AgentM had pretty much the complete list (except chop). Your question, however, is not really specific enough to do more then point you at these documents. But I suspect, rather... HOPE, that you looked at the library before posting your question and have therefor seen these documents (chop,chomp,tr,s) so you probably wanted an example. Lets see:

use strict; #Always!

my $string = "This is a test string. 123\n";

chomp($string); # removes the "\n" from the end of $string.
chomp($string); # no-op. chomp only removes white-space: \t, ' ', \n, 
+etc...
chop($string);  # removes the '3' from the end of $string.
chop($string);  # removes the '2'... get the idea?
print $string, $/; # print the string, and a new-line.

$string =~ s/a //; # replaces an appearance of 'a ' with ''
print $string, $/; # print the string, and a new-line.
                   # should read: "This is test string. 1"

$string =~ tr/.//d; # remove all periods.
print $string, $/;

$string =~ s/.$//; # removes the last char. slower then chop.
$string =~ s/..$//; # removes the last two characters.

my $n = 6;
$string =~ s/.{$n}$//; # removes the last $n characters.
print $string, $/;
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