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G'day ashes3d,

Welcome to the monastery.

Using the data you've provided, here's a blow-by-blow account of how to achieve what I believe you're after.

#!/usr/bin/env perl use 5.010; use strict; use warnings; # Simulate the 4 bytes of input binary data (i.e. from input file) my $in_data = pack 'B32' => '01011111111100000111000011111010'; # Create new leading byte with binary value of 1 my $lead_byte = pack 'B8' => '00000001'; # Concatenate leading and input bitstrings my $concat_bitstrings = unpack('B8', $lead_byte) . unpack('B32', $in_d +ata); # Create new data with 5 (1+4) bytes my $out_data = pack 'B40' => $concat_bitstrings; # Test it worked # Converting "0101_1111_1111_0000_0111_0000_1111_1010" # and "0000_0001_0101_1111_1111_0000_0111_0000_1111_1010" # to HEX format for ease of visualising/checking my $in_hex = '5ff070fa'; my $out_hex = '01' . $in_hex; # Print expected and actual results say 'Input'; say 'EXPECT: ', $in_hex; say 'GOT: ', unpack 'H*' => $in_data; say 'Output'; say 'EXPECT: ', $out_hex; say 'GOT: ', unpack 'H*' => $out_data;


$ Input EXPECT: 5ff070fa GOT: 5ff070fa Output EXPECT: 015ff070fa GOT: 015ff070fa

I'll assume you've found the doco for pack and unpack. There's also a tutorial you may not be aware of: perlpacktut.

-- Ken

In reply to Re^3: PERL Binary Data Handling by kcott
in thread PERL Binary Data Handling by ashes3d

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