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NAME

       readlink - read value of a symbolic link

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 file system.

       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 as ssize_t, as (newly) required in
       POSIX.1-2001.

       Using  a  statically  sized  buffer  might  not  provide enough room for the symbolic link
       contents.  The required size for the buffer can be obtained from  the  stat.st_size  value
       returned  by  a  call  to  lstat(2)  on the link.  However, the number of bytes written by
       readlink() should be checked to make sure that the size  of  the  symbolic  link  did  not
       increase  between  the  calls.   Dynamically  allocating  the  buffer  for readlink() also
       addresses a common portability problem when using PATH_MAX for the buffer  size,  as  this
       constant is not guaranteed to be defined per POSIX if the system does not have such limit.

EXAMPLE

       The  following  program  allocates  the  buffer  needed by readlink() dynamically 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 < 0) {
               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[sb.st_size] = '\0';

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

           exit(EXIT_SUCCESS);
       }

SEE ALSO

       readlink(1), lstat(2), readlinkat(2), stat(2), symlink(2), path_resolution(7), symlink(7)

COLOPHON

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