my execv() function not working in linux ubuntu

Question

I wrote the following code but I always get the output: "ERROR!" (the execv function not scheduled to return)

What am I doing wrong???

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <math.h>
#include <string.h>
#include <malloc.h>
#include "LineParser.h"

#define LOCATION_LEN 200
char* getL(void);

int main(int argc,char *argv[])
{
    char *loc = getL();
    char *args[] = {loc,"ls",NULL};
    int i;
    execv(args[0],args);
    printf("ERROR!");
    free(loc);
}

char* getL(void)
{
    char *buff = (char**)malloc(sizeof(char)*LOCATION_LEN);
    getcwd(buff,LOCATION_LEN);
    return buff;
}

First off, check errno on the return from `execv`. Then check the parameters that you are passing. — Duck, Oct 05 '14 at 14:38
Of course it is returning -1. Use `errno` and `strerror` or `perror` to explain why...namely your parameters. — Duck, Oct 05 '14 at 15:49
What is the real purpose and the motivation of your program? We could guess some of it wrongly! — Basile Starynkevitch, Oct 05 '14 at 16:05
BTW, you should remove `#include ` since `malloc` is declared from `#include ` — Basile Starynkevitch, Oct 05 '14 at 19:32

score 3 · Answer 1 · edited Apr 29 '17 at 09:30

Read documentation of execv(3) and of execve(2) and of perror(3). At the very least, you should code

int main(int argc, char *argv[]) {
  char *loc = getL();
  char *args[] = { loc, "ls", NULL };
  int i;
  execv(args[0], args);
  perror("execv");
  free(loc);
}

You should compile with gcc -Wall -g then use the gdb debugger.

Your usage of execv is obviously wrong (you need a full path, e.g. "/bin/ls", and the order of arguments is wrong). You probably want exevcp(3) and you should in fact code at least:

  char *args = { "ls", loc, NULL };
  execvp("ls", args);
  perror("execvp")

If you insist on using specifically execv(3) you could try

  char *args = { "ls", loc, NULL };
  execv("/bin/ls", args);
  perror("execv")

I don't understand what your code is supposed to do. You might be interested by glob(7) & glob(3).

You probably should read Advanced Linux Programming. It seems that there are several concepts that you don't understand well enough. I guess that strace(1) could be useful to you (at least by running strace ls *.c to understand what is happening).

Maybe your getL is exactly what the GNU function get_current_dir_name(3) is doing, but then the (char**) cast inside it is grossly wrong. And you should better clear the buffer buff using memset(3) before calling getcwd(2) (and you should test against failure of ̀ mallocand ofgetcwd`)

Perhaps you want opendir(3), readdir(3), asprintf(3), stat(2); with all these, you could even avoid running ls

If you are coding some shell, you should strace some existing shell, and after having read all the references I am giving here, study the source code of free software shells like sash and GNU bash

thanks But must use in execv so can you please explain to me how it works? I did not understand the function parameters. — Roni, Oct 05 '14 at 16:12
Read all the links I gave you (that should take several hours of reading). I won't try to explain what the references I gave you are explaining better than I could explain in a few minutes. And please *edit your question* to *improve it*. — Basile Starynkevitch, Oct 05 '14 at 16:17
I tried what you said But it still does not work http://www.siz.co.il/my.php?i=yme2vgnyyt1y.png — Roni, Oct 05 '14 at 16:41
Your image show `/bin/is` (with a I lower-case) but it should be `/bin/ls` (with an L lower-case), which is given by `which ls` — Basile Starynkevitch, Oct 05 '14 at 16:43

score 0 · Answer 2 · answered Oct 05 '14 at 15:32

0

You are not passing the correct arguments to execv. The first argument must be a path to the executable you wish to run but you are passing the path to the current working directory.

Update getL to return the full path to ls.

answered Oct 05 '14 at 15:32

R Samuel Klatchko

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what is the full path to ls? – Roni Oct 05 '14 at 15:38
1

Run `which ls` in a terminal to know that. very often it is `/bin/ls` – Basile Starynkevitch Oct 05 '14 at 16:56

my execv() function not working in linux ubuntu

2 Answers2