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Can anyone tell me what's wrong here...

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Top Forums Shell Programming and Scripting Can anyone tell me what's wrong here...
# 15  
Old 03-20-2013
@MadeInGermany: You first result does not work? I get:

Code:
$ echo 0 | awk '{B=$1; print (B?"YES":"NO")}'
NO
$ echo 0 | awk '{B=$1; print (B""?"YES":"NO")}'
YES
$ echo 0 | awk '{B=$1; print (B!=""?"YES":"NO")}'
YES
$ echo 0 | awk '{B=$1""; print B?"YES":"NO"}'
YES

# 16  
Old 03-20-2013
Depends on the awk version.
Solaris /usr/xpg4/bin/awk says NO, nawk and gawk say YES:
Code:
echo 0 | /usr/xpg4/bin/awk '{B=$1; print (B!=""?"YES":"NO")}'
NO

This User Gave Thanks to MadeInGermany For This Post:
Scrutinizer
# 17  
Old 03-20-2013
I found the following regarding the B!="" case:
Quote:
Comparisons (with the '<' , "<=" , "!=" , "==" , '>' , and ">=" operators) shall be made numerically if both operands are numeric, if one is numeric and the other has a string value that is a numeric string, or if one is numeric and the other has the uninitialized value. Otherwise, operands shall be converted to strings as required and a string comparison shall be made using the locale-specific collation sequence. The value of the comparison expression shall be 1 if the relation is true, or 0 if the relation is false.
Expressions in awk

--edit--

I narrowed it down to:

Code:
$ /usr/xpg4/bin/awk 'BEGIN{print (0==""?"YES":"NO")}'
YES
$ /usr/xpg4/bin/awk 'BEGIN{print ("0"==""?"YES":"NO")}'
NO
$ nawk 'BEGIN{print (0==""?"YES":"NO")}'
NO
$ nawk 'BEGIN{print ("0"==""?"YES":"NO")}'
NO

$ gawk 'BEGIN{print (0==""?"YES":"NO")}'
NO
$ gawk 'BEGIN{print ("0"==""?"YES":"NO")}'
NO
$ gawk4 'BEGIN{print (0==""?"YES":"NO")}'
NO
$ gawk4 'BEGIN{print ("0"==""?"YES":"NO")}'
NO
$ bwk 'BEGIN{print (0==""?"YES":"NO")}'
NO
$ bwk 'BEGIN{print ("0"==""?"YES":"NO")}'
NO
$ mawk 'BEGIN{print (0==""?"YES":"NO")}'
NO
$ mawk 'BEGIN{print ("0"==""?"YES":"NO")}'
NO

Last edited by Scrutinizer; 03-20-2013 at 10:04 AM..
This User Gave Thanks to Scrutinizer For This Post:
MadeInGermany
# 18  
Old 03-20-2013
So what applies here?
I think:
Quote:
Otherwise, operands shall be converted to strings as required and a string comparison shall be made using the locale-specific collation sequence.
In this case "0"!="" -> YES, and there is a bug in Solaris /usr/xpg4/bin/awk.
Do you agree?
# 19  
Old 03-20-2013
It would not be the first bug is solaris awk... ( I dont remember what but I suffered from one two year ago...) but this is more of a nuisance because I tend to use /usr/xpg4/bin/awk for it seemed less buggy...
thanks to both of you for such a in deep investigation!
# 20  
Old 03-20-2013
Quote:
Originally Posted by MadeInGermany
So what applies here?
I think:

In this case "0"!="" -> YES, and there is a bug in Solaris /usr/xpg4/bin/awk.
Do you agree?
I think it isn't an actual bug, but rather a matter of strict conformance to historical standards..

/usr/xpg4/bin/awk conforms to the older POSIX.2/POSIX.2a/XPG4 standards.

I found this piece in the latest POSIX.1-2008:
Quote:
The description for comparisons in the ISO POSIX-2:1993 standard did not properly describe historical practice because of the way numeric strings are compared as numbers. The current rules cause the following code:

Code:
if (0 == "000")
    print "strange, but true"
else
    print "not true"

to do a numeric comparison, causing the if to succeed. It should be intuitively obvious that this is incorrect behavior, and indeed, no historical implementation of awk actually behaves this way.

To fix this problem, the definition of numeric string was enhanced to include only those values obtained from specific circumstances (mostly external sources) where it is not possible to determine unambiguously whether the value is intended to be a string or a numeric.
Expressions in awk
Last edited by Scrutinizer; 03-20-2013 at 07:17 PM..
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