grouping in awk
in [Shell]
|
Prev: Shell script to do like winmerge.... :)
Next: Opening a File via Pipes, Redirection and direct access and its effect on Command
From: Otavio Exel on 14 Apr 2008 15:14 Dear Group, it is a shame that I can't find the answer to such a simple question! I read in the awk man pages that awk supports grouping; but how do I use the parts of the mach? let's say I'd like to replace "<a,b>" with "<b,a>"; in sed I'd do: s/<\(.*\),\(.*\)>/<\2,\1>/ in awk I expected to do sub( "<(.*),(.*)>", "<\2,\1>" ) ....but (guess?) it didn't work! any clues? []s and TIA! -- Otavio Exel /<\oo/>\ oexel(a)economatica.com.br
From: Wayne on 14 Apr 2008 15:49 Otavio Exel wrote: > Dear Group, > > it is a shame that I can't find the answer to such a simple question! > > I read in the awk man pages that awk supports grouping; > but how do I use the parts of the mach? > > let's say I'd like to replace "<a,b>" with "<b,a>"; > > in sed I'd do: > > s/<\(.*\),\(.*\)>/<\2,\1>/ > > in awk I expected to do > > sub( "<(.*),(.*)>", "<\2,\1>" ) > > ...but (guess?) it didn't work! > > any clues? > > []s and TIA! > That is a feature of Gnu awk (gawk): $ echo abc |awk '{result=gensub(/a(b)c/, "x\\1y","g"); print result;}' xby -Wayne
From: Wayne on 14 Apr 2008 16:09 Otavio Exel wrote: > Dear Group, > > it is a shame that I can't find the answer to such a simple question! > > I read in the awk man pages that awk supports grouping; > but how do I use the parts of the mach? > > let's say I'd like to replace "<a,b>" with "<b,a>"; > > in sed I'd do: > > s/<\(.*\),\(.*\)>/<\2,\1>/ > > in awk I expected to do > > sub( "<(.*),(.*)>", "<\2,\1>" ) > > ...but (guess?) it didn't work! > > any clues? > > []s and TIA! > That is a feature of Gnu awk (gawk): $ echo '<a,b>' |awk ' {result=gensub(/<(.*),(.*)>/, "<\\2,\\1>",1); $0=result}1' <b,a> -Wayne
From: Otavio Exel on 17 Apr 2008 10:18 > Otavio Exel wrote: > > > > I read in the awk man pages that awk supports grouping; > > but how do I use the parts of the mach? Wayne <nospam(a)all4me.invalid> wrote: > > That is a feature of Gnu awk (gawk): Wayne, I'd rather not use "special" feature; I'll find a way using sed. but a very interesting question remains: - why does awk support grouping than? - IOW: what can you do with the "groups"? []s, -- Otavio Exel /<\oo/>\ oexel(a)economatica.com.br
From: Ed Morton on 17 Apr 2008 12:00
On 4/17/2008 9:18 AM, Otavio Exel wrote: >>Otavio Exel wrote: >> >>>I read in the awk man pages that awk supports grouping; >>>but how do I use the parts of the mach? >> > > Wayne <nospam(a)all4me.invalid> wrote: > >> >>That is a feature of Gnu awk (gawk): > > > Wayne, > > I'd rather not use "special" feature; > I'll find a way using sed. That may be the best advice or it may be terrible advice, depending on the nature of the problem you're trying to solve. There may be a reasonable way to do what you want in awk without using gawk-specific constructs. In the part that was snipped you said: >let's say I'd like to replace "<a,b>" with "<b,a>"; That's a simple, single line substitution so it's ideal for sed: $ echo "<a,b>" | sed 's/<\(.*\),\(.*\)>/<\2,\1>/' <b,a> but if you have anything else you want to do with the input text or if you have records that span multiple lines then you'd probably want to use awk and then you'd need to do something like: $ echo "<a,b>" | awk -F'[<>,]' '{print "<"$3","$2">"}' <b,a> or something else depending on what the rest of your input looked like. > but a very interesting question remains: > - why does awk support grouping than? > - IOW: what can you do with the "groups"? You group parts of an RE to perform operations on them. For example: awk '/abc(def|ghi)/' would print records that contain abcdef and/or abcghi and awk '/abc(def)?ghi/' would print records that contain abcdefghi and/or abcghi. Ed. |