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. If used as the conditional
121 +within a C<while> or C-style C<for> loop, however, you will need to
122 +emulate the functionality of <$io> with C<< defined($_ = $io->getline) >>.
126 This works like <$io> when called in a list context to read all
127 the remaining lines in a file, except that it's more readable.
128 It will also croak() if accidentally called in a scalar context.
130 =item $io->ungetc ( ORD )
132 Pushes a character with the given ordinal value back onto the given
133 handle's input stream. Only one character of pushback per handle is
136 =item $io->write ( BUF, LEN [, OFFSET ] )
138 This C<write> is like C<write> found in C, that is it is the
139 opposite of read. The wrapper for the perl C<write> function is
140 called C<format_write>.
144 Returns a true value if the given handle has experienced any errors
145 since it was opened or since the last call to C<clearerr>, or if the
146 handle is invalid. It only returns false for a valid handle with no
151 Clear the given handle's error indicator. Returns -1 if the handle is
152 invalid, 0 otherwise.
156 C<sync> synchronizes a file's in-memory state with that on the
157 physical medium. C<sync> does not operate at the perlio api level, but
158 operates on the file descriptor (similar to sysread, sysseek and
159 systell). This means that any data held at the perlio api level will not
160 be synchronized. To synchronize data that is buffered at the perlio api
161 level you must use the flush method. C<sync> is not implemented on all
162 platforms. Returns "0 but true" on success, C<undef> on error, C<undef>
163 for an invalid handle. See L<fsync(3c)>.
167 C<flush> causes perl to flush any buffered data at the perlio api level.
168 Any unread data in the buffer will be discarded, and any unwritten data
169 will be written to the underlying file descriptor. Returns "0 but true"
170 on success, C<undef> on error.
172 =item $io->printflush ( ARGS )
174 Turns on autoflush, print ARGS and then restores the autoflush status of the
175 C<IO::Handle> object. Returns the return value from print.
177 =item $io->blocking ( [ BOOL ] )
179 If called with an argument C<blocking> will turn on non-blocking IO if
180 C<BOOL> is false, and turn it off if C<BOOL> is true.
182 C<blocking> will return the value of the previous setting, or the
183 current setting if C<BOOL> is not given.
185 If an error occurs C<blocking> will return undef and C<$!> will be set.
190 If the C functions setbuf() and/or setvbuf() are available, then
191 C<IO::Handle::setbuf> and C<IO::Handle::setvbuf> set the buffering
192 policy for an IO::Handle. The calling sequences for the Perl functions
193 are the same as their C counterparts--including the constants C<_IOFBF>,
194 C<_IOLBF>, and C<_IONBF> for setvbuf()--except that the buffer parameter
195 specifies a scalar variable to use as a buffer. You should only
196 change the buffer before any I/O, or immediately after calling flush.
198 WARNING: The IO::Handle::setvbuf() is not available by default on
199 Perls 5.8.0 and later because setvbuf() is rather specific to using
200 the stdio library, while Perl prefers the new perlio subsystem instead.
202 WARNING: A variable used as a buffer by C<setbuf> or C<setvbuf> B<must not
203 be modified> in any way until the IO::Handle is closed or C<setbuf> or
204 C<setvbuf> is called again, or memory corruption may result! Remember that
205 the order of global destruction is undefined, so even if your buffer
206 variable remains in scope until program termination, it may be undefined
207 before the file IO::Handle is closed. Note that you need to import the
208 constants C<_IOFBF>, C<_IOLBF>, and C<_IONBF> explicitly. Like C, setbuf
209 returns nothing. setvbuf returns "0 but true", on success, C<undef> on
212 Lastly, there is a special method for working under B<-T> and setuid/gid
219 Marks the object as taint-clean, and as such data read from it will also
220 be considered taint-clean. Note that this is a very trusting action to
221 take, and appropriate consideration for the data source and potential
222 vulnerability should be kept in mind. Returns 0 on success, -1 if setting
223 the taint-clean flag failed. (eg invalid handle)
229 An C<IO::Handle> object is a reference to a symbol/GLOB reference (see
230 the C<Symbol> package). Some modules that
231 inherit from C<IO::Handle> may want to keep object related variables
232 in the hash table part of the GLOB. In an attempt to prevent modules
233 trampling on each other I propose the that any such module should prefix
234 its variables with its own name separated by _'s. For example the IO::Socket
235 module keeps a C<timeout> variable in 'io_socket_timeout'.
240 L<perlop/"I/O Operators">,
245 Due to backwards compatibility, all filehandles resemble objects
246 of class C<IO::Handle>, or actually classes derived from that class.
247 They actually aren't. Which means you can't derive your own
248 class from C<IO::Handle> and inherit those methods.
252 Derived from FileHandle.pm by Graham Barr E<lt>F<gbarr@pobox.com>E<gt>
258 our($VERSION, @EXPORT_OK, @ISA);
262 use IO (); # Load the XS module
268 $VERSION = eval $VERSION;
272 output_field_separator
273 output_record_separator
274 input_record_separator
277 format_lines_per_page
281 format_line_break_characters
301 ################################################
302 ## Constructors, destructors.
306 my $class = ref($_[0]) || $_[0] || "IO::Handle";
307 @_ == 1 or croak "usage: new $class";
313 my $class = ref($_[0]) || $_[0] || "IO::Handle";
314 @_ == 3 or croak "usage: new_from_fd $class FD, MODE";
317 IO::Handle::fdopen($io, @_)
323 # There is no need for DESTROY to do anything, because when the
324 # last reference to an IO object is gone, Perl automatically
325 # closes its associated files (if any). However, to avoid any
326 # attempts to autoload DESTROY, we here define it to do nothing.
331 ################################################
335 sub _open_mode_string {
337 $mode =~ /^\+?(<|>>?)$/
338 or $mode =~ s/^r(\+?)$/$1</
339 or $mode =~ s/^w(\+?)$/$1>/
340 or $mode =~ s/^a(\+?)$/$1>>/
341 or croak "IO::Handle: bad open mode: $mode";
346 @_ == 3 or croak 'usage: $io->fdopen(FD, MODE)';
347 my ($io, $fd, $mode) = @_;
350 if (ref($fd) && "".$fd =~ /GLOB\(/o) {
351 # It's a glob reference; Alias it as we cannot get name of anon GLOBs
352 my $n = qualify(*GLOB);
355 } elsif ($fd =~ m#^\d+$#) {
356 # It's an FD number; prefix with "=".
360 open($io, _open_mode_string($mode) . '&' . $fd)
365 @_ == 1 or croak 'usage: $io->close()';
371 ################################################
372 ## Normal I/O functions.
379 @_ == 1 or croak 'usage: $io->opened()';
380 defined fileno($_[0]);
384 @_ == 1 or croak 'usage: $io->fileno()';
389 @_ == 1 or croak 'usage: $io->getc()';
394 @_ == 1 or croak 'usage: $io->eof()';
399 @_ or croak 'usage: $io->print(ARGS)';
405 @_ >= 2 or croak 'usage: $io->printf(FMT,[ARGS])';
411 @_ == 1 or croak 'usage: $io->getline()';
413 return scalar <$this>;
416 *gets = \&getline; # deprecated
419 @_ == 1 or croak 'usage: $io->getlines()';
421 croak 'Can\'t call $io->getlines in a scalar context, use $io->getline';
427 @_ == 2 or croak 'usage: $io->truncate(LEN)';
428 truncate($_[0], $_[1]);
432 @_ == 3 || @_ == 4 or croak 'usage: $io->read(BUF, LEN [, OFFSET])';
433 read($_[0], $_[1], $_[2], $_[3] || 0);
437 @_ == 3 || @_ == 4 or croak 'usage: $io->sysread(BUF, LEN [, OFFSET])';
438 sysread($_[0], $_[1], $_[2], $_[3] || 0);
442 @_ >= 2 && @_ <= 4 or croak 'usage: $io->write(BUF [, LEN [, OFFSET]])';
444 $_[2] = length($_[1]) unless defined $_[2];
445 print { $_[0] } substr($_[1], $_[3] || 0, $_[2]);
449 @_ >= 2 && @_ <= 4 or croak 'usage: $io->syswrite(BUF [, LEN [, OFFSET]])';
450 if (defined($_[2])) {
451 syswrite($_[0], $_[1], $_[2], $_[3] || 0);
453 syswrite($_[0], $_[1]);
458 @_ == 1 or croak 'usage: $io->stat()';
462 ################################################
463 ## State modification functions.
467 my $old = new SelectSaver qualify($_[0], caller);
469 $| = @_ > 1 ? $_[1] : 1;
473 sub output_field_separator {
474 carp "output_field_separator is not supported on a per-handle basis"
477 $, = $_[1] if @_ > 1;
481 sub output_record_separator {
482 carp "output_record_separator is not supported on a per-handle basis"
485 $\ = $_[1] if @_ > 1;
489 sub input_record_separator {
490 carp "input_record_separator is not supported on a per-handle basis"
493 $/ = $_[1] if @_ > 1;
497 sub input_line_number {
499 () = tell qualify($_[0], caller) if ref($_[0]);
501 $. = $_[1] if @_ > 1;
505 sub format_page_number {
507 $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
509 $% = $_[1] if @_ > 1;
513 sub format_lines_per_page {
515 $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
517 $= = $_[1] if @_ > 1;
521 sub format_lines_left {
523 $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
525 $- = $_[1] if @_ > 1;
531 $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
533 $~ = qualify($_[1], caller) if @_ > 1;
537 sub format_top_name {
539 $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
541 $^ = qualify($_[1], caller) if @_ > 1;
545 sub format_line_break_characters {
546 carp "format_line_break_characters is not supported on a per-handle basis"
549 $: = $_[1] if @_ > 1;
553 sub format_formfeed {
554 carp "format_formfeed is not supported on a per-handle basis"
557 $^L = $_[1] if @_ > 1;
566 formline($picture, @_);
571 @_ < 3 || croak 'usage: $io->write( [FORMAT_NAME] )';
574 my $oldfmt = $io->format_name($fmt);
576 $io->format_name($oldfmt);
584 @_ == 3 || croak 'usage: $io->fcntl( OP, VALUE );';
586 return fcntl($io, $op, $_[2]);
591 @_ == 3 || croak 'usage: $io->ioctl( OP, VALUE );';
593 return ioctl($io, $op, $_[2]);
596 # this sub is for compatability with older releases of IO that used
597 # a sub called constant to detemine if a constant existed -- GMB
599 # The SEEK_* and _IO?BF constants were the only constants at that time
600 # any new code should just chech defined(&CONSTANT_NAME)
605 (($name =~ /^(SEEK_(SET|CUR|END)|_IO[FLN]BF)$/) && defined &{$name})
606 ? &{$name}() : undef;
610 # so that flush.pl can be deprecated
615 $old = new SelectSaver qualify($io, caller) if ref($io);