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REALPATH(3P)               POSIX Programmer's Manual              REALPATH(3P)
PROLOG
       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.
NAME
       realpath -- resolve a pathname
SYNOPSIS
       #include <stdlib.h>
       char *realpath(const char *restrict file_name,
           char *restrict resolved_name);
DESCRIPTION
       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.
RETURN VALUE
       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.
ERRORS
       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 cur-
              rent 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 resolu-
              tion of a symbolic link produced an intermediate result  with  a
              length that exceeds {PATH_MAX}.
       ENOMEM Insufficient storage space is available.
       The following sections are informative.
EXAMPLES
   Generating an Absolute Pathname
       The following example generates an absolute pathname for the file iden-
       tified 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 ...
           }
APPLICATION USAGE
       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.
RATIONALE
       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 reli-
       able 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.
FUTURE DIRECTIONS
       None.
SEE ALSO
       fpathconf(), free(), getcwd(), sysconf()
       The Base Definitions volume of POSIX.1-2008, <limits.h>, <stdlib.h>
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal 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 Standard
       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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                         REALPATH(3P)