realpath

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 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 .



IEEE/The Open Group                   2017                          REALPATH(3P)