Although others have shown better solutions, The original post is nearly correct. The only problem is that the logic is backwards.

#!/usr/bin/perl -w
use strict;
@ARGV = qw(a b c c d);    #remove the extra "c"

my @inputs = ();
my @values = ();

@inputs = @ARGV;

foreach my $elemnt (@inputs)
    {

#   if (grep {$_ ne $elemnt} @values)
    if (!grep {$_ eq $elemnt} @values)
        { push @values, $elemnt; }
    }

print "@values\n";
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