Re: Perl substitute with the nth match

> OF COURSE I can do this in a loop. Or with a /e

Can you? I can, too:

perl -pe 's/cat/++$i/ge' file
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There's no special variable that counts matches. But there's one that's incremented with each line of input: $.. So if we could tell Perl that cat instead of a newline is the line delimiter... but of course we can do that! That's what $/ is for.

perl -pe 'BEGIN { $/ = "cat" } chomp; $_ .= $. unless eof' file
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Update: which can be rewritten to use substitution as you originally wanted:

perl -pe 'BEGIN { $/ = "cat" } s{$/}{$.}' file
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map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

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Re^2: Perl substitute with the nth match by LanX (Saint) on Jan 13, 2023 at 13:50 UTC
> > OF COURSE I can do this in a loop. > `s/cat/++$i/ge` interestingly it's possible to avoid `/e` in an efficient inside-out (TIMTOW) loop version of `m///` `say pos($txt) while $txt =~ m/cat/g` Now with `s///` this kind of works, but isn't efficient because `pos` will be reset each time `use v5.12; use warnings; use Data::Dump qw/pp dd/; my $txt = <<'___'; cat dog cat mouse eel cat housecat catamaran fish ___ say 'm-pos:', pos($txt) while $txt =~ m/cat/g; my $cnt=1; while ($txt =~ s(cat)($cnt)x) { say "s-pos:", pos($txt) // "undefined"; $cnt++; } say $txt;` [download] `m-pos:3 m-pos:11 m-pos:25 m-pos:34 m-pos:38 s-pos:undefined s-pos:undefined s-pos:undefined s-pos:undefined s-pos:undefined 1 dog 2 mouse eel 3 house4 5amaran fish` [download] and no, using `s///g` would do the outer loop only once, tho there might be a way to force a single replace with `(?FAIL)` ... probably? Cheers Rolf _{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]

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Re^2: Perl substitute with the nth match
by LanX (Saint) on Jan 13, 2023 at 13:50 UTC

> > OF COURSE I can do this in a loop.

> s/cat/++$i/ge

interestingly it's possible to avoid /e in an efficient inside-out (TIMTOW) loop version of m///

say pos($txt) while $txt =~ m/cat/g

Now with s/// this kind of works, but isn't efficient because pos will be reset each time

use v5.12;
use warnings;
use Data::Dump qw/pp dd/;

my $txt = <<'___';
cat
dog
cat
mouse
eel
cat
housecat
catamaran
fish
___


say 'm-pos:', pos($txt) while $txt =~ m/cat/g;


my $cnt=1;

while ($txt =~ s(cat)($cnt)x) {
    say "s-pos:", pos($txt) // "undefined";
    $cnt++;
}

say $txt;
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m-pos:3
m-pos:11
m-pos:25
m-pos:34
m-pos:38
s-pos:undefined
s-pos:undefined
s-pos:undefined
s-pos:undefined
s-pos:undefined
1
dog
2
mouse
eel
3
house4
5amaran
fish
[download]

and no, using s///g would do the outer loop only once, tho there might be a way to force a single replace with (?FAIL) ... probably?

Cheers Rolf
_{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :)

Wikisyntax for the Monastery}

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