readlink(2) [mojave man page]

READLINK(2)						      BSD System Calls Manual						       READLINK(2)

NAME

     readlink, readlinkat -- read value of a symbolic link

SYNOPSIS

     #include <unistd.h>

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

     ssize_t
     readlinkat(int fd, const char *restrict path, char *restrict buf, size_t bufsize);

DESCRIPTION

     readlink() places the contents of the symbolic link path in the buffer buf, which has size bufsize.  Readlink does not append a NUL character
     to buf.

     The readlinkat() system call is equivalent to readlink() except in the case where path specifies a relative path.	In this case the symbolic
     link whose content is read relative to the directory associated with the file descriptor fd instead of the current working directory.  If
     readlinkat() is passed the special value AT_FDCWD in the fd parameter, the current working directory is used and the behavior is identical to
     a call to readlink().

RETURN VALUES

     The call returns the count of characters placed in the buffer if it succeeds, or a -1 if an error occurs, placing the error code in the
     global variable errno.

ERRORS

     readlink() will fail if:

     [EACCES]		Search permission is denied for a component of the path prefix.

     [EFAULT]		Buf extends outside the process's allocated address space.

     [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 are encountered in translating the pathname.  This is taken to be indicative of a looping symbolic
			link.

     [ENAMETOOLONG]	A component of a pathname exceeded {NAME_MAX} characters, or an entire path name (possibly expanded by a symbolic link)
			exceeded {PATH_MAX} characters.

     [ENOENT]		The named file does not exist.

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

     In addition to the errors returned by the readlink(), the readlinkat() may fail if:

     [EBADF]		The path argument does not specify an absolute path and the fd argument is neither AT_FDCWD nor a valid file descriptor
			open for searching.

     [ENOTDIR]		The path argument is not an absolute path and fd is neither AT_FDCWD nor a file descriptor associated with a directory.

LEGACY SYNOPSIS

     #include <unistd.h>

     int
     readlink(const char *path, char *buf, int bufsize);

     The function type and the type of bufsize have changed.

SEE ALSO

     lstat(2), stat(2), symlink(2), compat(5), symlink(7)

STANDARDS

     The readlinkat() system call is expected to conform to POSIX.1-2008 .

HISTORY

     The readlink() function call appeared in 4.2BSD.  The readlinkat() system call appeared in OS X 10.10

4.2 Berkeley Distribution					   June 4, 1993 					 4.2 Berkeley Distribution

READLINK(3P)						     POSIX Programmer's Manual						      READLINK(3P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       readlink, readlinkat -- read the contents of a symbolic link

SYNOPSIS

       #include <unistd.h>

       ssize_t readlink(const char *restrict path, char *restrict buf,
	   size_t bufsize);
       ssize_t readlinkat(int fd, const char *restrict path,
	   char *restrict buf, size_t bufsize);

DESCRIPTION

       The readlink() function shall place the contents of the symbolic link referred to by path in the buffer buf which has size bufsize.  If the
       number of bytes in the symbolic link is less than bufsize, the contents of the remainder of buf are unspecified. If the buf argument is not
       large enough to contain the link content, the first bufsize bytes shall be placed in buf.

       If the value of bufsize is greater than {SSIZE_MAX}, the result is implementation-defined.

       Upon successful completion, readlink() shall mark for update the last data access timestamp of the symbolic link.

       The readlinkat() function shall be equivalent to the readlink() function except in the case where path specifies a relative path.  In  this
       case  the  symbolic  link  whose content is read is relative to the directory associated with the file descriptor fd instead of the current
       working directory. If the file descriptor was opened without O_SEARCH, the function shall check whether directory  searches  are  permitted
       using  the  current permissions of the directory underlying the file descriptor. If the file descriptor was opened with O_SEARCH, the func-
       tion shall not perform the check.

       If readlinkat() is passed the special value AT_FDCWD in the fd parameter, the current working directory shall  be  used	and  the  behavior
       shall be identical to a call to readlink().

RETURN VALUE

       Upon successful completion, these functions shall return the count of bytes placed in the buffer. Otherwise, these functions shall return a
       value of -1, leave the buffer unchanged, and set errno to indicate the error.

ERRORS

       These functions shall fail if:

       EACCES Search permission is denied for a component of the path prefix of path.

       EINVAL The path argument names a file that is not a symbolic link.

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

       ELOOP  A loop exists in symbolic links encountered during resolution of the path argument.

       ENAMETOOLONG
	      The length of a component of a pathname is longer than {NAME_MAX}.

       ENOENT A component of path does not name an existing file or path is an empty string.

       ENOTDIR
	      A component of the path prefix names an existing file that is neither a directory nor a symbolic link to a directory,  or  the  path
	      argument	contains  at  least  one non-<slash> character and ends with one or more trailing <slash> characters and the last pathname
	      component names an existing file that is neither a directory nor a symbolic link to a directory.

       The readlinkat() function shall fail if:

       EACCES fd was not opened with O_SEARCH and the permissions of the directory underlying fd do not permit directory searches.

       EBADF  The path argument does not specify an absolute path and the fd argument is neither AT_FDCWD nor a valid  file  descriptor  open  for
	      reading or searching.

       ENOTDIR
	      The path argument is not an absolute path and fd is a file descriptor associated with a non-directory file.

       These functions may fail if:

       ELOOP  More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.

       ENAMETOOLONG
	      The length of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic link produced an intermediate result with a length
	      that exceeds {PATH_MAX}.

       The following sections are informative.

EXAMPLES

   Reading the Name of a Symbolic Link
       The following example shows how to read the name of a symbolic link named /modules/pass1.

	   #include <unistd.h>

	   char buf[1024];
	   ssize_t len;
	   ...
	   if ((len = readlink("/modules/pass1", buf, sizeof(buf)-1)) != -1)
	       buf[len] = '';

APPLICATION USAGE

       Conforming applications should not assume that the returned contents of the symbolic link are null-terminated.

RATIONALE

       The type associated with bufsiz is a size_t in order to be consistent with both the ISO C standard  and	the  definition  of  read().   The
       behavior  specified  for readlink() when bufsiz is zero represents historical practice. For this case, the standard developers considered a
       change whereby readlink() would return the number of non-null bytes contained in the symbolic link with the buffer buf remaining unchanged;
       however, since the stat structure member st_size value can be used to determine the size of buffer necessary to contain the contents of the
       symbolic link as returned by readlink(), this proposal was rejected, and the historical practice retained.

       The purpose of the readlinkat() function is to read the content of symbolic links in directories other than the current	working  directory
       without	exposure  to  race  conditions.  Any part of the path of a file could be changed in parallel to a call to readlink(), resulting in
       unspecified behavior. By opening a file descriptor for the target directory and using the readlinkat() function it can be  guaranteed  that
       the symbolic link read is located relative to the desired directory.

FUTURE DIRECTIONS

       None.

SEE ALSO

       fstatat(), symlink()

       The Base Definitions volume of POSIX.1-2008, <unistd.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C)  2013  by	the  Institute	of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE
/The Open Group						       2013							      READLINK(3P)