use strict; 
use warnings;

my $str = 'abcdefghijklmnop';

sub shrink {
    my $bitstr = unpack('B*', $_[0]);
    $bitstr =~ s/.(.{7})/$1/g;
    pack('B*', $bitstr);
}

sub grow {
    my $bitstr = unpack('B*', $_[0]);
    $bitstr =~ s/(.{7})/0$1/g;
    pack('B*', $bitstr);
}

my $shrunk = shrink($str);
printf "Was: %s, Is: %s\n", length($str), length($shrunk);
printf "Restored: <%s>\n", grow $shrunk;