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Old 04-02-2008, 07:22 AM   #1
indiancosmonaut
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abnormal behavious in comparison check in 'if' condition.


Hi

Please look at the following code snipet.

Code:
xxx=0

if [ xxx -eq "0" ]
then
        echo "Im in if"
fi
It goes in the if condition! I fail to understand since xxx does not have a "$" in the condition check.
The shell is ksh and machine is AIX 5.3

Please provide some explanation. I would be very thankful.

Kind regards,

indiancosmonaut
 
Old 04-02-2008, 07:38 AM   #2
bigearsbilly
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well, obviously korn assumes $xxx in this case.
though I can't find any documentation.

if you use /usr/bin/test instead it fails.
 
Old 04-02-2008, 08:16 AM   #3
matthewg42
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I would imagine that when performing integer comparison (-eq and friends), any non-integer operands take the value of 0. Don't you get some warning message about it?
 
Old 04-02-2008, 08:36 AM   #4
bigearsbilly
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not so.
it must be a ksh feature!

Code:
$xxx=12
$ if [ xxx -eq 12  ]; then echo in if;fi 
in if

Code:
$ bash
bash-3.2$ xxx=12
bash-3.2$ if [ xxx -eq 12  ]; then echo in if;fi
bash: [: xxx: integer expression expected
bash-3.2$ if [ $xxx -eq 12  ]; then echo in if;fi
in if
/bin/sh
Code:
bash-3.2$ /bin/sh
$ xxx=12
$ if [ xxx -eq 12  ]; then echo in if;fi
$  if [ $xxx -eq 12  ]; then echo in if;fi
in if
 
Old 04-02-2008, 08:48 AM   #5
matthewg42
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that's far out
 
Old 04-02-2008, 11:05 AM   #6
indiancosmonaut
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Thanks gentlemen, for your analysis. I think you found a new thing in ksh. :-)

Kind regards,

indiancosmonaut
 
Old 04-02-2008, 11:24 AM   #7
bigearsbilly
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yes!
3 different results for 3 different, sort-of, compatible shells.

(on solaris anyway, /bin/sh is actually bash on linux)
 
Old 04-02-2008, 06:47 PM   #8
chrism01
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Hey BB, what do those 3 get if you use [[ ]] i.e. double brackets.?
I don't have access to all 3 shells, but was taught way back in a ksh course that [[ ]] is better.
 
Old 04-02-2008, 11:25 PM   #9
indiancosmonaut
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Hi,

In ksh it works with double square brackets also.

Code:
$ xxx=12
$ if [ xxx -eq 12 ]; then echo true!; fi
true!
$ if [[ xxx -eq 12 ]]; then echo true!; fi
true!
$
Is there a reason for preferring [[ ]] instead of []?

Kind regards,

indiancosmonaut
 
Old 04-02-2008, 11:34 PM   #10
konsolebox
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I think [[ is more of a macros than a command-line program that accepts parameters like [ or test.
I personally prefer [[ in bash than [ when it comes to arithmetic comparisons but use [ when it comes to string tests.
 
Old 04-03-2008, 12:10 AM   #11
chrism01
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double square brackets test is more robust: http://www.tldp.org/LDP/abs/html/tes...ml#DBLBRACKETS
 
  


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