You don't need to have the intermediate 'a' and 'b' chars, you could either turn 0s and 1s into the corresponding nibble explicitly: 

$stream =~ s/0/0000 /g;
$stream =~ s/1/1111 /g;

[download]
(perl only searches in the part of the string that wasn't already modified, so the 0s in "0000 " aren't turned again).

Or you could use the power of regexes: 

$stream =~ s/(.)/$1$1$1$1 /g; # could be rewritten using /e and x 4

[download]
Or, if you're fine with hex representation, turn the 1s into F: 
$stream =~ tr/1/F/;
print "0x$stream\n";

[download]
0x0000
0x000F
0x00F0
0x00FF
0x0F00
0x0F0F
0x0FF0
0x0FFF
0xF000
0xF00F
0xF0F0
0xF0FF
0xFF00
0xFF0F
0xFFF0
0xFFFF

[download]

++ for your solution nevertheless :)

In reply to Re^2: Bit manipulation of a bit stream to generate different elements of an array with each nibble taking either 0 or 1 in perl by Eily
in thread Bit manipulation of a bit stream to generate different elements of an array with each nibble taking either 0 or 1 in perl by spriyada29

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