#!/usr/bin/perl -w

use strict;

my %acronyms_captured;

my $file = 'test.txt';
open FH, "<", $file or die;

while(<FH>){
    my @words = $_ =~ m/\b[A-Z]+\b/g;
    foreach(@words) { $acronyms_captured{$_} = undef; }
}
close(FH);

foreach(keys(%acronyms_captured)){ print "$_\n"; }