Question

Program : List all C files in the current folder using execlp() system call:

#include <stdio.h>
#include <unistd.h>

int main()
{
    printf("Before Execl\n");
    execlp("ls","ls","*.c",NULL); // this should print all c files in the current folder.
    return 0;
}

Program output:

Before Execl
ls: cannot access *.c: No such file or directory

Whenever I use ‘*‘ in the search pattern, I am getting a similar kind of error. Please suggest some appropriate solution.

Answer 1

If you want shell metacharacters expanded, invoke the shell to expand them, thus:

execlp("sh", "sh", "-c", "ls *.c", (char *)0);
fprintf(stderr, "Failed to exec /bin/sh (%d %s)\n", errno, strerror(errno));
exit(EXIT_FAILURE);

Note that if execl() or any of the exec* functions returned, it failed. You don’t need to test its status; it failed. You should not then do exit(0); (or return 0; in the main() function) as that indicates success. It is courteous to include an error message outlining what went wrong, and the message should be written to stderr, not stdout — as shown.

You can do the metacharacter expansion yourself; there are functions in the POSIX library to assist (such as glob()). But it is a whole heap simpler to let the shell do it.

(I’ve revised the code above to use execlp() to conform to the requirements of the question. If I were doing this unconstrained, I’d probably use execl() and specify "/bin/sh" as the first argument instead.)