readlink


SYNOPSIS
       #include <unistd.h>

       ssize_t readlink(const char *path, char *buf, size_t bufsiz);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       readlink():
           _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
           _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED ||
           _POSIX_C_SOURCE >= 200112L

DESCRIPTION
       readlink()  places the contents of the symbolic link path in the buffer
       buf, which has size bufsiz.  readlink() does not append a null byte  to
       buf.  It will truncate the contents (to a length of bufsiz characters),
       in case the buffer is too small to hold all of the contents.

RETURN VALUE
       On success, readlink() returns the number of bytes placed in  buf.   On
       error, -1 is returned and errno is set to indicate the error.

ERRORS
       EACCES Search  permission is denied for a component of the path prefix.
              (See also path_resolution(7).)

       EFAULT buf extends outside the process's allocated address space.

       EINVAL bufsiz is not positive.

       EINVAL The named file is not a symbolic link.

       EIO    An I/O error occurred while reading from the filesystem.

       ELOOP  Too many symbolic links  were  encountered  in  translating  the
              pathname.

       ENAMETOOLONG
              A pathname, or a component of a pathname, was too long.

       ENOENT The named file does not exist.

       ENOMEM Insufficient kernel memory was available.

       ENOTDIR
              A component of the path prefix is not a directory.

CONFORMING TO
       4.4BSD (readlink() first appeared in 4.2BSD), POSIX.1-2001.

NOTES
       In  versions of glibc up to and including glibc 2.4, the return type of
       readlink() was declared as int.  Nowadays, the return type is  declared

EXAMPLE
       The following program allocates the buffer needed by readlink() dynami-
       cally from the information provided by lstat(), making sure there's  no
       race condition between the calls.

       #include <sys/types.h>
       #include <sys/stat.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>

       int
       main(int argc, char *argv[])
       {
           struct stat sb;
           char *linkname;
           ssize_t r;

           if (argc != 2) {
               fprintf(stderr, "Usage: %s <pathname>\n", argv[0]);
               exit(EXIT_FAILURE);
           }

           if (lstat(argv[1], &sb) == -1) {
               perror("lstat");
               exit(EXIT_FAILURE);
           }

           linkname = malloc(sb.st_size + 1);
           if (linkname == NULL) {
               fprintf(stderr, "insufficient memory\n");
               exit(EXIT_FAILURE);
           }

           r = readlink(argv[1], linkname, sb.st_size + 1);

           if (r == -1) {
               perror("lstat");
               exit(EXIT_FAILURE);
           }

           if (r > sb.st_size) {
               fprintf(stderr, "symlink increased in size "
                               "between lstat() and readlink()\n");
               exit(EXIT_FAILURE);
           }

           linkname[r] = '\0';

           printf("'%s' points to '%s'\n", argv[1], linkname);

           exit(EXIT_SUCCESS);
       }
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