#!/usr/bin/perl

use 5.10.0;
use strict;
use warnings;

my %wanted;

while (my $line = <DATA>) {
    if ( $line =~ /\[start\]/ .. $line =~ /\[end\]/) {
        next if ($line =~ /\[start\]/ or $line =~ /\[end\]/);
        chomp $line;
        $wanted{$line}++;
    }
}
say $_ for sort keys %wanted;

__DATA__
[start]
bbc_arc_001
bbc_arc_002
abc_arc_001
[end]

bbc_arc_001
bbc_arc_002
bbc_arc_003
bbc_arc_004