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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(): _BSD_SOURCE || _XOPEN_SOURCE >= 500 DESCRIPTION realpath() expands all symbolic links and resolves references to '/./', '/../' and extra '/' characters in the null terminated string named by path and stores the canonicalized absolute pathname in the buffer of size PATH_MAX named by resolved_path. The resulting path will have no symbolic link, '/./' or '/../' components. RETURN VALUE If there is no error, realpath() returns a pointer to the resolved_path. Otherwise it returns a NULL pointer, and the contents of the array resolved_path are undefined. The global variable errno is set to indi- cate the error. ERRORS EACCES Read or search permission was denied for a component of the path prefix. EINVAL Either path or resolved_path is NULL. (In libc5 this would just cause a segfault.) But, see NOTES below. EIO An I/O error occurred while reading from the file system. 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. ENOTDIR A component of the path prefix is not a directory. VERSIONS On Linux this function appeared in libc 4.5.21. CONFORMING TO 4.4BSD, POSIX.1-2001. 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.) The 4.4BSD, Linux and SUSv2 versions always return an absolute path- name. Solaris may return a relative pathname when the path argument is relative. The prototype of realpath() is given in <unistd.h> in libc4 and libc5, but in <stdlib.h> everywhere else. NOTES The glibc implementation of realpath() provides a non-standard exten- sion. If resolved_path is specified as NULL, then realpath() uses mal- loc(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). BUGS Avoid using this function. It is broken by design since (unless using the non-standard resolved_path == NULL feature) it is impossible to determine a suitable size for the output buffer, resolved_path. According to POSIX a buffer of size PATH_MAX suffices, but PATH_MAX need not be a defined constant, and may have to be obtained using path- conf(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 unsuit- able for mallocing memory. And on the other hand pathconf(3) may return -1 to signify that PATH_MAX is not bounded. The libc4 and libc5 implementation contains a buffer overflow (fixed in libc-5.4.13). Thus, set-user-ID programs like mount need a private version. SEE ALSO readlink(2), canonicalize_file_name(3), getcwd(3), pathconf(3), sysconf(3) 2007-07-26 REALPATH(3)