I'll include the entire thing here and --sorry I'm still not with the wiki style for 'code' tags. I'll get it eventually.

#!usr/bin/env perl
open (test, "@ARGV");
while (<test>) {
$_ =~ <test>;
chomp;
s/(th)/TH/gi;
print "$_\n";
}
close (test);
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The open is for reading and surely you mean

open(test, "<$ARGV[0]"); # what happens when more args?
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This, I believe is the issue so instead of this

    s/(th)/TH/gi;
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try this

    s/th/TH/go;
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Its likely that a simpler

    tr/th/TH/;
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might work.