The following documents should take you two or three hours to read through. After that, it will not be necessary for you to ask us every time you need a simple regexp solution to parsing a simple text file.

• perlintro
• perlretut
• perlopentut

If after that you still need additional info you can look at the following:

• perlsyn
• perlsub
• perlre
• open

Ok, that's going to be another four or five hours of reading. But you want to learn this stuff right? Eight hours of free documentation to read and you'll avoid having to ask when your specification changes to want to replace a space followed by a newline with a comma and an asterisk. My point is that each of the questions you've asked may indeed be different questions. But it's like asking, "Now what if I want the elevator to go to the third floor, what do I do then?" And then a day later, "But what if I want it to go to the fourth floor? How would I do that?" And then... "Ok, here's a good one for you. What if I want the elevator to go to the fifth floor?" You can do better than that, I'm confident.

Perhaps in my sleep deprived state I'm overlooking something, but I believe that following work:

use strict;
use warnings;

my $text = "I love\tmy nation.";
$text =~ s/\t/,/g;
print "$text";
[download]

Output: I love,my nation.

However, if those are actually 8 spaces instead of an actual tab, the regex in my code won't work. In that case, you'd probably want to do something along the lines of what Nikhil Jain posted.

use strict;
use warnings;
my $string = "I love     my nation";
#leaving one space and substitute 2 or more spaces with comma globally
$string =~ s/\s{2,}/,/g; 
print "$string\n";
[download]

Output: