1REALPATH(3)                Linux Programmer's Manual               REALPATH(3)
2
3
4

NAME

6       realpath - return the canonicalized absolute pathname
7

SYNOPSIS

9       #include <limits.h>
10       #include <stdlib.h>
11
12       char *realpath(const char *restrict path,
13                      char *restrict resolved_path);
14
15   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
16
17       realpath():
18           _XOPEN_SOURCE >= 500
19               || /* Glibc since 2.19: */ _DEFAULT_SOURCE
20               || /* Glibc <= 2.19: */ _BSD_SOURCE
21

DESCRIPTION

23       realpath()  expands  all symbolic links and resolves references to /./,
24       /../ and extra '/' characters in the null-terminated  string  named  by
25       path to produce a canonicalized absolute pathname.  The resulting path‐
26       name is stored as a null-terminated string, up to a maximum of PATH_MAX
27       bytes,  in  the buffer pointed to by resolved_path.  The resulting path
28       will have no symbolic link, /./ or /../ components.
29
30       If resolved_path is specified as NULL, then realpath()  uses  malloc(3)
31       to allocate a buffer of up to PATH_MAX bytes to hold the resolved path‐
32       name, and returns a pointer to this buffer.  The caller should  deallo‐
33       cate this buffer using free(3).
34

RETURN VALUE

36       If  there  is  no  error,  realpath()  returns  a  pointer  to  the re‐
37       solved_path.
38
39       Otherwise, it returns NULL, the contents of the array resolved_path are
40       undefined, and errno is set to indicate the error.
41

ERRORS

43       EACCES Read or search permission was denied for a component of the path
44              prefix.
45
46       EINVAL path is NULL.  (In glibc versions before 2.3, this error is also
47              returned if resolved_path is NULL.)
48
49       EIO    An I/O error occurred while reading from the filesystem.
50
51       ELOOP  Too  many  symbolic  links  were  encountered in translating the
52              pathname.
53
54       ENAMETOOLONG
55              A component of a pathname exceeded NAME_MAX  characters,  or  an
56              entire pathname exceeded PATH_MAX characters.
57
58       ENOENT The named file does not exist.
59
60       ENOMEM Out of memory.
61
62       ENOTDIR
63              A component of the path prefix is not a directory.
64

ATTRIBUTES

66       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
67       tributes(7).
68
69       ┌────────────────────────────────────────────┬───────────────┬─────────┐
70Interface                                   Attribute     Value   
71       ├────────────────────────────────────────────┼───────────────┼─────────┤
72realpath()                                  │ Thread safety │ MT-Safe │
73       └────────────────────────────────────────────┴───────────────┴─────────┘
74

CONFORMING TO

76       4.4BSD, POSIX.1-2001.
77
78       POSIX.1-2001 says that the behavior if resolved_path is NULL is  imple‐
79       mentation-defined.   POSIX.1-2008  specifies  the behavior described in
80       this page.
81

NOTES

83       In 4.4BSD and Solaris, the limit on the pathname length  is  MAXPATHLEN
84       (found  in  <sys/param.h>).  SUSv2 prescribes PATH_MAX and NAME_MAX, as
85       found in <limits.h> or provided by the pathconf(3) function.  A typical
86       source fragment would be
87
88           #ifdef PATH_MAX
89             path_max = PATH_MAX;
90           #else
91             path_max = pathconf(path, _PC_PATH_MAX);
92             if (path_max <= 0)
93               path_max = 4096;
94           #endif
95
96       (But see the BUGS section.)
97
98   GNU extensions
99       If the call fails with either EACCES or ENOENT and resolved_path is not
100       NULL, then the prefix of path that is not readable or does not exist is
101       returned in resolved_path.
102

BUGS

104       The POSIX.1-2001 standard version of this function is broken by design,
105       since it is impossible to determine a suitable size for the output buf‐
106       fer,  resolved_path.   According  to  POSIX.1-2001  a  buffer  of  size
107       PATH_MAX suffices, but PATH_MAX need not be a defined constant, and may
108       have to be obtained using pathconf(3).  And asking pathconf(3) does not
109       really help, since, on the one hand POSIX  warns  that  the  result  of
110       pathconf(3) may be huge and unsuitable for mallocing memory, and on the
111       other hand pathconf(3) may return -1 to signify that  PATH_MAX  is  not
112       bounded.    The  resolved_path == NULL  feature,  not  standardized  in
113       POSIX.1-2001, but standardized  in  POSIX.1-2008,  allows  this  design
114       problem to be avoided.
115

SEE ALSO

117       realpath(1),  readlink(2),  canonicalize_file_name(3), getcwd(3), path‐
118       conf(3), sysconf(3)
119

COLOPHON

121       This page is part of release 5.12 of the Linux  man-pages  project.   A
122       description  of  the project, information about reporting bugs, and the
123       latest    version    of    this    page,    can     be     found     at
124       https://www.kernel.org/doc/man-pages/.
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128                                  2021-03-22                       REALPATH(3)
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