IO::Wrap(3pm) User Contributed Perl Documentation IO::Wrap(3pm)
NAME
IO::Wrap - Wrap raw filehandles in the IO::Handle interface
SYNOPSIS
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
$wrap_fh->print("Hey there!");
DESCRIPTION
Let's say you want to write some code which does I/O, but you don't want
to force the caller to provide you with a FileHandle or IO::Handle
object. You want them to be able to say:
do_stuff(\*STDOUT);
do_stuff('STDERR');
do_stuff($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.
FUNCTIONS
IO::Wrap makes the following functions available.
wraphandle
# 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 IO::Wrap constructor
method.
METHODS
IO::Wrap implements the following methods.
close
$fh->close();
The "close" method will attempt to close the system file descriptor. For
a more complete description, read "close" in perlfunc.
fileno
my $int = $fh->fileno();
The "fileno" method returns the file descriptor for the wrapped
filehandle. See "fileno" in perlfunc for more information.
getline
my $data = $fh->getline();
The "getline" method mimics the function by the same name in IO::Handle.
It's like calling "my $data = <$fh>;" but only in scalar context.
getlines
my @data = $fh->getlines();
The "getlines" method mimics the function by the same name in
IO::Handle. It's like calling "my @data = <$fh>;" but only in list
context. Calling this method in scalar context will result in a croak.
new
# 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 IO::Wrap object instance.
A raw filehandle glob, like "\*STDOUT" can also be wrapped, returning an
IO::Wrawp object instance.
A blessed FileHandle object can also be wrapped. This is a special case
where an IO::Wrap 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 IO::Handle
interface can be passed in. In this case, you just get back that object.
In other words, we only wrap it into an IO::Wrap object when what you've
supplied doesn't already conform to the IO::Handle interface.
If you get back an IO::Wrap object, it will obey a basic subset of the
"IO::" interface. It will do so with object methods, not operators.
CAVEATS
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.
print
$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 "print" in
perlfunc.
read
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 read 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 "read" in perlfunc for more information.
seek
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 "seek" in perlfunc for more
information.
tell
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 "tell" in perlfunc for
more information.
AUTHOR
Eryq (eryq@zeegee.com). President, ZeeGee Software Inc
(http://www.zeegee.com).
CONTRIBUTORS
Dianne Skoll (dfs@roaringpenguin.com).
COPYRIGHT & LICENSE
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.
perl v5.38.2 2024-07-31 IO::Wrap(3pm)
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