Re: [bug-gawk] gawk 4.1.3 gensub() warning

[Stephane Chazelas]

2015-09-03 06:34:42 -0600, address@hidden:
> Ed Morton <address@hidden> wrote:
> 
> > I'm seeing this new warning in gawk 4.1.3 executing existing scripts:
> >
> > $ echo 'a' | gawk '{print gensub(/a/,"b","")}'
> > gawk: cmd. line:1: (FILENAME=- FNR=1) warning: gensub: third argument `' 
> > treated 
> > as 1
> > b
> >
> > This will impact a ton of scripts, like if sed suddenly started issuing 
> > warnings 
> > if you wrote `s/foo/bar/` instead of `s/foo/bar/1`. Is it here to stay?
> >
> >      Ed.
> 
> The warning is indeed here to stay. Use of "" is wrong; you should
> supply a numeric 1 there.  Fix your scripts.
[...]

I can confirm that the use of gensub(/x/, repl, "") is
widespread.

On unix.stackexchange.com for instance, at a quick glance, a
large proportion of the answers involving a non-"g" gensub
(https://unix.stackexchange.com/search?q=gensub) have "" instead
of 1.

A few examples:

https://unix.stackexchange.com/questions/170606/extracting-trace-information-using-gawk/212892#212892
https://unix.stackexchange.com/questions/216544/how-to-print-a-line-if-that-line-or-the-next-line-do-not-contain-a-particular-st/216581#216581
https://unix.stackexchange.com/questions/72425/awk-gensub-function/72432#72432
https://unix.stackexchange.com/questions/23174/increment-number-in-bash-variable-string/23176#23176
https://unix.stackexchange.com/questions/183883/how-to-highlight-given-string-in-given-place/188450#188450
https://unix.stackexchange.com/questions/182400/print-ip-address-with-interface-name/182471#182471
https://unix.stackexchange.com/questions/205540/append-something-to-each-list-in-a-file/205584#205584

A search on usenet comp.lang.awk
(https://groups.google.com/forum/#!searchin/comp.lang.awk/gensub)
seems to bring a few as well

Though the behaviour for "" is undocumented, that's what easily
comes to mind if you translate a sed/ed s/x/y/ command to awk.

So I can easily imagine this change causing some annoyance.

-- 
Stephane