#!usr/bin/env perl

open  (      # open a filehandle
    test,    # called 'test'
    "@ARGV"  # pointing to file specified in arguments
);


while (      # Loop
    <test>   # read line from filehandle "test" and assign to $_
) {    
    $_ =~ <test>;  # 
    chomp;         # remove newline from end of $_
    s/(th)/TH/gi;  # Case insensitive replace 'th' with TH everywhere
    print "$_\n";  # print $_ with a new line
}