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       realpath - return the canonicalized absolute pathname


       #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)):

           _XOPEN_SOURCE >= 500
               || /* Glibc since 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _BSD_SOURCE


       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 pathname 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 pathname,  and  returns  a  pointer  to  this
       buffer.  The caller should deallocate this buffer using free(3).


       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.


       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.

              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.

              A component of the path prefix is not a directory.


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

       │InterfaceAttributeValue   │
       │realpath() │ Thread safety │ MT-Safe │


       4.4BSD, POSIX.1-2001.

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


       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;
             path_max = pathconf(path, _PC_PATH_MAX);
             if (path_max <= 0)
               path_max = 4096;

       (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.


       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 buffer, 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


       realpath(1), readlink(2), canonicalize_file_name(3), getcwd(3), pathconf(3), sysconf(3)


       This page is part of release 5.10 of the Linux man-pages project.  A  description  of  the
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       found at

                                            2017-09-15                                REALPATH(3)