Determine whether a file is a binary executable file or a script file using gcc in Linux

Question

In Linux both a binary executable file and a script can be marked "executable". I would like to determine in my gcc program whether the file is a script or a binary executable.

I read that there is an a.out.h file which allows to analyse the header of the file but I do not know how to use this in my code. Or if there is a simple solution instead.

man access will tell you if it's executable. Reading some number of bytes will tell if it's ascii or binary. man magic might be of interest too. — Charlie Burns
– Charlie Burns, Commented Nov 24, 2013 at 20:01
There's no such thing as a "gcc program". You may mean a "C program" that you compiled with GCC. — Jonathon Reinhart
– Jonathon Reinhart, Commented Nov 24, 2013 at 20:03
Consider whether you really need to do this. The whole point of scripts is that they can be executed as if they were binary executable programs. — Keith Thompson
– Keith Thompson, Commented Nov 24, 2013 at 20:28

luk32 · Accepted Answer · 2013-11-24 20:08:56Z

5

You can check so-called magic bytes. For elf 1st four bytes are supposed to be 7f 45 4c 46 in hex. You have to care for byte order though.

Opening file in binary mode and reading 1st four bytes should suffice.

E.g.

shell$ hexdump -n 10 ./ni6_ga 0000000 457f 464c 0101 0301 0000

edited Nov 24, 2013 at 20:08

answered Nov 24, 2013 at 20:01

luk32

16.1k2 gold badges42 silver badges67 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Jonathon Reinhart Over a year ago

Whereas a script will start with #!

Keith Thompson Over a year ago

@JonathonReinhart: Not necessarily. An executable text file that doesn't start with #! is treated as a /bin/sh script. (Retroactively following up to your followup, it's certainly good practice to use the #! anyway.)

Jonathon Reinhart Over a year ago

@KeithThompson Indeed. I forgot about that (as I think it is "good practice" to include the she-bang, regardless).

Georg Over a year ago

I usually write my shell scripts without #! and they run fine. So to check for that seems to be not reliable. The a.out.h file has a NMAGIC() macro to check the magic bytes. Has anyone used that yet? (And maybe has an example for that?)

Georg Over a year ago

The macros I mentioned refer to the older a.out executable format. For the common ELF format luk32's answer is correct and sufficient.

|

Collectives™ on Stack Overflow

Determine whether a file is a binary executable file or a script file using gcc in Linux

1 Answer 1

6 Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Related