Re: bug in latest awk release

[Mirco Meniconi]

Dear Stepan,

Thank you for your very clear explanation,
anyway let me tell you that the command  
#~/gawk-3.1.5/gawk 'FS="\t" {print $1}' f.txt 
works well using the SGI compiled verison of awk (where well means how I would
have expected before your esplanation) .... maybe this is due to the
not-complete compatibility between the standard Awk and the Gnu-Awk ... ???

Best Regards
 
--- Stepan Kasal <address@hidden> ha scritto: 

> Hello,
> 
> On Tue, Sep 13, 2005 at 10:11:40AM +0200, Mirco Meniconi wrote:
> > ~/gawk-3.1.5/gawk -v FS="\t" '{print $1}' f.txt
> 
> this is correct command.  Alternatively, you might use:
> 
> gawk 'BEGIN{FS="\t"} {print $1}' f.txt
> 
> or
> 
> gawk '{print $1}' FS="<tab>"  f.txt
> 
> (The <tab> would have to be real tab character.)
> 
> But the following awk program is buggy:
> 
> > #~/gawk-3.1.5/gawk 'FS="\t" {print $1}' f.txt
> 
> Before we get to this program, let me remind that the awk program
> consists of PATTERN ACTION pairs.
> 
> So you can use
>       $2 != "" {print}
> to select lines with non-empty second field.
> 
> So in your example:
>       FS="\t" {print $1}
> the "condition" is the assignment to FS.  It is always true, so all
> lines are printed.  But the FS is changes only when the condition is
> evaluated.  This means that the first line is split according to
> the default FS.  Then the FS is changed, so the second line will be
> split using tab as the FS.  But the first line is already split, and
> $1 was already computed.
> 
> Perhaps reading the gawk manual ("info gawk") or a fine book about
> awk might help you.  Then your first attempt would be to place the
> assignment to BEGIN.
> 
> With regards,
>       Stepan Kasal
> 




        

        
                
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