Question

I have binary and want to extract part of it, starting from know byte string (i.e. FF D8 FF D0) and ending with known byte string (AF FF D9)

In the past I’ve used dd to cut part of binary file from beginning/ending but this command doesn’t seem to support what I ask.

What tool on terminal can do this?

Answer 1

In a single pipe:

xxd -c1 -p file |
  awk -v b="ffd8ffd0" -v e="aaffd9" '
    found == 1 {
      print $0
      str = str $0
      if (str == e) {found = 0; exit}
      if (length(str) == length(e)) str = substr(str, 3)}
    found == 0 {
      str = str $0
      if (str == b) {found = 1; print str; str = ""}
      if (length(str) == length(b)) str = substr(str, 3)}
    END{ exit found }' |
  xxd -r -p > new_file
test ${PIPESTATUS[1]} -eq 0 || rm new_file

The idea is to use awk between two xxd to select the part of the file that is needed. Once the 1st pattern is found, awk prints the bytes until the 2nd pattern is found and exit.

The case where the 1st pattern is found but the 2nd is not must be taken into account. It is done in the END part of the awk script, which return a non-zero exit status. This is catch by bash‘s ${PIPESTATUS[1]} where I decided to delete the new file.

Note that en empty file also mean that nothing has been found.