Re: Use of '()' in a regexp

[Ed Morton]

In case that's not an adequate example, what I mean is, will this:

$ printf 'foo\nbar\n' | awk -v RS='()' -v ORS='X' '1' file

then produce the same output as this:

$ printf 'foo\nbar\n' | awk -v RS='^$' '{gsub(/()/,"X")}1'
XfXoXoX
XbXaXrX
X

or not and, if not, why is it different?

I just noticed that this seems to handle `/()/` differently from either 
of the current cases again:

$ printf 'foo\nbar\n' | awk '{nf=split($0,flds,/()/,seps); print nf; for 
(i=0; i<=nf; i++) printf "%s%s", flds[i], "<"seps[i]">" ; print ""}'
1
<>foo<>
1
<>bar<>

Regards,

    Ed.

On 1/6/2021 2:54 PM, Ed Morton wrote:
> Great! Will that treat `()` when used in an RS:
>
>     awk -v RS='()' -v ORS='x' '1'
>
> the same as it's treated in a regexp in other contexts such as with 
> gsub():
>
>     awk -v ORS= '{gsub(/()/,"x")} 1'
>
> or does it mean something different when used in an RS?
>
>     Ed.
>
> On 1/6/2021 1:33 PM, arnold@skeeve.com wrote:
> > Hi. Re this:
> >
> > Ed Morton<mortoneccc@comcast.net>  wrote:
> >
> > > Someone just pointed this out to me (gawk 5.1.0):
> > >
> > > $ printf 'foo\n' | awk '{gsub(/()/,"x")} 1'
> > > xfxoxox
> > >
> > > $ printf 'foo\n' | awk -v RS='()' -v ORS='x\n' '1'
> > > foox
> > >
> > > Obviously that's a pretty ridiculous regexp but it still has me
> > > wondering - why does `gsub()` treat the regexp `()` as matching a null
> > > string around every character while `RS` treats it as if I'd asked it to
> > > match the `\n` at the end of the input:
> > >
> > > $ printf 'foo\n' | awk -v RS='\n$' -v ORS='x\n' '1'
> > > foox
> > >
> > > I could just file this under "don't write stupid regexps" but I was
> > > wondering if there's a more concrete, satisfying explanation of the
> > > behavior.
> > >
> > >       Ed.
> > It's a bug. This appears to be the fix. It doesn't break the
> > test suite, either.
> >
> > Thanks for the report!
> >
> > Arnold
> > -----------------------------------------
> > diff --git a/io.c b/io.c
> > index 2714398e..0af8ab1e 100644
> > --- a/io.c
> > +++ b/io.c
> > @@ -3702,7 +3702,7 @@ again:
> >                  * If still room in buffer, skip over null match
> >                  * and restart search. Otherwise, return.
> >                  */
> > -               if (bp + iop->scanoff < iop->dataend) {
> > +               if (bp + iop->scanoff <= iop->dataend) {
> >                         bp += iop->scanoff;
> >                         goto again;
> >                 }