mjhjmtu

I have a file instructions.txt with the contents:

00000000000000000000000000010011
00000010110100010010000010000011
00000000011100110000001010110011
00000000011100110000010000110011
00000000011100110110010010110011
00000000000000000000000000010011

How can I create a binary file instructions.bin of the same data as instructions.txt. In other words the .bin file should be the same 192 bits that are in the .txt file, with 32 bits per line. I am using bash on Ubuntu Linux. I was trying to use xxd -b instructions.txt but the output is way longer than 192 bits.

You were on the right track with xxd -b, but you need some other options too:

• 
  -p - use the "plain hexdump style"


• 
  -r - use the "reverse operation"

Be careful, because xxd doesn't accept multiple options (e.g: -bpr) - they need to be given separately.

$ cat instructions.txt
00000000000000000000000000010011
00000010110100010010000010000011
00000000011100110000001010110011
00000000011100110000010000110011
00000000011100110110010010110011
00000000000000000000000000010011
$ xxd -b -p -r < instructions.txt > instructions.bin
$ hexdump -Cv < instructions.bin
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 01 00 11 |................|
00000010 00 00 00 10 11 01 00 01 00 10 00 00 10 00 00 11 |................|
00000020 00 00 00 00 01 11 00 11 00 00 00 10 10 11 00 11 |................|
00000030 00 00 00 00 01 11 00 11 00 00 01 00 00 11 00 11 |................|
00000040 00 00 00 00 01 11 00 11 01 10 01 00 10 11 00 11 |................|
00000050 00 00 00 00 00 00 00 00 00 00 00 00 00 01 00 11 |................|
00000060

Adding the -r option (reverse mode) to xxd -b does not actually work as intended, because xxd simply does not support combining these two flags (it ignores -b if both are given). Instead, you have to convert the bits to hex yourself first. For example like this:

( echo 'obase=16;ibase=2'; sed -Ee 's/[01]4/;/g' instructions.txt ) | bc | xxd -r -p > instructions.bin

Full explanation:

• The part inside the parentheses creates a bc script. It first sets the input base to binary (2) and the output base to hexadecimal (16). After that, the sed command prints the contents of instructions.txt with a semicolon between each group of 4 bits, which corresponds to 1 hex digit. The result is piped into bc.


• The semicolon is a command separator in bc, so all the script does is print every input integer back out (after base conversion).


• The output of bc is a sequence of hex digits, which can be converted to a file with the usual xxd -r -p.

Output:

$ hexdump -Cv instructions.bin
00000000 00 00 00 13 02 d1 20 83 00 73 02 b3 00 73 04 33 |...... ..s...s.3|
00000010 00 73 64 b3 00 00 00 13 |.sd.....|
00000018
$ xxd -b -c4 instructions.bin
00000000: 00000000 00000000 00000000 00010011 ....
00000004: 00000010 11010001 00100000 10000011 .. .
00000008: 00000000 01110011 00000010 10110011 .s..
0000000c: 00000000 01110011 00000100 00110011 .s.3
00000010: 00000000 01110011 01100100 10110011 .sd.
00000014: 00000000 00000000 00000000 00010011 ....

oneliner to convert 32-bit strings of ones and zeros into corresponding binary:

$ perl -ne 'print pack("B32", $_)' < instructions.txt > instructions.bin

verify:

$ hexdump -Cv instructions.bin
00000000 00 00 00 13 02 d1 20 83 00 73 02 b3 00 73 04 33 |...... ..s...s.3|
00000010 00 73 64 b3 00 00 00 13 |.sd.....|
00000018