#open FILEHANDLE,MODE,EXPR #open FILEHANDLE,MODE,EXPR,LIST #open FILEHANDLE,MODE,REFERENCE #open FILEHANDLE,EXPR #open FILEHANDLE Associates an internal FILEHANDLE with the external file specified by EXPR. That filehandle will subsequently allow you to perform I/O operations on that file, such as reading from it or writing to it. Instead of a filename, you may specify an external command (plus an