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Use of colon

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# 1  
Old 09-09-2014
Use of colon
There was a sample code on forum I found sometime back:

Code:
$ f() { local foo=; : ${foo=unset}; declare -p foo; }; f
declare -- foo=""

$ f() { local foo; : ${foo=unset}; declare -p foo; }; f
declare -- foo="unset"

Can someone explain why was colon (:) is being used here. Whats its use?
Last edited by Don Cragun; 09-09-2014 at 05:45 PM.. Reason: Disable smilies in this posting.
# 2  
Old 09-09-2014
From the man page for the : command:
Code:
NAME
    colon - null utility
SYNOPSIS
    : [argument...]
DESCRIPTION
    This utility shall only expand command arguments. It is used when a command is needed, as in
    the then condition of an if command, but nothing is to be done by the command.

# 3  
Old 09-09-2014
Quote:
Originally Posted by Rameshck
Can someone explain why was colon (: ) is being used here.
Not really Smilie
Code:
$ help :
:: :
    Null command.
    
    No effect; the command does nothing.
    
    Exit Status:
    Always succeeds.
$

# 4  
Old 09-09-2014
Quote:
Originally Posted by junior-helper
Not really Smilie
Code:
$ help :
:: :
    Null command.
    
    No effect; the command does nothing.
    
    Exit Status:
    Always succeeds.
$

My thoughts too. It appears to do nothing special. I just began to wonder why they placed this option in shell. Thanks everyone.
# 5  
Old 09-09-2014
${foo=unset}, a conditional assignment, is run; the resulting value is discarded.
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