Creates a unique temporary filename in the specified directory. If the directory does not exist, tempnam() may generate a filename in the system's temporary directory.
Prior to PHP 4.0.6, the behaviour of the tempnam() function was system dependent. On Windows the TMP environment variable will override the dir parameter, on Linux the TMPDIR environment variable has precedence, while SVR4 will always use your dir parameter if the directory it points to exists. Consult your system documentation on the tempnam(3) function if in doubt.
Returns the new temporary filename, or the NULL string on failure.
Note: This function's behavior changed in 4.0.3. The temporary file is also created to avoid a race condition where the file might appear in the filesystem between the time the string was generated and before the the script gets around to creating the file.
See also tmpfile().