realpath - return the canonicalized absolute pathname

       For an explanation of the terms used in this section, see attributes(7).
       ┌─────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                                                                   │ Attribute     │ Value   │
       ├─────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │ realpath()                                                                  │ Thread safety │ MT-Safe │
       └─────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

       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 avoided.

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).

EACCES Read or search permission was denied for a component of the path prefix.

       EINVALpath is NULL.  (Before glibc 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.

       4.4BSD, POSIX.1-2001, Solaris.

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

       (But see the BUGS section.)

       Standard C library (libc, -lc)

       realpath - return the canonicalized absolute pathname

       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.

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

Linux man-pages 6.9.1                              2024-05-02                                        realpath(3)

       POSIX.1-2008.

#include<limits.h>#include<stdlib.h>char*realpath(constchar*restrictpath,char*restrictresolved_path);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       realpath():
           _XOPEN_SOURCE >= 500
               || /* glibc >= 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _BSD_SOURCE

GNUextensions
       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.