Re: Use of '()' in a regexp

[Manuel Collado]

Well, it seems that RS='()' reads the whole file as a single record, but 
discards the last character, whatever is it.

$ printf 'foo\nbar' | awk -v RS='()' '{print "<"RT"><"$0">"}'
<><foo
ba>

Forcing to match at the end of the file doesn't consumes the last character.

$ printf 'foo\nbar' | awk -v RS='()$' '{print "<"RT"><"$0">"}'
<><foo
bar>

It looks like a bug.

Regards.


El 05/01/2021 a las 21:02, Ed Morton escribió:
> Hmm, it's not quite behaving the same as `RS='\n$'` as `RS='()'` doesn't
> populate `RT` with the terminating `\n` though it does consume it:
>
> $ printf 'foo\n' | awk -v RS='()' -v ORS='x\n' '{print "<"RT">"}1'
> <>x
> foox
>
> $ printf 'foo\n' | awk -v RS='\n$' -v ORS='x\n' '{print "<"RT">"}1'
> <
>  >x
> foox
>
>
> On 1/5/2021 12:38 PM, Ed Morton 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.


--
Manuel Collado - http://mcollado.z15.es