Is there a command to modify a binary file in the shell?
First, I created a file with all 0xFF values:
dd if=/dev/zero ibs=1K count=1 | tr "\000" "\377" > ./Test.img
hexdump Test.img
Output:
0000000 ffff ffff ffff ffff ffff ffff ffff ffff
*
0000400
Then I wanted to change some byte value like
0000000 aaaa ffff bbbb ffff cccc ffff ffff ffff
*
0000400
How can I change that? Or is there a command in shell script?
Python was designed to be binary-clean, so here is one approach:
python -c 'open("New.img", "wb").write( "\xaa\xaa\xff\xff\xbb\xbb\xff\xff\xcc\xcc" + open("Test.img", "rb").read()[10:] )'
We can use hexdump to view the resulting file:
hexdump New.img
Output:
0000000 aaaa ffff bbbb ffff cccc ffff ffff ffff
0000010 ffff ffff ffff ffff ffff ffff ffff ffff
*
0000400
The shell is not binary-clean. For example, no shell string can contain the character \x00. Consequently, any approach using shell may be subject to unpleasant surprises. However, if one must, try:
LC_ALL=C; { printf "%s" $'\xaa\xaa\xff\xff\xbb\xbb\xff\xff\xcc\xcc'; tail -c+11 New.img; } >New2.img
You can just use vim -b bin-file-name. This would start Vim in binary mode, which allows you to do anything to any file, as long as you know what you are doing.
