string :file-expand-name ( string $FILEPATH )

For given file name, returns the full path to the file - drive letter (on Windows), all directories, and the filename.
String type (ASCII/UTF-8) matches the argument type.

# :file-expand-name example.
:set &i i0
!while :lt $i :param-cnt
    :writeln $i s'. Name: ' :param-str $i
    :writeln $i s'. Path: ' :file-expand-name :param-str $i
    :add &i i1
!done