dim info$( 50, 50)    '   NB pre-dimension before calling file-exists
                      '        needed for file-exists function
open "test.dat" for output as #1    'create file
    for i = 1 to 10000
        #1 chr$( int( 256 *rnd( 1)));
    next
close #1

call truncateFile, "test.dat", 5000

wait

sub truncateFile fn$, length
    if fileExists( DefaultDir$, fn$) =0 then notice "No such file": exit sub
    open fn$ for input as #i
        file$ =input$( #i, lof( #i))
        if len( file$) <length then notice "Too short": close #i: exit sub
        file$ =left$( file$, length)
    close #i
    open "test.dat" for output as #o
        #o file$
    close #o
end sub

function fileExists( path$, filename$)
  files path$, filename$, info$()
  fileExists =val( info$( 0, 0))  'non zero is true
end function

end