$which(<file> [<dir>[:<dir> …]])

The <file> argument is a dword, which is different from most functions.

This function returns the full pathname of the specified filename. The function will search the client's current LOAD_PATH for the file. In addition, a list of colon-delimited directories may be specified, which will be searched if the file is not found in the LOAD_PATH.

This function tries to find the location of a particular file. This makes it suitable for LOAD and STUB commands, allowing a file to be loaded, even if its exact location is not known.

the canonical path of the file, or nothing if it isn't found

$which(some_file)           shows full path of file
$which(does_not_exist)      returns nothing, file dies not exist
$which(some_file /bin)      search in /bin for some_file too