Advanced Perl Programming

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9.4 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');
read (FH, $buf, $len, $offset)
sysread (FH, $buf, $len, $offset)
$obj->READ($buf, $len, $offset)
print FH "I do"; #No comma after FH
$obj->PRINT("I do");
untie *FH;

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, User Interfaces with Tk, 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.

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