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REALPATH(3) Library Functions Manual REALPATH(3)

returns the canonicalized absolute pathname

#include <limits.h>
#include <stdlib.h>

char *
realpath(const char *pathname, char *resolved);

The realpath() function resolves all symbolic links, extra “/” characters and references to /./ and /../ in pathname, and copies the resulting absolute pathname into the memory referenced by resolved. The resolved argument must refer to a buffer capable of storing at least PATH_MAX characters, or be NULL.

The realpath() function will resolve both absolute and relative paths and return the absolute pathname corresponding to pathname. All but the last component of pathname must exist when realpath() is called.

The realpath() function returns resolved on success. If resolved is NULL and no error occurred, then realpath() returns a NUL-terminated string in a newly allocated buffer. If an error occurs, realpath() returns NULL and the contents of resolved are undefined.

The function realpath() may fail and set the external variable errno for any of the errors specified for the library functions lstat(2), readlink(2), and getcwd(3).

readlink(1), getcwd(3)

The realpath() function conforms to IEEE Std 1003.1-2008 (“POSIX.1”).

The realpath() function call first appeared in 4.4BSD.

This implementation of realpath() differs slightly from the Solaris implementation. The 4.4BSD version always returns absolute pathnames, whereas the Solaris implementation will, under certain circumstances, return a relative resolved when given a relative pathname.
January 20, 2014 OpenBSD-current