1REALPATH(3) Linux Programmer's Manual REALPATH(3)
2
6 realpath - return the canonicalized absolute pathname
7
9 #include <limits.h>
10 #include <stdlib.h>
11 char *realpath(const char *path, char *resolved_path);
13 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
15 realpath(): _BSD_SOURCE || _XOPEN_SOURCE >= 500
17
19 realpath() expands all symbolic links and resolves references to /./,
20 /../ and extra '/' characters in the null-terminated string named by
21 path to produce a canonicalized absolute pathname. The resulting path‐
22 name is stored as a null-terminated string, up to a maximum of PATH_MAX
23 bytes, in the buffer pointed to by resolved_path. The resulting path
24 will have no symbolic link, /./ or /../ components.
25 If resolved_path is specified as NULL, then realpath() uses malloc(3)
27 to allocate a buffer of up to PATH_MAX bytes to hold the resolved path‐
28 name, and returns a pointer to this buffer. The caller should deallo‐
29 cate this buffer using free(3).
30
32 If there is no error, realpath() returns a pointer to the
33 resolved_path.
34 Otherwise it returns a NULL pointer, and the contents of the array
36 resolved_path are undefined, and errno is set to indicate the error.
37
39 EACCES Read or search permission was denied for a component of the path
40 prefix.
41 EINVAL Either path or resolved_path is NULL. (In libc5 this would just
43 cause a segfault.) But, see NOTES below.
44 EIO An I/O error occurred while reading from the file system.
46 ELOOP Too many symbolic links were encountered in translating the
48 pathname.
49 ENAMETOOLONG
51 A component of a pathname exceeded NAME_MAX characters, or an
52 entire pathname exceeded PATH_MAX characters.
53 ENOENT The named file does not exist.
55 ENOTDIR
57 A component of the path prefix is not a directory.
58
60 On Linux this function appeared in libc 4.5.21.
61
63 4.4BSD, POSIX.1-2001.
64 POSIX.1-2001 says that the behavior if resolved_path is NULL is imple‐
66 mentation-defined. POSIX.1-2008 specifies the behavior described in
67 this page.
68
70 In 4.4BSD and Solaris the limit on the pathname length is MAXPATHLEN
71 (found in <sys/param.h>). SUSv2 prescribes PATH_MAX and NAME_MAX, as
72 found in <limits.h> or provided by the pathconf(3) function. A typical
73 source fragment would be
74 #ifdef PATH_MAX
76 path_max = PATH_MAX;
77 #else
78 path_max = pathconf(path, _PC_PATH_MAX);
79 if (path_max <= 0)
80 path_max = 4096;
81 #endif
82 (But see the BUGS section.)
84 The 4.4BSD, Linux and SUSv2 versions always return an absolute path‐
86 name. Solaris may return a relative pathname when the path argument is
87 relative. The prototype of realpath() is given in <unistd.h> in libc4
88 and libc5, but in <stdlib.h> everywhere else.
89
91 The POSIX.1-2001 standard version of this function is broken by design,
92 since it is impossible to determine a suitable size for the output buf‐
93 fer, resolved_path. According to POSIX.1-2001 a buffer of size
94 PATH_MAX suffices, but PATH_MAX need not be a defined constant, and may
95 have to be obtained using pathconf(3). And asking pathconf(3) does not
96 really help, since, on the one hand POSIX warns that the result of
97 pathconf(3) may be huge and unsuitable for mallocing memory, and on the
98 other hand pathconf(3) may return -1 to signify that PATH_MAX is not
99 bounded. The resolved_path == NULL feature, not standardized in
100 POSIX.1-2001, but standardized in POSIX.1-2008, allows this design
101 problem to be avoided.
102 The libc4 and libc5 implementation contains a buffer overflow (fixed in
104 libc-5.4.13). Thus, set-user-ID programs like mount(8) need a private
105 version.
106
108 readlink(2), canonicalize_file_name(3), getcwd(3), pathconf(3),
109 sysconf(3)
110
112 This page is part of release 3.25 of the Linux man-pages project. A
113 description of the project, and information about reporting bugs, can
114 be found at http://www.kernel.org/doc/man-pages/.
115 2009-02-23 REALPATH(3)