Your loop is

while (1) {
   ...
}
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Ctrl-Z does not change the value "1" returns.

As for your original question,

my @a;
while (my $val = <>) {
   chomp $val;
   push @a, $_ if !grep $_ eq $val, @a;
}
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or

my @a;
my %seen;
while (<>) {
   chomp;
   next if $seen{$_}++;
   push @a, $_;
}
[download]