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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;

	   $io = IO::Handle->new();
	   if ($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.

       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($_ = $io->getline)".

	   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 somewhat like "write" found in C, in	that it	is the
	   opposite of read. The wrapper for the perl "write" function is
	   called "format_write". However, whilst the C	"write"	function
	   returns the number of bytes written,	this "write" function simply
	   returns true	if successful (like "print"). A	more C-like "write" is
	   "syswrite" (see above).

	   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 v5.32.0			  2020-06-14			 IO::Handle(3)


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