Write a byte in the file.

writeByte( stream , position )

stream is a file previously opened by the open command.
position represent the position where the byte will be wrote to, this position is measured in number of byte from file beginning.

open "myfile.txt" for output as 1
writebyte( 1,asc("s") )
writebyte( 1,asc("d") )
writebyte( 1,asc("l") )
writebyte( 1,asc("B") )
writebyte( 1,asc("a") )
writebyte( 1,asc("s") )
writebyte( 1,asc("i") )
writebyte( 1,asc("c") )
writebyte( 1,13 )
close 1

See also readByte() command.