5 IO::Handle - supply object methods for I/O handles
12 if ($io->fdopen(fileno(STDIN),"r")) {
18 if ($io->fdopen(fileno(STDOUT),"w")) {
19 $io->print("Some text\n");
22 # setvbuf is not available by default on Perls 5.8.0 and later.
23 use IO::Handle '_IOLBF';
24 $io->setvbuf($buffer_var, _IOLBF, 1024);
26 undef $io; # automatically closes the file if it's open
32 C<IO::Handle> is the base class for all other IO handle classes. It is
33 not intended that objects of C<IO::Handle> would be created directly,
34 but instead C<IO::Handle> is inherited from by several other classes
37 If you are reading this documentation, looking for a replacement for
38 the C<FileHandle> package, then I suggest you read the documentation
47 Creates a new C<IO::Handle> object.
49 =item new_from_fd ( FD, MODE )
51 Creates an C<IO::Handle> like C<new> does.
52 It requires two parameters, which are passed to the method C<fdopen>;
53 if the fdopen fails, the object is destroyed. Otherwise, it is returned
60 See L<perlfunc> for complete descriptions of each of the following
61 supported C<IO::Handle> methods, which are just front ends for the
62 corresponding built-in functions:
67 $io->format_write( [FORMAT_NAME] )
69 $io->read ( BUF, LEN, [OFFSET] )
71 $io->printf ( FMT, [ARGS] )
73 $io->sysread ( BUF, LEN, [OFFSET] )
74 $io->syswrite ( BUF, [LEN, [OFFSET]] )
77 See L<perlvar> for complete descriptions of each of the following
78 supported C<IO::Handle> methods. All of them return the previous
79 value of the attribute and takes an optional single argument that when
80 given will set the value. If no argument is given the previous value
81 is unchanged (except for $io->autoflush will actually turn ON
82 autoflush by default).
84 $io->autoflush ( [BOOL] ) $|
85 $io->format_page_number( [NUM] ) $%
86 $io->format_lines_per_page( [NUM] ) $=
87 $io->format_lines_left( [NUM] ) $-
88 $io->format_name( [STR] ) $~
89 $io->format_top_name( [STR] ) $^
90 $io->input_line_number( [NUM]) $.
92 The following methods are not supported on a per-filehandle basis.
94 IO::Handle->format_line_break_characters( [STR] ) $:
95 IO::Handle->format_formfeed( [STR]) $^L
96 IO::Handle->output_field_separator( [STR] ) $,
97 IO::Handle->output_record_separator( [STR] ) $\
99 IO::Handle->input_record_separator( [STR] ) $/
101 Furthermore, for doing normal I/O you might need these:
105 =item $io->fdopen ( FD, MODE )
107 C<fdopen> is like an ordinary C<open> except that its first parameter
108 is not a filename but rather a file handle name, an IO::Handle object,
109 or a file descriptor number.
113 Returns true if the object is currently a valid file descriptor, false
118 This works like <$io> described in L<perlop/"I/O Operators">
119 except that it's more readable and can be safely called in a
120 list context but still returns just one line.
124 This works like <$io> when called in a list context to read all
125 the remaining lines in a file, except that it's more readable.
126 It will also croak() if accidentally called in a scalar context.
128 =item $io->ungetc ( ORD )
130 Pushes a character with the given ordinal value back onto the given
131 handle's input stream. Only one character of pushback per handle is
134 =item $io->write ( BUF, LEN [, OFFSET ] )
136 This C<write> is like C<write> found in C, that is it is the
137 opposite of read. The wrapper for the perl C<write> function is
138 called C<format_write>.
142 Returns a true value if the given handle has experienced any errors
143 since it was opened or since the last call to C<clearerr>, or if the
144 handle is invalid. It only returns false for a valid handle with no
149 Clear the given handle's error indicator. Returns -1 if the handle is
150 invalid, 0 otherwise.
154 C<sync> synchronizes a file's in-memory state with that on the
155 physical medium. C<sync> does not operate at the perlio api level, but
156 operates on the file descriptor (similar to sysread, sysseek and
157 systell). This means that any data held at the perlio api level will not
158 be synchronized. To synchronize data that is buffered at the perlio api
159 level you must use the flush method. C<sync> is not implemented on all
160 platforms. Returns "0 but true" on success, C<undef> on error, C<undef>
161 for an invalid handle. See L<fsync(3c)>.
165 C<flush> causes perl to flush any buffered data at the perlio api level.
166 Any unread data in the buffer will be discarded, and any unwritten data
167 will be written to the underlying file descriptor. Returns "0 but true"
168 on success, C<undef> on error.
170 =item $io->printflush ( ARGS )
172 Turns on autoflush, print ARGS and then restores the autoflush status of the
173 C<IO::Handle> object. Returns the return value from print.
175 =item $io->blocking ( [ BOOL ] )
177 If called with an argument C<blocking> will turn on non-blocking IO if
178 C<BOOL> is false, and turn it off if C<BOOL> is true.
180 C<blocking> will return the value of the previous setting, or the
181 current setting if C<BOOL> is not given.
183 If an error occurs C<blocking> will return undef and C<$!> will be set.
188 If the C functions setbuf() and/or setvbuf() are available, then
189 C<IO::Handle::setbuf> and C<IO::Handle::setvbuf> set the buffering
190 policy for an IO::Handle. The calling sequences for the Perl functions
191 are the same as their C counterparts--including the constants C<_IOFBF>,
192 C<_IOLBF>, and C<_IONBF> for setvbuf()--except that the buffer parameter
193 specifies a scalar variable to use as a buffer. You should only
194 change the buffer before any I/O, or immediately after calling flush.
196 WARNING: The IO::Handle::setvbuf() is not available by default on
197 Perls 5.8.0 and later because setvbuf() is rather specific to using
198 the stdio library, while Perl prefers the new perlio subsystem instead.
200 WARNING: A variable used as a buffer by C<setbuf> or C<setvbuf> B<must not
201 be modified> in any way until the IO::Handle is closed or C<setbuf> or
202 C<setvbuf> is called again, or memory corruption may result! Remember that
203 the order of global destruction is undefined, so even if your buffer
204 variable remains in scope until program termination, it may be undefined
205 before the file IO::Handle is closed. Note that you need to import the
206 constants C<_IOFBF>, C<_IOLBF>, and C<_IONBF> explicitly. Like C, setbuf
207 returns nothing. setvbuf returns "0 but true", on success, C<undef> on
210 Lastly, there is a special method for working under B<-T> and setuid/gid
217 Marks the object as taint-clean, and as such data read from it will also
218 be considered taint-clean. Note that this is a very trusting action to
219 take, and appropriate consideration for the data source and potential
220 vulnerability should be kept in mind. Returns 0 on success, -1 if setting
221 the taint-clean flag failed. (eg invalid handle)
227 An C<IO::Handle> object is a reference to a symbol/GLOB reference (see
228 the C<Symbol> package). Some modules that
229 inherit from C<IO::Handle> may want to keep object related variables
230 in the hash table part of the GLOB. In an attempt to prevent modules
231 trampling on each other I propose the that any such module should prefix
232 its variables with its own name separated by _'s. For example the IO::Socket
233 module keeps a C<timeout> variable in 'io_socket_timeout'.
238 L<perlop/"I/O Operators">,
243 Due to backwards compatibility, all filehandles resemble objects
244 of class C<IO::Handle>, or actually classes derived from that class.
245 They actually aren't. Which means you can't derive your own
246 class from C<IO::Handle> and inherit those methods.
250 Derived from FileHandle.pm by Graham Barr E<lt>F<gbarr@pobox.com>E<gt>
256 our($VERSION, @EXPORT_OK, @ISA);
260 use IO (); # Load the XS module
266 $VERSION = eval $VERSION;
270 output_field_separator
271 output_record_separator
272 input_record_separator
275 format_lines_per_page
279 format_line_break_characters
299 ################################################
300 ## Constructors, destructors.
304 my $class = ref($_[0]) || $_[0] || "IO::Handle";
305 @_ == 1 or croak "usage: new $class";
311 my $class = ref($_[0]) || $_[0] || "IO::Handle";
312 @_ == 3 or croak "usage: new_from_fd $class FD, MODE";
315 IO::Handle::fdopen($io, @_)
321 # There is no need for DESTROY to do anything, because when the
322 # last reference to an IO object is gone, Perl automatically
323 # closes its associated files (if any). However, to avoid any
324 # attempts to autoload DESTROY, we here define it to do nothing.
329 ################################################
333 sub _open_mode_string {
335 $mode =~ /^\+?(<|>>?)$/
336 or $mode =~ s/^r(\+?)$/$1</
337 or $mode =~ s/^w(\+?)$/$1>/
338 or $mode =~ s/^a(\+?)$/$1>>/
339 or croak "IO::Handle: bad open mode: $mode";
344 @_ == 3 or croak 'usage: $io->fdopen(FD, MODE)';
345 my ($io, $fd, $mode) = @_;
348 if (ref($fd) && "".$fd =~ /GLOB\(/o) {
349 # It's a glob reference; Alias it as we cannot get name of anon GLOBs
350 my $n = qualify(*GLOB);
353 } elsif ($fd =~ m#^\d+$#) {
354 # It's an FD number; prefix with "=".
358 open($io, _open_mode_string($mode) . '&' . $fd)
363 @_ == 1 or croak 'usage: $io->close()';
369 ################################################
370 ## Normal I/O functions.
377 @_ == 1 or croak 'usage: $io->opened()';
378 defined fileno($_[0]);
382 @_ == 1 or croak 'usage: $io->fileno()';
387 @_ == 1 or croak 'usage: $io->getc()';
392 @_ == 1 or croak 'usage: $io->eof()';
397 @_ or croak 'usage: $io->print(ARGS)';
403 @_ >= 2 or croak 'usage: $io->printf(FMT,[ARGS])';
409 @_ == 1 or croak 'usage: $io->getline()';
411 return scalar <$this>;
414 *gets = \&getline; # deprecated
417 @_ == 1 or croak 'usage: $io->getlines()';
419 croak 'Can\'t call $io->getlines in a scalar context, use $io->getline';
425 @_ == 2 or croak 'usage: $io->truncate(LEN)';
426 truncate($_[0], $_[1]);
430 @_ == 3 || @_ == 4 or croak 'usage: $io->read(BUF, LEN [, OFFSET])';
431 read($_[0], $_[1], $_[2], $_[3] || 0);
435 @_ == 3 || @_ == 4 or croak 'usage: $io->sysread(BUF, LEN [, OFFSET])';
436 sysread($_[0], $_[1], $_[2], $_[3] || 0);
440 @_ >= 2 && @_ <= 4 or croak 'usage: $io->write(BUF [, LEN [, OFFSET]])';
442 $_[2] = length($_[1]) unless defined $_[2];
443 print { $_[0] } substr($_[1], $_[3] || 0, $_[2]);
447 @_ >= 2 && @_ <= 4 or croak 'usage: $io->syswrite(BUF [, LEN [, OFFSET]])';
448 if (defined($_[2])) {
449 syswrite($_[0], $_[1], $_[2], $_[3] || 0);
451 syswrite($_[0], $_[1]);
456 @_ == 1 or croak 'usage: $io->stat()';
460 ################################################
461 ## State modification functions.
465 my $old = new SelectSaver qualify($_[0], caller);
467 $| = @_ > 1 ? $_[1] : 1;
471 sub output_field_separator {
472 carp "output_field_separator is not supported on a per-handle basis"
475 $, = $_[1] if @_ > 1;
479 sub output_record_separator {
480 carp "output_record_separator is not supported on a per-handle basis"
483 $\ = $_[1] if @_ > 1;
487 sub input_record_separator {
488 carp "input_record_separator is not supported on a per-handle basis"
491 $/ = $_[1] if @_ > 1;
495 sub input_line_number {
497 () = tell qualify($_[0], caller) if ref($_[0]);
499 $. = $_[1] if @_ > 1;
503 sub format_page_number {
505 $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
507 $% = $_[1] if @_ > 1;
511 sub format_lines_per_page {
513 $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
515 $= = $_[1] if @_ > 1;
519 sub format_lines_left {
521 $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
523 $- = $_[1] if @_ > 1;
529 $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
531 $~ = qualify($_[1], caller) if @_ > 1;
535 sub format_top_name {
537 $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
539 $^ = qualify($_[1], caller) if @_ > 1;
543 sub format_line_break_characters {
544 carp "format_line_break_characters is not supported on a per-handle basis"
547 $: = $_[1] if @_ > 1;
551 sub format_formfeed {
552 carp "format_formfeed is not supported on a per-handle basis"
555 $^L = $_[1] if @_ > 1;
564 formline($picture, @_);
569 @_ < 3 || croak 'usage: $io->write( [FORMAT_NAME] )';
572 my $oldfmt = $io->format_name($fmt);
574 $io->format_name($oldfmt);
582 @_ == 3 || croak 'usage: $io->fcntl( OP, VALUE );';
584 return fcntl($io, $op, $_[2]);
589 @_ == 3 || croak 'usage: $io->ioctl( OP, VALUE );';
591 return ioctl($io, $op, $_[2]);
594 # this sub is for compatability with older releases of IO that used
595 # a sub called constant to detemine if a constant existed -- GMB
597 # The SEEK_* and _IO?BF constants were the only constants at that time
598 # any new code should just chech defined(&CONSTANT_NAME)
603 (($name =~ /^(SEEK_(SET|CUR|END)|_IO[FLN]BF)$/) && defined &{$name})
604 ? &{$name}() : undef;
608 # so that flush.pl can be deprecated
613 $old = new SelectSaver qualify($io, caller) if ref($io);