Hexfilter

Read/Write non-printable characters in a printable way.

Synopsis

hexfilter COMMAND [ARG]...

hexfilter was originally developed for cracking. It's not rare when you need to input raw hex values in cracking something, usually it is done by echo or printf. Use echo or printf to generate the hex string and redirect it to a temp file, then cat the file as stdin. However, this way does not work if you need to input interactively. Yes, hexfilter is exactly for this.

hexfilter takes over subcommand's stdin, stdout and stderr, parses non-printal characters in stdout/stderr to '\xXX' format and prints it to terminal. Also it accepts the same '\xXX' format for inputing hex characters, converts and passes it to subcommand.

Compile

hexfilter depends on C POSIX library only as you can compile it on UNIX-like system by

gcc -o hexfilter hexfilter.c

Or if you prefer clang, nothing will change

clang -o hexfilter hexfilter.c

If a Makefile turns out to be necessary, I'll write it, but now I want to keep everything in a simplest way.

Example

Read

$ echo -ne 'ab\xff\xfe\n' >/tmp/input
$ cat /tmp/input
ab??                      # can't properly print '\xff' and '\xfe'
$ ./hexfilter cat /tmp/input
ab\xff\xfe                # binary byte '0xff' and '\xfe' are printed as human-readable strings

Write

$ ./hexfilter tee /tmp/output >/dev/null
ab\xff\xfe                # input hexadecimal value as plain string '\xff' and '\xfe'
^C
$ hexdump /tmp/output
0000000 61 62 ff fe 0a    # actually in file are exactly those hex characters
0000005

TODO

1. End stdin when CTRL-D is pressed. (The conventional way to end input but not supported yet)
2. Handle redirection and pipe for subcommand.

Contribute

I think it is an useful tool but I don't have much time to improve it. Your contribution is really welcome!