Another, not necessarily better, way to "replace every x after the first with y" (needs Perl 5.10+):

>perl -wMstrict -le
"for my $s (
   'ABC,XYZ PERL,, IS, AWESOME, INNIT',
   ',ABC,XYZ PERL,, IS, AWESOME, INNIT,',
   ',,ABC,XYZ PERL,, IS, AWESOME, INNIT,',
   ) {
   print qq{ in: '$s'};
   ;;
   (my $t = $s) =~ s{ (?: \A [^,]* , (*SKIP)(*FAIL))? , }{}xmsg;
   print qq{out: '$t'};
   print '';
   }
"
 in: 'ABC,XYZ PERL,, IS, AWESOME, INNIT'
out: 'ABC,XYZ PERL IS AWESOME INNIT'

 in: ',ABC,XYZ PERL,, IS, AWESOME, INNIT,'
out: ',ABCXYZ PERL IS AWESOME INNIT'

 in: ',,ABC,XYZ PERL,, IS, AWESOME, INNIT,'
out: ',ABCXYZ PERL IS AWESOME INNIT'
[download]