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IO::Handle(3)	       Perl Programmers Reference Guide		 IO::Handle(3)

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

	   use IO::Handle;

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

	   $io = new IO::Handle;
	   if ($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.

       new ()
	   Creates a new "IO::Handle" object.

       new_from_fd ( FD, MODE )
	   Creates an "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

       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

	   $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:

       $io->fdopen ( FD, MODE )
	   "fdopen" is like an ordinary "open" except that its first parameter
	   is not a filename but rather a file handle name, an IO::Handle
	   object, or a file descriptor number.	 (For the documentation of the
	   "open" method, see IO::File.)

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

	   This works like <$io> described in "I/O Operators" in perlop except
	   that it's more readable and can be safely called in a list context
	   but still returns just one line.  If used as the conditional
	   +within a "while" or C-style "for" loop, however, you will need to
	   +emulate the functionality of <$io> with "defined($_ =

	   This works like <$io> when called in a list 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.

       $io->ungetc ( ORD )
	   Pushes a character with the given ordinal value back onto the given
	   handle's input stream.  Only one character of pushback per handle
	   is guaranteed.

       $io->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

	   Returns a true value if the given handle has experienced any errors
	   since it was opened or since the last call to "clearerr", or if the
	   handle is invalid. It only returns false for a valid handle with no
	   outstanding errors.

	   Clear the given handle's error indicator. Returns -1 if the handle
	   is invalid, 0 otherwise.

	   "sync" synchronizes a file's in-memory state	 with  that  on the
	   physical medium. "sync" does not operate at the perlio api level,
	   but operates on the file descriptor (similar to sysread, sysseek
	   and systell). This means that any data held at the perlio api level
	   will not be synchronized. To synchronize data that is buffered at
	   the perlio api level you must use the flush method. "sync" is not
	   implemented on all platforms. Returns "0 but true" on success,
	   "undef" on error, "undef" for an invalid handle. See fsync(3c).

	   "flush" causes perl to flush any buffered data at the perlio api
	   level.  Any unread data in the buffer will be discarded, and any
	   unwritten data will be written to the underlying file descriptor.
	   Returns "0 but true" on success, "undef" on error.

       $io->printflush ( ARGS )
	   Turns on autoflush, print ARGS and then restores the autoflush
	   status of the "IO::Handle" object. Returns the return value from

       $io->blocking ( [ BOOL ] )
	   If called with an argument "blocking" will turn on non-blocking IO
	   if "BOOL" is false, and turn it off if "BOOL" is true.

	   "blocking" will return the value of the previous setting, or the
	   current setting if "BOOL" is not given.

	   If an error occurs "blocking" will return undef and $! will be set.

       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

	   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. Returns 0 on
	   success, -1 if setting the taint-clean flag failed. (eg invalid

       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 <>

perl v5.10.1			  2009-06-23			 IO::Handle(3)

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