realpath(3)

1realpath(3)                Library Functions Manual                realpath(3)
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NAME

6       realpath - return the canonicalized absolute pathname
7

LIBRARY

9       Standard C library (libc, -lc)
10

SYNOPSIS

12       #include <limits.h>
13       #include <stdlib.h>
14
15       char *realpath(const char *restrict path,
16                      char *restrict resolved_path);
17
18   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
19
20       realpath():
21           _XOPEN_SOURCE >= 500
22               || /* glibc >= 2.19: */ _DEFAULT_SOURCE
23               || /* glibc <= 2.19: */ _BSD_SOURCE
24

DESCRIPTION

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

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

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

69       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
70       tributes(7).
71
72       ┌────────────────────────────────────────────┬───────────────┬─────────┐
73       │Interface                                   │ Attribute     │ Value   │
74       ├────────────────────────────────────────────┼───────────────┼─────────┤
75       │realpath()                                  │ Thread safety │ MT-Safe │
76       └────────────────────────────────────────────┴───────────────┴─────────┘
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VERSIONS

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

85       POSIX.1-2008.
86

HISTORY

88       4.4BSD, POSIX.1-2001, Solaris.
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90       POSIX.1-2001 says  that  the  behavior  if  resolved_path  is  NULL  is
91       implementation-defined.   POSIX.1-2008 specifies the behavior described
92       in this page.
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94       In 4.4BSD and Solaris, the limit on the pathname length  is  MAXPATHLEN
95       (found  in  <sys/param.h>).  SUSv2 prescribes PATH_MAX and NAME_MAX, as
96       found in <limits.h> or provided by the pathconf(3) function.  A typical
97       source fragment would be
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99           #ifdef PATH_MAX
100             path_max = PATH_MAX;
101           #else
102             path_max = pathconf(path, _PC_PATH_MAX);
103             if (path_max <= 0)
104               path_max = 4096;
105           #endif
106
107       (But see the BUGS section.)
108

BUGS

110       The POSIX.1-2001 standard version of this function is broken by design,
111       since it is impossible to determine a suitable size for the output buf‐
112       fer,  resolved_path.   According  to  POSIX.1-2001  a  buffer  of  size
113       PATH_MAX suffices, but PATH_MAX need not be a defined constant, and may
114       have to be obtained using pathconf(3).  And asking pathconf(3) does not
115       really help, since, on the one hand POSIX  warns  that  the  result  of
116       pathconf(3) may be huge and unsuitable for mallocing memory, and on the
117       other hand pathconf(3) may return -1 to signify that  PATH_MAX  is  not
118       bounded.    The  resolved_path == NULL  feature,  not  standardized  in
119       POSIX.1-2001, but standardized  in  POSIX.1-2008,  allows  this  design
120       problem to be avoided.
121