Know-How für Ihr Projekt

Perl Documentation


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


use IO::Handle;
$io = IO::Handle->new();
if ($io->fdopen(fileno(STDIN),"r")) {
    print $io->getline;
$io = IO::Handle->new();
if ($io->fdopen(fileno(STDOUT),"w")) {
    $io->print("Some text\n");
# setvbuf is not available by default on Perls 5.8.0 and later.
use IO::Handle '_IOLBF';
$io->setvbuf($buffer_var, _IOLBF, 1024);
undef $io;       # automatically closes the file if it's open
autoflush STDOUT 1;


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 too.



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:

$io->fcntl( FUNCTION, SCALAR )
$io->format_write( [FORMAT_NAME] )
$io->ioctl( FUNCTION, SCALAR )
$io->read ( BUF, LEN, [OFFSET] )
$io->print ( ARGS )
$io->printf ( FMT, [ARGS] )
$io->say ( ARGS )
$io->sysread ( BUF, LEN, [OFFSET] )
$io->syswrite ( BUF, [LEN, [OFFSET]] )
$io->truncate ( LEN )

See perlvar for complete descriptions of each of the following supported IO::Handle methods. All of them return the previous value of the attribute and takes an optional single argument that when given will set the value. If no argument is given the previous value is unchanged (except for $io->autoflush will actually turn ON autoflush by default).

$io->autoflush ( [BOOL] )                         $|
$io->format_page_number( [NUM] )                  $%
$io->format_lines_per_page( [NUM] )               $=
$io->format_lines_left( [NUM] )                   $-
$io->format_name( [STR] )                         $~
$io->format_top_name( [STR] )                     $^
$io->input_line_number( [NUM])                    $.

The following methods are not supported on a per-filehandle basis.

IO::Handle->format_line_break_characters( [STR] ) $:
IO::Handle->format_formfeed( [STR])               $^L
IO::Handle->output_field_separator( [STR] )       $,
IO::Handle->output_record_separator( [STR] )      $\
IO::Handle->input_record_separator( [STR] )       $/

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

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. You should only change the buffer before any I/O, or immediately after calling flush.

WARNING: The IO::Handle::setvbuf() is not available by default on Perls 5.8.0 and later because setvbuf() is rather specific to using the stdio library, while Perl prefers the new perlio subsystem instead.

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! Remember that the order of global destruction is undefined, so even if your buffer variable remains in scope until program termination, it may be undefined before the file IO::Handle is closed. Note that you need to import the constants _IOFBF, _IOLBF, and _IONBF explicitly. Like C, setbuf returns nothing. setvbuf returns "0 but true", on success, undef on failure.

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


An IO::Handle object is a reference to a symbol/GLOB reference (see the Symbol package). 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, "I/O Operators" in perlop, IO::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 <>