Re: [bug-gawk] gawk not working properly on the first line

[Davide Brini]

On Tue, 12 Aug 2014 01:55:42 +1000, Miriam English <address@hidden>
wrote:

> Yesterday I was trying to process a small table of tab-separated values 
> to select out 3 of the 6 columns and print them formatted. I used this 
> piece of awk along with some sed bits and pieces:
> awk '{FS="\t" ; print $3 "- " $2 "[" $5 "]"}'
> 
> Here is a sample table:
> Play 01       A Filbert is a Nut      Rick Raphael    Etext
>       Steve Mattingly Play 02         Ask a Foolish Question
> Robert Sheckley       Etext   Bellona Times Play 03   The
> Beast in the Void     Paul W. Fairman         Etext   James
> Rogers Play 04        The Burning Bridge      Poul William Anderson
>       Etext   Mark Nelson Play 05     From an Amber Block
>       Tom Curry       Etext   Lars Rolander
> 
> It is supposed to produce:
> Rick Raphael - A Filbert is a Nut [Steve Mattingly]
> Robert Sheckley - Ask a Foolish Question [Bellona Times]
> Paul W Fairman - The Beast in the Void [James Rogers]
> Poul William Anderson - The Burning Bridge [Mark Nelson]
> Tom Curry - From an Amber Block [Lars Rolander]
> 
> It worked perfectly on every line of the table except the first line.
> 
> A- 01[is]
> Robert Sheckley - Ask a Foolish Question [Bellona Times]
> Paul W. Fairman - The Beast in the Void [James Rogers]
> Poul William Anderson - The Burning Bridge [Mark Nelson]
> Tom Curry - From an Amber Block [Lars Rolander]
> 
> When I inserted a blank line before the first line it worked on that 
> line too, so it wasn't a problem with the line itself. It looks to me 
> like awk is not setting the field separator to TAB until after 
> processing the first line.
> 
> Is this a genuine bug or am I misusing awk somehow?


You are supposed to set FS before awk reads and tries to parse the line; in
this case, that means setting it in the BEGIN block or on the command line
with -v.

This is documented in the gawk manual, see

https://www.gnu.org/software/gawk/manual/gawk.html#Field-Splitting-Summary

the box titled "changing FS does not affect the fields".

-- 
D.