This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       For functions that allocate memory as if by malloc(), the application should release such memory when  it
       is no longer required by a call to free().  For realpath(), this is the return value.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  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 Standard is the referee  document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/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                                   2017                                      REALPATH(3POSIX)

       The  realpath()  function  shall  derive, from the pathname pointed to by file_name, an absolute pathname
       that resolves to the same directory entry, whose resolution does  not  involve  '.',  '..',  or  symbolic
       links.  If  resolved_name  is a null pointer, the generated pathname shall be stored as a null-terminated
       string in a buffer allocated as if by a call to malloc().  Otherwise,  if  {PATH_MAX}  is  defined  as  a
       constant  in  the  <limits.h>  header,  then  the generated pathname shall be stored as a null-terminated
       string, up to a maximum of {PATH_MAX} bytes, in the buffer pointed to by resolved_name.

       If resolved_name is not a null pointer and {PATH_MAX} is not defined as  a  constant  in  the  <limits.h>
       header, the behavior is undefined.

       The realpath() function shall fail if:

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

       EINVAL The file_name argument is a null pointer.

       EIO    An error occurred while reading from the file system.

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

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

       ENOENT A component of file_name does not name an existing file or file_name points to 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 file_name 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 realpath() function may fail if:

       EACCES The file_name argument does not begin with a <slash> and none  of  the  symbolic  links  (if  any)
              processed  during  pathname  resolution  of  file_name had contents that began with a <slash>, and
              either search permission was denied for the current directory or read  or  search  permission  was
              denied for a directory above the current directory in the file hierarchy.

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

       ENOMEM Insufficient storage space is available.

       Thefollowingsectionsareinformative.

GeneratinganAbsolutePathname
       The following example generates an absolute pathname for the file identified by the symlinkpath argument.
       The generated pathname is stored in the buffer pointed to by actualpath.

           #include <stdlib.h>
           ...
           char *symlinkpath = "/tmp/symlink/file";
           char *actualpath;

           actualpath = realpath(symlinkpath, NULL);
           if (actualpath != NULL)
           {
               ... use actualpath ...

               free(actualpath);
           }
           else
           {
               ... handle error ...
           }

       None.

       realpath — resolve a pathname

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

       Since  realpath()  has  no  length  argument,  if  {PATH_MAX} is not defined as a constant in <limits.h>,
       applications have no way of determining how large a buffer they need to allocate for it  to  be  safe  to
       pass  to realpath().  A {PATH_MAX} value obtained from a prior pathconf() call is out-of-date by the time
       realpath() is called. Hence the only reliable way to use realpath() when {PATH_MAX}  is  not  defined  in
       <limits.h>  is  to pass a null pointer for resolved_name so that realpath() will allocate a buffer of the
       necessary size.

       Upon successful completion, realpath() shall return a pointer to the buffer containing the resolved name.
       Otherwise, realpath() shall return a null pointer and set errno to indicate the error.

       If  the  resolved_name  argument  is  a null pointer, the pointer returned by realpath() can be passed to
       free().

       If the resolved_name argument is not a null pointer and the realpath() function fails,  the  contents  of
       the buffer pointed to by resolved_name are undefined.

fpathconf(), free(), getcwd(), sysconf()

       The Base Definitions volume of POSIX.1‐2017, <limits.h>, <stdlib.h>

       #include <stdlib.h>

       char *realpath(const char *restrict file_name,
           char *restrict resolved_name);