realpath(3)

1REALPATH(3)                Linux Programmer's Manual               REALPATH(3)
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NAME

6       realpath - return the canonicalized absolute pathname
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SYNOPSIS

9       #include <limits.h>
10       #include <stdlib.h>
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12       char *realpath(const char *path, char *resolved_path);
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DESCRIPTION

15       realpath() expands all symbolic links and resolves references to '/./',
16       '/../' and extra '/' characters in the null terminated string named  by
17       path  and  stores  the canonicalized absolute pathname in the buffer of
18       size PATH_MAX named by resolved_path.  The resulting path will have  no
19       symbolic link, '/./' or '/../' components.
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RETURN VALUE

22       If   there   is   no   error,  realpath()  returns  a  pointer  to  the
23       resolved_path.
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25       Otherwise it returns a NULL pointer, and  the  contents  of  the  array
26       resolved_path  are undefined. The global variable errno is set to indi‐
27       cate the error.
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ERRORS

30       EACCES Read or search permission was denied for a component of the path
31              prefix.
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33       EINVAL Either  path or resolved_path is NULL. (In libc5 this would just
34              cause a segfault.)  But, see NOTES below.
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36       EIO    An I/O error occurred while reading from the file system.
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38       ELOOP  Too many symbolic links  were  encountered  in  translating  the
39              pathname.
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41       ENAMETOOLONG
42              A  component  of  a pathname exceeded NAME_MAX characters, or an
43              entire pathname exceeded PATH_MAX characters.
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45       ENOENT The named file does not exist.
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47       ENOTDIR
48              A component of the path prefix is not a directory.
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NOTES

51       The glibc implementation of realpath() provides a  non-standard  exten‐
52       sion.  If resolved_path is specified as NULL, then realpath() uses mal‐
53       loc(3) to allocate a buffer  of  up  to  PATH_MAX  bytes  to  hold  the
54       resolved  pathname,  and  returns a pointer to this buffer.  The caller
55       should deallocate this buffer using free(3).
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BUGS

58       Avoid using this function. It is broken by design since  (unless  using
59       the  non-standard  resolved_path == NULL  feature)  it is impossible to
60       determine  a  suitable  size  for  the  output  buffer,  resolved_path.
61       According  to  POSIX  a  buffer of size PATH_MAX suffices, but PATH_MAX
62       need not be a defined constant, and may have to be obtained using path‐
63       conf().   And  asking pathconf() does not really help, since on the one
64       hand POSIX warns that the result of pathconf() may be huge and  unsuit‐
65       able  for mallocing memory. And on the other hand pathconf() may return
66       -1 to signify that PATH_MAX is not bounded.
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68       The libc4 and libc5 implementation contains a buffer overflow (fixed in
69       libc-5.4.13).   Thus,  set-user-ID  programs  like mount need a private
70       version.
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HISTORY

73       The realpath() function first appeared in 4.4BSD, contributed  by  Jan-
74       Simon Pendry.  In Linux this function appears in libc 4.5.21.
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CONFORMING TO

77       4.4BSD, POSIX.1-2001.
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79       In  4.4BSD  and  Solaris the limit on the pathname length is MAXPATHLEN
80       (found in <sys/param.h>).  SUSv2 prescribes PATH_MAX and  NAME_MAX,  as
81       found  in <limits.h> or provided by the pathconf() function.  A typical
82       source fragment would be
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84              #ifdef PATH_MAX
85                path_max = PATH_MAX;
86              #else
87                path_max = pathconf (path, _PC_PATH_MAX);
88                if (path_max <= 0)
89                  path_max = 4096;
90              #endif
91       (But see the BUGS section.)
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93       The 4.4BSD, Linux and SUSv2 versions always return  an  absolute  path‐
94       name.  Solaris may return a relative pathname when the path argument is
95       relative.  The prototype of realpath() is given in <unistd.h> in  libc4
96       and libc5, but in <stdlib.h> everywhere else.
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