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by root (Scribe)
on Dec 23, 1999 at 00:52 UTC ( #1217=perlfunc: print w/replies, xml ) Need Help??


See the current Perl documentation for IO::Handle.

Here is our local, out-dated (pre-5.6) version:

IO::Handle - supply object methods for I/O handles

    use IO::Handle;

    $fh = new IO::Handle;
    if ($fh->fdopen(fileno(STDIN),"r")) {
        print $fh->getline;

    $fh = new IO::Handle;
    if ($fh->fdopen(fil

IO::Handle is the base class for all other IO handle classes. It is not intended that objects of IO::Handle would be created directly, but instead IO::Handle is inherited from by several other classes in the IO hierarchy.

If you are reading this documentation, looking for a replacement for the FileHandle package, then I suggest you read the documentation for IO::File

A IO::Handle object is a reference to a symbol (see the Symbol package)


new ()

Creates a new IO::Handle object.

new_from_fd ( FD, MODE )

Creates a IO::Handle like new does. It requires two parameters, which are passed to the method fdopen; if the fdopen fails, the object is destroyed. Otherwise, it is returned to the caller.


See perlfunc for complete descriptions of each of the following supported IO::Handle methods, which are just front ends for the corresponding built-in functions:


See perlvar for complete descriptions of each of the following supported IO::Handle methods:


Furthermore, for doing normal I/O you might need these:

$fh->fdopen ( FD, MODE )

fdopen is like an ordinary open except that its first parameter is not a filename but rather a file handle name, a IO::Handle object, or a file descriptor number.


Returns true if the object is currently a valid file descriptor.


This works like <$fh> described in perlop except that it's more readable and can be safely called in an array context but still returns just one line.


This works like <$fh> when called in an array context to read all the remaining lines in a file, except that it's more readable. It will also croak() if accidentally called in a scalar context.

$fh->ungetc ( ORD )

Pushes a character with the given ordinal value back onto the given handle's input stream.

$fh->write ( BUF, LEN [, OFFSET }\] )

This write is like write found in C, that is it is the opposite of read. The wrapper for the perl write function is called format_write.


Flush the given handle's buffer.


Returns a true value if the given handle has experienced any errors since it was opened or since the last call to clearerr.


Clear the given handle's error indicator.

If the C functions setbuf() and/or setvbuf() are available, then IO::Handle::setbuf and IO::Handle::setvbuf set the buffering policy for an IO::Handle. The calling sequences for the Perl functions are the same as their C counterparts--including the constants _IOFBF, _IOLBF, and _IONBF for setvbuf()--except that the buffer parameter specifies a scalar variable to use as a buffer. WARNING: A variable used as a buffer by setbuf or setvbuf must not be modified in any way until the IO::Handle is closed or setbuf or setvbuf is called again, or memory corruption may result! Note that you need to import the constants _IOFBF, _IOLBF, and _IONBF explicitly.

Lastly, there is a special method for working under -T and setuid/gid scripts:


Marks the object as taint-clean, and as such data read from it will also be considered taint-clean. Note that this is a very trusting action to take, and appropriate consideration for the data source and potential vulnerability should be kept in mind.


A IO::Handle object is a GLOB reference. Some modules that inherit from IO::Handle may want to keep object related variables in the hash table part of the GLOB. In an attempt to prevent modules trampling on each other I propose the that any such module should prefix its variables with its own name separated by _'s. For example the IO::Socket module keeps a timeout variable in 'io_socket_timeout'.


perlfunc, perlop, File


Due to backwards compatibility, all filehandles resemble objects of class IO::Handle, or actually classes derived from that class. They actually aren't. Which means you can't derive your own class from IO::Handle and inherit those methods.


Derived from by Graham Barr <>

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[LanX]: OH
[LanX]: you are talking about signatures?
[GotToBTru]: yes, it turns out I am
[LanX]: http://perldoc. html#Prototypes
[GotToBTru]: that page, strangely enough, never mentions that construct
[LanX]: ; is for optional prototypes
[LanX]: & is codeblock @ array
[GotToBTru]: okay, that is there in the text, not in literal use in any of the examples
[GotToBTru]: the text suggest it is redundant before @
[LanX]: propably ... I also notice new stuff

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