Substitute (s///) a set of times

Description:

This subroutine will s/// a set number of times.

The obvious solution would seem to be: s/\Gpattern/blah/ while $count--, but that does not work because \G only works with m//, and s/(a)/<$1$1>/ while $count-- would restart the match each time at the beginning. (pos=0)

Usage is: subtimes($string, $number_of_times, $pattern, $string_to_substitute). You can include $dollar variables in $string_to_substitute, just make sure to remember to backslash the dollar variable in the string.

For instance, this: print subtimes("ababa", 2, qr/(a)/,"<\$1\$1>"); would print "<aa>b<aa>ba".

Update: Fixed a bug.

print subtimes($string, 2, qr/(a)/,"<\$1\$1>");

sub subtimes {
    my ($string, $count, $find, $tosub) = @_;
    no strict "refs";
    
    my $newstring;
    while ($count--) {
        next unless $string =~ /($find)/;
        my ($num,%res) = 2;
        $res{$num++}=$$num while defined $$num;
        my ($matched, $startoffset, $endoffset, $temp) = ($1, $-[0], $
++[0], $tosub);

        $temp =~ s/\$(\d+)/my $r=$1;$r++;$res{$r}/ge;
        $newstring .= substr($string, 0, $startoffset).$temp;
        substr($string, 0, $endoffset) = '';
    }
    return $newstring.$string;
}

Comment on Substitute (s///) a set of times Download Code

Replies are listed 'Best First'.
Re: Substitute (s///) a set of times by runrig (Abbot) on Sep 04, 2004 at 01:02 UTC
This is not very well tested, but how about: `use re 'eval'; my $str = "111111111"; my $times = 5; my $re = qr/1/; my $cnt; $str =~ s/$re(?(?{++$cnt > $times})\A)/2/g; print "$str\n";` [download] Turning this into a subroutine is left as an exercise.	[reply] [d/l]
Re^2: Substitute (s///) a set of times by demerphq (Chancellor) on Sep 06, 2004 at 20:09 UTC
IMO its a bad habit to use lexicals in such constructs. They will only work once. For instance your code will not work properly if naively converted to a subroutine. The `$cnt` var needs to be a package scoped var. Otherwise what happens is that the regex is compiled once and the first $cnt will be enclosed into the (?{}), on the second run the new $cnt is not used, rather the original will be used. So for instance `use re 'eval'; sub limited_re { my $str=shift; my $re=shift; my $repl=shift; my $times=shift; our $cnt; local $cnt=0; $str =~ s/$re(?(?{++$cnt > $times})\A)/eval $repl/ge; print "$str\n"; } limited_re("111111111",qr/1/,5,2); limited_re("000000000111111111",qr/1/,2,5);` [download] Works as expected. Change the `our $cnt; local $cnt=0;` to a `my $cnt;` and it won't. I got bitten by this when working on a solution for QOTW 23 (which happens to be on my pad at the time of posting this.) --- demerphq _{First they ignore you, then they laugh at you, then they fight you, then you win. -- Gandhi}	[reply] [d/l] [select]
Re^3: Substitute (s///) a set of times by runrig (Abbot) on Sep 09, 2004 at 22:19 UTC
Thanks, I did not realize the dangers of lexicals in this situation. Though in order to get the capture variable behavior of the OP's code, I made the following changes: `... $str =~ s/$re(?(?{++$cnt > $times})\A)/qq["$repl"]/gee; ... limited_re("111111111",qr/(1)/,'${1}5',2);` [download] Though it would have worked with the code as it was if you included double quotes inside the single quotes of the replacement string, e.g., `'"${1}5"'`.	[reply] [d/l] [select]


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