Advanced Perl Programming

Tying Filehandles

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.

Table 9-4. tie and Filehandles

When you say:	Perl translates it to:
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.