How to create binary file using Bash?

Question

How can I create a binary file with consequent binary values in bash?

like:

$ hexdump testfile
0000000 0100 0302 0504 0706 0908 0b0a 0d0c 0f0e
0000010 1110 1312 1514 1716 1918 1b1a 1d1c 1f1e
0000020 2120 2322 2524 2726 2928 2b2a 2d2c 2f2e
0000030 ....

In C, I do:

fd = open("testfile", O_RDWR | O_CREAT);
for (i=0; i< CONTENT_SIZE; i++)
{
    testBufOut[i] = i;
}

num_bytes_written = write(fd, testBufOut, CONTENT_SIZE);
close (fd);

this is what I wanted:

#! /bin/bash
i=0
while [ $i -lt 256 ]; do
    h=$(printf "%.2X\n" $i)
    echo "$h"| xxd -r -p
    i=$((i-1))
done

Answer 1

There's only 1 byte you cannot pass as argument in bash command line: 0 For any other value, you can just redirect it. It's safe.

echo -n $'\x01' > binary.dat
echo -n $'\x02' >> binary.dat
...

For the value 0, there's another way to output it to a file

dd if=/dev/zero of=binary.dat bs=1c count=1 

To append it to file, use

dd if=/dev/zero oflag=append conv=notrunc of=binary.dat bs=1c count=1