What is the extension of output files of gcc operation?

Question

If I do gcc filename.c, I get a.out

After performing gcc -o output_name filename.c we get the executable file output_name.

What is the extension of this file?

Answer 1

Unlike windows, Linux does not depend upon extension of a file to determine what type of file it is. Instead, it will check first few bytes of the file and determine what type of file it is.

Hence the output file given by gcc requires no extension. You may add whatever extension you want(by changing -o output_name to say -o output_name.abcd), but it is not going to mke any difference.

You can have a look at the output of the command

file ./filename

for example

:~$ file output_file 
output_file: ELF 32-bit LSB  executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.24, BuildID[sha1]=9bc9fabf05a3d2e58c7780c48cd873cb2955b2ec, not stripped
:~$ 

Answer 2

It does not have one. You can do gcc -o myprog.exe filename.c and it will be called myprog.exe. Unlike Windows there is no default extension for executable files on Linux. If you want to mark a file as executable do chmod +x file.

ls -l shows you if the x (executable) flag is set for your file:

user@host# ls -l filename
-rwxr-x--x 1 ubu users 42 Mai 10 08:16 filename

- means its a file (d would be directory,see below)
r means readable
w means writeable
x means executable

The first triple is for the owner (ubu in this case), the second triple is for the owning group (users) and the last triple is for everyone else.

For directories the x means "can enter directory", so if x is not set you cannot do cd directory.

On Linux File Extensions are not special, the are just part of the files name.