The functionality which you seek is provided by the Expect module. For example:

use Expect;

my $process = Expect->spawn( '/usr/bin/passwd');
$process->expect( 10, "Password:" );
$process->send( "changeme\n" );
$process->send( "newpass\n" );
$process->send( "newpass\n" );
$process->expect( undef );
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Alternatively, if you find the interface to this module overly complex, you may want to investigate the Expect::Simple module.

 

perl -le 'print+unpack("N",pack("B32","00000000000000000000001000000100"))'