Passing binary data as arguments in bash

Question

I need to pass binary data to a bash program that accepts command line arguments. Is there a way to do this?

It's a program that accepts one argument:

script arg1

But instead of the string arg1, I'd like to pass some bytes that aren't good ASCII characters - in particular, the bytes 0x02, 0xc5 and 0xd8.

How do I do this?

score 27 · Accepted Answer · answered Feb 28 '12 at 17:57

27

script "`printf "\x02\xc5\xd8"`"
script "`echo -e "\x02\xc5\xd8"`"

test:

# echo -n "`echo -e "\x02\xc5\xd8"`" | hexdump -C
00000000  02 c5 d8                                          |...|

answered Feb 28 '12 at 17:57

Karoly Horvath

3

I believe your test is equivalent to the simpler `echo -ne "\x02\xc5\xd8" | hexdump -C` :-) – elimisteve Nov 29 '12 at 05:27
2

Not quite... here I'm trying to simulate the actual call of `script`, by replacing it with `echo -n` – Karoly Horvath Nov 29 '12 at 12:04

score 26 · Answer 2 · answered Feb 29 '12 at 13:27

26

Use the $'' quote style:

script $'\x02\xc5\xd8'

Test:

printf $'\x02\xc5\xd8' | hexdump -C
00000000  02 c5 d8

answered Feb 29 '12 at 13:27

l0b0

`$''` is Bash mechanism for quoting [ANSI C like strings](http://wiki.bash-hackers.org/syntax/quoting#ansi_c_like_strings) – UrsaDK Dec 24 '18 at 15:46

jordanm · Answer 3 · 2012-02-28T17:54:12.147

6

Bash is not good at dealing with binary data. I would recommend using base64 to encode it, and then decode it inside of the script.

Edited to provide an example:

script "$(printf '\x02\xc5\xd8' | base64 -)"

Inside of the script:

var=$(base64 -d -i <<<"$1")

edited Feb 28 '12 at 17:54

answered Feb 28 '12 at 17:48

jordanm

2

Agreed. I haven't found any way to get bash to deal with zero bytes (\x00) in strings, and it tends to add/remove trailing newlines (\x0a) as it thinks best -- both are quite bad when dealing with arbitrary binary data. – Gordon Davisson Feb 28 '12 at 18:14

Bartosz Moczulski · Answer 4 · 2012-02-28T18:02:17.930

0

How about this?

$ script "`printf "\x02\xc5\xd8"`"

edited Feb 28 '12 at 18:02

answered Feb 28 '12 at 17:47

Bartosz Moczulski

3

you don't want bash to process the argument... `script "\`printf "\x02\xc5\xd8"\`"` – Karoly Horvath Feb 28 '12 at 17:49
@yi_H Good point. Fix applied, which leads directly to your answer :) – Bartosz Moczulski Feb 28 '12 at 18:02

Eduardo Ivanec · Answer 5 · 2012-02-28T18:03:20.520

-1

Save your binary data to a file, then do:

script "`cat file`"

edited Feb 28 '12 at 18:03

answered Feb 28 '12 at 17:48

Eduardo Ivanec

UUOC. How about script $( – jordanm Feb 28 '12 at 17:50
@Cam what are you doing inside of the script? What is your expected results? – jordanm Feb 28 '12 at 17:55
@jordanm: isn't $( – Eduardo Ivanec Feb 28 '12 at 18:00
It's a bash specific extension. This question is only tagged bash, so presumably he would have #!/bin/bash at the top of his script. – jordanm Feb 28 '12 at 18:03

5 Answers5