SUB opener (a$)
    WHEN EXCEPTION IN
         OPEN #1: NAME f$
         PRINT f$; " exists"
    USE
         PRINT f$; " not exists"
    END WHEN
    CLOSE #1
END SUB

LET f$ = "input.txt"
CALL opener (f$)
LET f$ = "\input.txt"
CALL opener (f$)
LET f$ = "docs\nul"
CALL opener (f$)
LET f$ = "\docs\nul"
CALL opener (f$)

LET f$ = "empty.tru"
CALL opener (f$)
LET f$ = "`Abdu'l-Bahá.txt"
CALL opener (f$)
END