6 IO::Handle - supply object methods for I/O handles
13 if ($io->fdopen(fileno(STDIN),"r")) {
19 if ($io->fdopen(fileno(STDOUT),"w")) {
20 $io->print("Some text\n");
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 a 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 $io->fdopen ( FD, MODE )
107 C<fdopen> is like an ordinary C<open> except that its first parameter
108 is not a filename but rather a file handle name, a IO::Handle object,
109 or a file descriptor number.
113 Returns true if the object is currently a valid file descriptor, false
118 This works like <$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 on success, -1 on error, -1 for an invalid handle.
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 on success,
168 or a negative value 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: A variable used as a buffer by C<setbuf> or C<setvbuf> B<must not
197 be modified> in any way until the IO::Handle is closed or C<setbuf> or
198 C<setvbuf> is called again, or memory corruption may result! Remember that
199 the order of global destruction is undefined, so even if your buffer
200 variable remains in scope until program termination, it may be undefined
201 before the file IO::Handle is closed. Note that you need to import the
202 constants C<_IOFBF>, C<_IOLBF>, and C<_IONBF> explicitly. Like C, setbuf
203 returns nothing, setvbuf returns 0 on success, -1 on failure.
205 Lastly, there is a special method for working under B<-T> and setuid/gid
212 Marks the object as taint-clean, and as such data read from it will also
213 be considered taint-clean. Note that this is a very trusting action to
214 take, and appropriate consideration for the data source and potential
215 vulnerability should be kept in mind. Returns 0 on success, -1 if setting
216 the taint-clean flag failed. (eg invalid handle)
222 A C<IO::Handle> object is a reference to a symbol/GLOB reference (see
223 the C<Symbol> package). Some modules that
224 inherit from C<IO::Handle> may want to keep object related variables
225 in the hash table part of the GLOB. In an attempt to prevent modules
226 trampling on each other I propose the that any such module should prefix
227 its variables with its own name separated by _'s. For example the IO::Socket
228 module keeps a C<timeout> variable in 'io_socket_timeout'.
233 L<perlop/"I/O Operators">,
238 Due to backwards compatibility, all filehandles resemble objects
239 of class C<IO::Handle>, or actually classes derived from that class.
240 They actually aren't. Which means you can't derive your own
241 class from C<IO::Handle> and inherit those methods.
245 Derived from FileHandle.pm by Graham Barr E<lt>F<gbarr@pobox.com>E<gt>
251 our($VERSION, @EXPORT_OK, @ISA);
255 use IO (); # Load the XS module
264 output_field_separator
265 output_record_separator
266 input_record_separator
269 format_lines_per_page
273 format_line_break_characters
293 ################################################
294 ## Constructors, destructors.
298 my $class = ref($_[0]) || $_[0] || "IO::Handle";
299 @_ == 1 or croak "usage: new $class";
305 my $class = ref($_[0]) || $_[0] || "IO::Handle";
306 @_ == 3 or croak "usage: new_from_fd $class FD, MODE";
309 IO::Handle::fdopen($io, @_)
315 # There is no need for DESTROY to do anything, because when the
316 # last reference to an IO object is gone, Perl automatically
317 # closes its associated files (if any). However, to avoid any
318 # attempts to autoload DESTROY, we here define it to do nothing.
323 ################################################
327 sub _open_mode_string {
329 $mode =~ /^\+?(<|>>?)$/
330 or $mode =~ s/^r(\+?)$/$1</
331 or $mode =~ s/^w(\+?)$/$1>/
332 or $mode =~ s/^a(\+?)$/$1>>/
333 or croak "IO::Handle: bad open mode: $mode";
338 @_ == 3 or croak 'usage: $io->fdopen(FD, MODE)';
339 my ($io, $fd, $mode) = @_;
342 if (ref($fd) && "".$fd =~ /GLOB\(/o) {
343 # It's a glob reference; Alias it as we cannot get name of anon GLOBs
344 my $n = qualify(*GLOB);
347 } elsif ($fd =~ m#^\d+$#) {
348 # It's an FD number; prefix with "=".
352 open($io, _open_mode_string($mode) . '&' . $fd)
357 @_ == 1 or croak 'usage: $io->close()';
363 ################################################
364 ## Normal I/O functions.
371 @_ == 1 or croak 'usage: $io->opened()';
372 defined fileno($_[0]);
376 @_ == 1 or croak 'usage: $io->fileno()';
381 @_ == 1 or croak 'usage: $io->getc()';
386 @_ == 1 or croak 'usage: $io->eof()';
391 @_ or croak 'usage: $io->print(ARGS)';
397 @_ >= 2 or croak 'usage: $io->printf(FMT,[ARGS])';
403 @_ == 1 or croak 'usage: $io->getline()';
405 return scalar <$this>;
408 *gets = \&getline; # deprecated
411 @_ == 1 or croak 'usage: $io->getlines()';
413 croak 'Can\'t call $io->getlines in a scalar context, use $io->getline';
419 @_ == 2 or croak 'usage: $io->truncate(LEN)';
420 truncate($_[0], $_[1]);
424 @_ == 3 || @_ == 4 or croak 'usage: $io->read(BUF, LEN [, OFFSET])';
425 read($_[0], $_[1], $_[2], $_[3] || 0);
429 @_ == 3 || @_ == 4 or croak 'usage: $io->sysread(BUF, LEN [, OFFSET])';
430 sysread($_[0], $_[1], $_[2], $_[3] || 0);
434 @_ >= 2 && @_ <= 4 or croak 'usage: $io->write(BUF [, LEN [, OFFSET]])';
436 $_[2] = length($_[1]) unless defined $_[2];
437 print { $_[0] } substr($_[1], $_[3] || 0, $_[2]);
441 @_ >= 2 && @_ <= 4 or croak 'usage: $io->syswrite(BUF [, LEN [, OFFSET]])';
442 if (defined($_[2])) {
443 syswrite($_[0], $_[1], $_[2], $_[3] || 0);
445 syswrite($_[0], $_[1]);
450 @_ == 1 or croak 'usage: $io->stat()';
454 ################################################
455 ## State modification functions.
459 my $old = new SelectSaver qualify($_[0], caller);
461 $| = @_ > 1 ? $_[1] : 1;
465 sub output_field_separator {
466 carp "output_field_separator is not supported on a per-handle basis"
469 $, = $_[1] if @_ > 1;
473 sub output_record_separator {
474 carp "output_record_separator is not supported on a per-handle basis"
477 $\ = $_[1] if @_ > 1;
481 sub input_record_separator {
482 carp "input_record_separator is not supported on a per-handle basis"
485 $/ = $_[1] if @_ > 1;
489 sub input_line_number {
491 my $tell = tell qualify($_[0], caller) if ref($_[0]);
493 $. = $_[1] if @_ > 1;
497 sub format_page_number {
498 my $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
500 $% = $_[1] if @_ > 1;
504 sub format_lines_per_page {
505 my $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
507 $= = $_[1] if @_ > 1;
511 sub format_lines_left {
512 my $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
514 $- = $_[1] if @_ > 1;
519 my $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
521 $~ = qualify($_[1], caller) if @_ > 1;
525 sub format_top_name {
526 my $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
528 $^ = qualify($_[1], caller) if @_ > 1;
532 sub format_line_break_characters {
533 carp "format_line_break_characters is not supported on a per-handle basis"
536 $: = $_[1] if @_ > 1;
540 sub format_formfeed {
541 carp "format_formfeed is not supported on a per-handle basis"
544 $^L = $_[1] if @_ > 1;
553 formline($picture, @_);
558 @_ < 3 || croak 'usage: $io->write( [FORMAT_NAME] )';
561 my $oldfmt = $io->format_name($fmt);
563 $io->format_name($oldfmt);
571 @_ == 3 || croak 'usage: $io->fcntl( OP, VALUE );';
573 return fcntl($io, $op, $_[2]);
578 @_ == 3 || croak 'usage: $io->ioctl( OP, VALUE );';
580 return ioctl($io, $op, $_[2]);
583 # this sub is for compatability with older releases of IO that used
584 # a sub called constant to detemine if a constant existed -- GMB
586 # The SEEK_* and _IO?BF constants were the only constants at that time
587 # any new code should just chech defined(&CONSTANT_NAME)
592 (($name =~ /^(SEEK_(SET|CUR|END)|_IO[FLN]BF)$/) && defined &{$name})
593 ? &{$name}() : undef;
597 # so that flush.pl can be depriciated
601 my $old = new SelectSaver qualify($io, caller) if ref($io);