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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 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.

       The following sections are informative.

EXAMPLES

   Generating an Absolute Pathname
       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 ...
           }

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
       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.

FUTURE DIRECTIONS

       None.

SEE ALSO

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

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

COPYRIGHT

       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 .