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Linux 2.6 - man page for realpath (linux section 3)

REALPATH(3)			    Linux Programmer's Manual			      REALPATH(3)

       realpath - return the canonicalized absolute pathname

       #include <limits.h>
       #include <stdlib.h>

       char *realpath(const char *path, char *resolved_path);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):


       realpath()  expands  all symbolic links and resolves references to /./, /../ and extra '/'
       characters in the null-terminated string named by path to produce a canonicalized absolute
       pathname.   The	resulting pathname is stored as a null-terminated string, up to a maximum
       of PATH_MAX bytes, in the buffer pointed to by resolved_path.   The  resulting  path  will
       have no symbolic link, /./ or /../ components.

       If resolved_path is specified as NULL, then realpath() uses malloc(3) to allocate a buffer
       of up to PATH_MAX bytes to hold the resolved pathname, and returns a pointer to this  buf-
       fer.  The caller should deallocate this buffer using free(3).

       If there is no error, realpath() returns a pointer to the resolved_path.

       Otherwise,  it  returns	a NULL pointer, the contents of the array resolved_path are unde-
       fined, and errno is set to indicate the error.

       EACCES Read or search permission was denied for a component of the path prefix.

       EINVAL path is NULL.  (In glibc versions before	2.3,  this  error  is  also  returned  if
	      resolved_path is NULL.)

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

       ELOOP  Too many symbolic links were encountered in translating the pathname.

	      A  component  of	a  pathname  exceeded  NAME_MAX characters, or an entire pathname
	      exceeded PATH_MAX characters.

       ENOENT The named file does not exist.

	      A component of the path prefix is not a directory.

       On Linux, this function appeared in libc 4.5.21.

       4.4BSD, POSIX.1-2001.

       POSIX.1-2001 says that the behavior if resolved_path is	NULL  is  implementation-defined.
       POSIX.1-2008 specifies the behavior described in this page.

       In  4.4BSD  and	Solaris,  the  limit  on  the  pathname  length  is  MAXPATHLEN (found in
       <sys/param.h>).	SUSv2 prescribes PATH_MAX and NAME_MAX, as found in  <limits.h>  or  pro-
       vided by the pathconf(3) function.  A typical source fragment would be

	   #ifdef PATH_MAX
	     path_max = PATH_MAX;
	     path_max = pathconf(path, _PC_PATH_MAX);
	     if (path_max <= 0)
	       path_max = 4096;

       (But see the BUGS section.)

       The  prototype  of realpath() is given in <unistd.h> in libc4 and libc5, but in <stdlib.h>
       everywhere else.

   GNU extensions
       If the call fails with either EACCES or ENOENT and resolved_path is  not  NULL,	then  the
       prefix of path that is not readable or does not exist is returned in resolved_path.

       The POSIX.1-2001 standard version of this function is broken by design, since it is impos-
       sible to determine a suitable size for the output  buffer,  resolved_path.   According  to
       POSIX.1-2001  a	buffer of size PATH_MAX suffices, but PATH_MAX need not be a defined con-
       stant, and may have to be obtained using pathconf(3).  And  asking  pathconf(3)	does  not
       really help, since, on the one hand POSIX warns that the result of pathconf(3) may be huge
       and unsuitable for mallocing memory, and on the other hand pathconf(3) may  return  -1  to
       signify that PATH_MAX is not bounded.  The resolved_path == NULL feature, not standardized
       in POSIX.1-2001, but standardized in  POSIX.1-2008,  allows  this  design  problem  to  be

       The  libc4  and	libc5  implementation contained a buffer overflow (fixed in libc-5.4.13).
       Thus, set-user-ID programs like mount(8) needed a private version.

       readlink(2), canonicalize_file_name(3), getcwd(3), pathconf(3), sysconf(3)

       This page is part of release 3.55 of the Linux man-pages project.  A  description  of  the
       project,     and    information	  about    reporting	bugs,	 can	be    found    at

					    2013-03-15				      REALPATH(3)

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