RE: RE: Selective substitution: not in Perl?

[nuance]

That doesn't work, suppose I have the string "abacab" and want to replace the second a with an upper case A. Your regex doesn't match. How about this (untested):

#!/usr/bin/perl -w

use strict;

my $string = "abacab";
print "$string\n";

my $pattern = "a";
my $better = "A";
my $n=1;
my $i=0;

$string =~ s/($pattern)/$i == $n ? $better : $1; i++/ge;

print "$string\n"

Nuance

[atl]

Black magic! I'm really impressed, I didn' know you can put that all into the substitution pattern. /me bows to Nuance ...

As for my solution, I was focused on the sample input given, I didn't think of the more general problem. But you're right about this.

As for your script, it works with a small alteration:

$string =~ s/($pattern)/$i++ == $n ? $better : $1/ge;

If you increment $i in a seperate statement, the whole block evaluates to the value of $i und you get

abacab
0b1c2b

Ok, now we're having fun :-)...

Andreas (waiting for the chinese food delivery service ...)

[merlyn]

To make it even clearer, remember that the right side of the s///ge can be an arbitrary block. Here's the "Perl Bowling" style written for clarity:

{ my $count = 0;
  $string =~ s{($pattern)}{
    my $source = $1;
    $count++;
    if ($count == $target) {
      $source = $replacement; # replace!
    }
    $source;  # either original or replacement now
  }ge;
};

And yes, you can actually write it like that, just as you see. If you're doing anything odd in the right hand side in a s///e, I recommend expanding it out like that.

-- Randal L. Schwartz, Perl hacker

[Anonymous Monk]

Thanks, your solution works great! I wrote a sub to convert sed-ish s///n constructs to your format, making conversion from sed easier:

sub seval
{
    my ($sub) = shift;
    $vni++;
    $sub =~ s#s/([^/]+)/([^/]+)/(.+)#s/\1/\$i$vni++ == \3 ? \2 : \$&/e
+gs#;
    return $sub;
}
# Evals 's/foo/$i1++ == 1 ? bar : $&/egs'
eval(seval("s/foo/bar/2"));

Thanks again.