The obligatory sick version:

my @array = ('file', 'this', 'dog', 'forward');
my %guard;
open IN, $Filename or die "$!: $Filename\n";
print join(' ', map {
    my $line = $_;
    grep {!exists $guard{$_} and $line =~/$_/ and $guard{$_}=1} @array
+;
} <IN>), "\n";
close IN;
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