# FILNAM > [HTML Version](filnamsbr.htm) **xcall FILNAM, ch, filename** FILNAM returns _filename_ when only the file channel is known. This is frequently useful in conjunction with error trapping, where the trapping routine identifies the file only by channel. **Parameters** _ch_ ([Num](num.htm.md)) \[in\] the channel that the file is open on _filename_ ([String](string.htm.md)) \[out\] will return the filename (as specified in the open statement) corresponding to the specified file channel. If no file is open on that channel, _filename_ returns a null string.