This performs bit mask operations upon 32-bit values thereby saving the need to ascii-ize the binary.

#! perl -slw
use strict;

sub getBits {
    my( $N32, $offset, $bits ) = @_;
    my $mask = 1 << $bits;
    $mask--;
    $mask <<= $offset;
    return ( $N32 & $mask ) >> $offset;    
}

## Encode some test data.
my $data = unpack 'N', pack 'b*', 
#0123456789 123456789 123456789 1
'11101111101111111011111111101111';
#  7    31     127       511   15

print $data; ## 4160617975

print getBits( $data, 0, 3 ); ## Should be 7
print getBits( $data, 4, 5 ); ## should be 31
print getBits( $data, 10, 7 ); ## Should be 127
print getBits( $data, 18, 9 ); ## Should be 511
print getBits( $data, 28, 4 ); ## Should be 15

__END__
P:\test>test
4160617975
7
31
127
511
15
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