substitution groups and patterns i replace string (Emacs' \\1 etc.)

substitution groups and patterns i replace string (Emacs' \\1 etc.)

[Emanuel Berg]

When I do substitution, can I do groups and patterns
like in Emacs with \\1, \\2 to reference the
particular matches, and thus construct the replace
string out of them any way I like?
        
Or, can I feed the match to a function which I define
myself which returns the replace string? I think I can
bash it together tho it won't be as elegant...

I particular, I'm doing text-to-HTML conversion so
I want to search for http://... the URLs in the text.
To search for them is easy enough but how do I use the
result (the match string) to construct the
replacement, i.e. <a href="\\1"> ... </a> if, again,
the Emacs notation is used to illustrate?

-- 
underground experts united
http://user.it.uu.se/~embe8573

Re: substitution groups and patterns i replace string (Emacs' \\1 etc.)

[Peter Stephenson]

On Thu, 3 Mar 2016 02:08:22 +0100
Emanuel Berg <embe8573@student.uu.se> wrote:
> When I do substitution, can I do groups and patterns
> like in Emacs with \\1, \\2 to reference the
> particular matches, and thus construct the replace
> string out of them any way I like?

You do it with $match, and if you need to refer to positions in the
original string, $mbegin and $mend.  See the description of the (#b)
pattern in the zshexpn manual page.

local -a match mbegin mend

if [[ $url = (#b)http://(*) ]]; then
  print $match[1]
fi

Works with other forms of pattern matching.

pws

Re: substitution groups and patterns i replace string (Emacs' \\1 etc.)

[Emanuel Berg]

Peter Stephenson <p.stephenson@samsung.com> writes:

>> When I do substitution, can I do groups and
>> patterns like in Emacs with \\1, \\2 to reference
>> the particular matches, and thus construct the
>> replace string out of them any way I like?
>
> You do it with $match, and if you need to refer to
> positions in the original string, $mbegin and $mend.
> See the description of the (#b) pattern in the
> zshexpn manual page.

I have now checked out the zshexpn(1) man page but the
examples there are very complicated!

> local -a match mbegin mend
>
> if [[ $url = (#b)http://(*) ]]; then print $match[1]
> fi

Thanks, but this syntax is very bulky compared to
Emacs and sed. How it is supposed to be used for
a stream of text or a variable with several hit
instances? I'm not saying it can't be done only
compared to Emacs (and sed) it seems
unnecessarily complicated.

Perhaps Emacs/sed syntax in this case is something
that can be added to zsh?

-- 
underground experts united
http://user.it.uu.se/~embe8573

Re: substitution groups and patterns i replace string (Emacs' \\1 etc.)

[Mikael Magnusson]

On Sun, Mar 6, 2016 at 6:57 AM, Emanuel Berg <embe8573@student.uu.se> wrote:
> Peter Stephenson <p.stephenson@samsung.com> writes:
>
>>> When I do substitution, can I do groups and
>>> patterns like in Emacs with \\1, \\2 to reference
>>> the particular matches, and thus construct the
>>> replace string out of them any way I like?
>>
>> You do it with $match, and if you need to refer to
>> positions in the original string, $mbegin and $mend.
>> See the description of the (#b) pattern in the
>> zshexpn manual page.
>
> I have now checked out the zshexpn(1) man page but the
> examples there are very complicated!
>
>> local -a match mbegin mend
>>
>> if [[ $url = (#b)http://(*) ]]; then print $match[1]
>> fi

% a="> Thanks, but this syntax is very bulky compared to
> Emacs and sed. How it is supposed to be used for
> a stream of text or a variable with several hit
> instances? I'm not saying it can't be done only
> compared to Emacs (and sed) it seems
> unnecessarily complicated."

% echo ${a//(#b)([aoeui])/${(U)match[1]}}
> ThAnks, bUt thIs syntAx Is vEry bUlky cOmpArEd tO
> EmAcs And sEd. HOw It Is sUppOsEd tO bE UsEd fOr
> A strEAm Of tExt Or A vArIAblE wIth sEvErAl hIt
> InstAncEs? I'm nOt sAyIng It cAn't bE dOnE Only
> cOmpArEd tO EmAcs (And sEd) It sEEms
> UnnEcEssArIly cOmplIcAtEd.


-- 
Mikael Magnusson

Re: substitution groups and patterns i replace string (Emacs' \\1 etc.)

[Bart Schaefer]

On Mar 6,  8:15am, Mikael Magnusson wrote:
}
} % echo ${a//(#b)([aoeui])/${(U)match[1]}}

It's actually quite simple to make $1, $2, ... refer to the values in
the $match array during ${v//p/r} substitutions.  This would make the
syntax look very perl-ish, but would mean you can't combine backrefs
with expansions of the normal positional parameters.

Anyone interested?  Discuss?

Incidentally, for a fun time consider replacing ${(U)match[1]} with
${(P)match[1]} in that substitution of Mikael's.