Strip out the bit you want and put it in a hash. Then put the decoration back when you use it.

#! perl -slw
use strict;

my %filters;
@filters{ ( split ',' )[1] =~ m[//\*\.([^*]+)\*] } = 1
    while <DATA> ;

printf "http://*.%s*/*\n", $_ for keys %filters;

=output
C:\test>826863
http://*.google.com*/*
http://*.gmail.com*/*
http://*.yahoo.com*/*
=cut


__DATA__
parm1,http://*.google.com*/*,parm3
parm1,http://*.google.com*/*,parm3
parm1,http://*.yahoo.com*/*,parm3
parm1,http://*.google.com*/*,parm3
parm1,http://*.gmail.com*/*,parm3
parm1,http://*.yahoo.com*/*,parm3
parm1,http://*.google.com*/*,parm3
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