Replacing with comma

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Replacing with comma
by Athanasius (Archbishop) on Dec 27, 2012 at 06:51 UTC

The {$r} in the regex is acting as a quantifier, not an index. It would be better to use split, splice, and join, like this:

#! perl
use Modern::Perl;

my $separator    = '|';
my $replacement  = ',';
my $target_count =  2;
my $line         = '1|2|3';
my $ft_count     =  0;

++$ft_count while $line =~ /\Q$separator\E/g;

if ($ft_count == $target_count)
{
    my @data = split /\Q$separator\E/, $line;
    splice(@data, $target_count - 1, 2, "$data[$target_count - 1]$repl
+acement$data[$target_count]");
    $line = join($separator, @data);
}

print $line, "\n";
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Output:

16:38 >perl 453_SoPW.pl
1|2,3

16:46 >
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See perlre for \Q...\E.

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re: Replacing with comma
by muba (Priest) on Dec 27, 2012 at 06:57 UTC

use strict;
use warnings;
use 5.010;
 
my $foo = "1,2,3";
substr($foo, rindex($foo,","), 1, "|");
say $foo;   # 1,2|3
 
$foo = "1|2|3";
substr($foo, rindex($foo,"|"), 1, ",");
say $foo;   # 1|2,3
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Re: Replacing with comma
by 2teez (Vicar) on Dec 27, 2012 at 07:37 UTC

You have been given great answers, but If I may add just this.
Using a subroutine with scalar, reverse functions with substitution s///. One can hack a solution like so:

use warnings;
use strict;

my $foo = "1,2,3";
print modify( $foo, ',', '|' );  ## prints 1,2|3

$foo = "1|2|3";
print modify( $foo, '|', ',' );  ## prints 1|2,3

sub modify {
    my ( $val, $sep, $rep ) = @_;
    $val = scalar reverse $val;
    $val =~ s/\Q$sep\E/$rep/;
    return scalar reverse $val;
}
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If you tell me, I'll forget.
If you show me, I'll remember.
if you involve me, I'll understand.
--- Author unknown to me

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Re: Replacing with comma
by 7stud (Deacon) on Dec 27, 2012 at 10:33 UTC

I need to reuse the code

First, you need to learn proper formatting. Use this code as a guide:

my $line = "1,2,3";
my $ft_count = 0;

$ft_count++ while($line =~ m/[,]/g);

if ($ft_count == 2) {
    my $n = 2;
    my $r = $n - 1;

    $line =~ s/((?:,.*?){}),/${1}|/;   
}

say $line;
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I need to reuse the code

1) Replace all occurrences of | in the code with a comma.

2) Replace all occurrences of a comma in the code with a |. However, the pipe has a special meaning in a regex, so if you literally want to match a pipe in a regex, then you have to escape it with a backslash. Or, you can put the pipe in a character class:

[|]
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... which will nullify its special meaning. The character class notation is easier to figure out than the hieroglyphics "\|", so I suggest you do that.

3) The substitution operator, s///, uses the syntax:

s/regex/string/

That means if you want to match a pipe character in the regex part of the s///, you must escape it or use it in a character class.