You need to use strict and warnings. You are trying to compare two things that aren't actually numbers (as they have a comma in them). If you had warnings on you'd get something like:

Argument "1,900" isn't numeric in sort at sort.pl line 7, <DATA> line 
+3.
Argument "4,900" isn't numeric in sort at sort.pl line 7, <DATA> line 
+3.
Argument "1,333,987" isn't numeric in sort at sort.pl line 7, <DATA> l
+ine 3.
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You also don't need to use $main::a and $main::b as $a and $b are special and are globals.

You probably want to do something like:

@sorted = sort {$a->[2] <=> $b->[2]} map { s/,//g; $_ } @sorted;
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You might want to look up the Schwartzian Transform or perldoc sort.

gav^