You are using $_ from @res instead of using $_ from outer for loop in grep statement.
Instead try this 
perl -le '@arr=qw(a b a c);
my @res;
foreach(@arr) { $__=$_;$ans= grep /^$__$/,@res;
print "\$_: $_ ans: $ans";push @res,$_ unless $ans;}
 print "@res"'

$_: a ans: 0
$_: b ans: 0
$_: a ans: 1
$_: c ans: 0
a b c

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In reply to Re: Braino - why is this not working? by suhailck
in thread Braino - why is this not working? by perl-diddler

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