view_symlink.c

/* view_symlink.c

   Demonstrate the use of readlink() and realpath() to read and display
   the contents of a symbolic link.
*/
#include <sys/stat.h>
#include <limits.h>             /* For definition of PATH_MAX */
#include "tlpi_hdr.h"

#define BUF_SIZE PATH_MAX
int
main(int argc, char *argv[])
{
    struct stat statbuf;
    char buf[BUF_SIZE];
    ssize_t numBytes;

    if (argc != 2 || strcmp(argv[1], "--help") == 0)
        usageErr("%s pathname\n", argv[0]);

    /* User lstat() to check whether the supplied pathname is
       a symbolic link. Alternatively, we could have checked to
       whether readlink() failed with EINVAL. */

    if (lstat(argv[1], &statbuf) == -1)
        errExit("lstat");

    if (!S_ISLNK(statbuf.st_mode))
        fatal("%s is not a symbolic link", argv[1]);

    numBytes = readlink(argv[1], buf, BUF_SIZE - 1);
    if (numBytes == -1)
        errExit("readlink");
    buf[numBytes] = '\0';                       /* Add terminating null byte */
    printf("readlink: %s --> %s\n", argv[1], buf);

    if (realpath(argv[1], buf) == NULL)
        errExit("realpath");
    printf("realpath: %s --> %s\n", argv[1], buf);

    exit(EXIT_SUCCESS);
}