CODEWITHSUNDEEP
clinuxunix
titus
titus

Reputation: 5784

calling ls with execve

the following code should call a command with excve for some reason i doesn't print the contents of the current directory, but still the program returns "ok"

  1 #include <stdio.h>
  2 #include <unistd.h>
  3 int main ()
  4 { char *argv[]={"ls",NULL};·
  5   char *env[]={"PATH=/usr/local/sbin/:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games",NULL};
  6   if(execve("ls",argv,env))
  7   { printf("ok\n");
  8   }
  9   else
 10   { printf("not ok\n");
 11   }
 12   return 0;
 13 }

Upvotes: 3

Views: 12185

Answers (4)

iabdalkader
iabdalkader

Reputation: 17312

This doesn't really make much sense

if(execve("ls",argv,env) >0) {
    printf("ok\n");
} else {
    printf("not ok\n");
}

All exec functions do not return if they succeed, so if it returns it means it failed, you don't need to check if it returns -1, second issue is that the first argument to execve() is the file path not command name, from the man:

execve() executes the program pointed to by filename.

So you just need to:

execve("/bin/ls", argv, env);
/* execve() only returns on error */
perror("execve");   
exit(EXIT_FAILURE);

Upvotes: 2

paxdiablo
paxdiablo

Reputation: 882028

Since execve does not return on success, it's obvious that the call is failing somehow. It returns -1 on error, which would be treated as true (non-zero). That's why it's saying okay.

The most likely reason is that you haven't specified the full path to the executable, which is a requirement for execve. Alternatively, if you want the path to be searched, use execvpe instead. See http://linux.die.net/man/3/exec for the gory details.

Upvotes: 4

sshannin
sshannin

Reputation: 2825

Calls to exec don't return when they succeed. You basically replace the calling program with the one you're execing to.

So if you ever run any code past the exec, it means exec failed. I believe exec returns -1, which is why you end up printing ok.

Upvotes: 2

davmac
davmac

Reputation: 20641

execve returns -1 on error, which evaluates as true when used in a context requiring a boolean. However, there's no point checking the return value, since if execve succeeds then it won't return.

Probably in this case, it's failing because you're not supplying the full path to 'ls'.

Upvotes: 1

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