my @in;
while (<>) {
    push @in, $1 if /(\$[A-Za-z_]\w*)/;
}

##</code><code>##

while (<>) {
    push @in, /(\$[A-Za-z_]\w*)/g;
}

##</code><code>##

my %hsh;
@hsh{@in} = ();
print $_, $/ for keys %hsh;

##</code><code>##

my %hsh;
@hsh{ /(\$[A-Za-z_]\w*)/g } = () while <>;
delete $hsh{''};  # tidy up
print $_, $/ for keys %hsh;