gnu/linux)

Herculano Einloft <address@hidden> writes:

> Em (02:25:11), Andreas Schwab escreveu: 
>
>> 
>>> Hey all, 
>>> 
>>> $ if $(echo string >/dev/null); then echo true; fi 
>>> true 
>>> 
>>> This should be a syntax error 
>> 
>>No, it is a perfectly valid command, syntactically. That the command 
>>substitution expands to nothing has no significance any more once the 
>>command is parsed, just like shell meta characters resulting from 
>>expansions are taken literally. 
>> 
>>Andreas. 
>
> That's not true.. try: 
>
> $ echo $(echo \*) 
>
> or 
>
> $ a=*; echo "$a"; echo $a 
>
> for illustration. 

The '*' has no significance in the parser.

Andreas.

-- 
Andreas Schwab, SuSE Labs, address@hidden
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."




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