[ I went sideways a bit since this is a learning exercise. Hopefully, this will put you in the right mindset to solve similar problems in the future. ]

My desired output to print 0b11110000 as 0xF0 but all I got was 0

This alone isn't very clear.

Is your input the string 0b11110000, the number 0b11110000 (240) or the character 0b11110000 (240)?

Is your desired output the string 0xF0, the number 0xF0 (240) or the character 0xF0 (240)?

One would generally convert the input to a number,

If your input is the string 0b11110000my $num = oct($input);
If your input is the number 240my $num = $input;
If your input is the character 240my $num = ord($input);
If your input is the character 240my $num = unpack('C', $input);

do something with it, then format the number as desired.

If your desired output is the string 0xF0my $output = sprintf("0x%02X", $num);
If your desired output is the number 240my $output = $num;
If your desired output is the character 240my $output = chr($num);
If your desired output is the character 240my $output = pack('C', $num);

Looking at your code, you want the the string 0xF0 from character 0b11110000, so 

printf("0x%02X", ord($input));

[download]
or 
printf("0x%02X", unpack('C', $input));

[download]

oct, ord, unpack, sprintf, printf, chr, pack

In reply to Re: Printing byte as 2 Hex characters by ikegami
in thread Printing byte as 2 Hex characters by ShiningPerl

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