IO::Wrap - Wrap raw filehandles in the IO::Handle interface
use strict;
use warnings;
use IO::Wrap;
# this is a fairly senseless use case as IO::Handle already does this.
my $wrap_fh = IO::Wrap->new(\*STDIN);
my $line = $wrap_fh->getline();
# Do stuff with any kind of filehandle (including a bare globref), or
# any kind of blessed object that responds to a print() message.
# already have a globref? a FileHandle? a scalar filehandle name?
$wrap_fh = IO::Wrap->new($some_unknown_thing);
# At this point, we know we have an IO::Handle-like object! YAY
$wrap_fh->print("Hey there!");
You can also do this using a convenience wrapper function
use strict;
use warnings;
use IO::Wrap qw(wraphandle);
# this is a fairly senseless use case as IO::Handle already does this.
my $wrap_fh = wraphandle(\*STDIN);
my $line = $wrap_fh->getline();
# Do stuff with any kind of filehandle (including a bare globref), or
# any kind of blessed object that responds to a print() message.
# already have a globref? a FileHandle? a scalar filehandle name?
$wrap_fh = wraphandle($some_unknown_thing);
# At this point, we know we have an IO::Handle-like object! YAY
$wrap_fh->print("Hey there!");
Let's say you want to write some code which does I/O, but you don't
want to force the caller to provide you with a FileHandle or the IO::Handle manpage
object. You want them to be able to say:
do_stuff(\*STDOUT);
do_stuff('STDERR');
do_stuff($some_FileHandle_object);
do_stuff($some_IO_Handle_object);
And even:
do_stuff($any_object_with_a_print_method);
Sure, one way to do it is to force the caller to use tiehandle().
But that puts the burden on them. Another way to do it is to
use IO::Wrap.
Clearly, when wrapping a raw external filehandle (like \*STDOUT),
I didn't want to close the file descriptor when the wrapper object is
destroyed; the user might not appreciate that! Hence, there's no
DESTROY method in this class.
When wrapping a FileHandle object, however, I believe that Perl will
invoke the FileHandle::DESTROY when the last reference goes away,
so in that case, the filehandle is closed if the wrapped FileHandle
really was the last reference to it.
the IO::Wrap manpage makes the following functions available.
# wrap a filehandle glob
my $fh = wraphandle(\*STDIN);
# wrap a raw filehandle glob by name
$fh = wraphandle('STDIN');
# wrap a handle in an object
$fh = wraphandle('Class::HANDLE');
# wrap a blessed FileHandle object
use FileHandle;
my $fho = FileHandle->new("/tmp/foo.txt", "r");
$fh = wraphandle($fho);
# wrap any other blessed object that shares IO::Handle's interface
$fh = wraphandle($some_object);
This function is simply a wrapper to the new in the IO::Wrap manpage constructor method.
the IO::Wrap manpage implements the following methods.
$fh->close();
The close method will attempt to close the system file descriptor. For a
more complete description, read perlfunc/close.
my $int = $fh->fileno();
The fileno method returns the file descriptor for the wrapped filehandle.
See perlfunc/fileno for more information.
my $data = $fh->getline();
The getline method mimics the function by the same name in the IO::Handle manpage.
It's like calling my $data = <$fh>; but only in scalar context.
my @data = $fh->getlines();
The getlines method mimics the function by the same name in the IO::Handle manpage.
It's like calling my @data = <$fh>; but only in list context. Calling
this method in scalar context will result in a croak.
# wrap a filehandle glob
my $fh = IO::Wrap->new(\*STDIN);
# wrap a raw filehandle glob by name
$fh = IO::Wrap->new('STDIN');
# wrap a handle in an object
$fh = IO::Wrap->new('Class::HANDLE');
# wrap a blessed FileHandle object
use FileHandle;
my $fho = FileHandle->new("/tmp/foo.txt", "r");
$fh = IO::Wrap->new($fho);
# wrap any other blessed object that shares IO::Handle's interface
$fh = IO::Wrap->new($some_object);
The new constructor method takes in a single argument and decides to wrap
it or not it based on what it seems to be.
A raw scalar file handle name, like "STDOUT" or "Class::HANDLE" can be
wrapped, returning an the IO::Wrap manpage object instance.
A raw filehandle glob, like \*STDOUT can also be wrapped, returning an
the IO::Wrawp manpage object instance.
A blessed FileHandle object can also be wrapped. This is a special case
where an the IO::Wrap manpage object instance will only be returned in the case that
your FileHandle object doesn't support the read method.
Also, any other kind of blessed object that conforms to the
the IO::Handle manpage interface can be passed in. In this case, you just get back
that object.
In other words, we only wrap it into an the IO::Wrap manpage object when what you've
supplied doesn't already conform to the the IO::Handle manpage interface.
If you get back an the IO::Wrap manpage object, it will obey a basic subset of
the IO:: interface. It will do so with object methods, not operators.
This module does not allow you to wrap filehandle names which are given
as strings that lack the package they were opened in. That is, if a user
opens FOO in package Foo, they must pass it to you either as \*FOO
or as "Foo::FOO". However, "STDIN" and friends will work just fine.
$fh->print("Some string");
$fh->print("more", " than one", " string");
The print method will attempt to print a string or list of strings to the
filehandle. For a more complete description, read
perlfunc/print.
my $buffer;
# try to read 30 chars into the buffer starting at the
# current cursor position.
my $num_chars_read = $fh->read($buffer, 30);
The the read manpage method attempts to read a number of characters, starting at the
filehandle's current cursor position. It returns the number of characters
actually read. See perlfunc/read for more information.
use Fcntl qw(:seek); # import the SEEK_CUR, SEEK_SET, SEEK_END constants
# seek to the position in bytes
$fh->seek(0, SEEK_SET);
# seek to the position in bytes from the current position
$fh->seek(22, SEEK_CUR);
# seek to the EOF plus bytes
$fh->seek(0, SEEK_END);
The seek method will attempt to set the cursor to a given position in bytes
for the wrapped file handle. See perlfunc/seek for more information.
my $bytes = $fh->tell();
The tell method will attempt to return the current position of the cursor
in bytes for the wrapped file handle. See perlfunc/tell for more
information.
Eryq (eryq@zeegee.com).
President, ZeeGee Software Inc (http://www.zeegee.com).
Dianne Skoll (dfs@roaringpenguin.com).
Copyright (c) 1997 Erik (Eryq) Dorfman, ZeeGee Software, Inc. All rights reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
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