realpath

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

NAME
       realpath - return the canonicalized absolute pathname

SYNOPSIS
       #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():
           _XOPEN_SOURCE >= 500
               || /* Glibc since 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _BSD_SOURCE

DESCRIPTION
       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 path-
       name 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 path-
       name, and returns a pointer to this buffer.  The caller should  deallo-
       cate this buffer using free(3).

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

       Otherwise, it returns NULL, the contents of the array resolved_path are
       undefined, and errno is set to indicate the error.

ERRORS
       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.

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

       ENOENT The named file does not exist.

       ENOMEM Out of memory.

       ENOTDIR
              A component of the path prefix is not a directory.

ATTRIBUTES
       For   an   explanation   of   the  terms  used  in  this  section,  see
       attributes(7).

       +-----------+---------------+---------+
       |Interface  | Attribute     | Value   |
       +-----------+---------------+---------+
       |realpath() | Thread safety | MT-Safe |
       +-----------+---------------+---------+
CONFORMING TO
       4.4BSD, POSIX.1-2001.

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

NOTES
       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 provided by the pathconf(3) function.  A typical
       source fragment would be

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

       (But see the BUGS section.)

   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.

BUGS
       The POSIX.1-2001 standard version of this function is broken by design,
       since it is impossible to determine a suitable size for the output buf-
       fer,  resolved_path.   According  to  POSIX.1-2001  a  buffer  of  size
       PATH_MAX suffices, but PATH_MAX need not be a defined constant, 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 avoided.

SEE ALSO
       realpath(1),  readlink(2),  canonicalize_file_name(3), getcwd(3), path-
       conf(3), sysconf(3)

COLOPHON
       This page is part of release 4.15 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.

                                  2017-09-15                       REALPATH(3)
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