Tied filehandles call a user-defined object whenever you read from or write to a filehandle, as shown in Table 9.4. Note that the tie statement takes a typeglob, not a bareword.

tie *FH, 'Foo', 'a','b'

$obj = Foo-->TIEHANDLE('a','b'),

<FH>

$obj-->READLINE();

read (FH, $buf, $len, $offset)
sysread (FH, $buf, $len, $offset)

$obj->READ($buf, $len, $offset)

getc(FH)

$obj->GETC()

print FH "I do"; #No comma after FH

$obj-->PRINT("I do");

untie *FH;

$obj-->DESTROY();

This method can be used to simulate a file or process with a test driver or to monitor access to a filehandle for silently logging a conversation (like the tee(1) command). Tk, which we will study in detail in Chapter 14, supports ties to let you redirect I/O to its text widget. We will look at a small example of this feature when we study that widget.