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 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: 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 but true", on success, C<undef> on
206 Lastly, there is a special method for working under B<-T> and setuid/gid
213 Marks the object as taint-clean, and as such data read from it will also
214 be considered taint-clean. Note that this is a very trusting action to
215 take, and appropriate consideration for the data source and potential
216 vulnerability should be kept in mind. Returns 0 on success, -1 if setting
217 the taint-clean flag failed. (eg invalid handle)
223 A C<IO::Handle> object is a reference to a symbol/GLOB reference (see
224 the C<Symbol> package). Some modules that
225 inherit from C<IO::Handle> may want to keep object related variables
226 in the hash table part of the GLOB. In an attempt to prevent modules
227 trampling on each other I propose the that any such module should prefix
228 its variables with its own name separated by _'s. For example the IO::Socket
229 module keeps a C<timeout> variable in 'io_socket_timeout'.
234 L<perlop/"I/O Operators">,
239 Due to backwards compatibility, all filehandles resemble objects
240 of class C<IO::Handle>, or actually classes derived from that class.
241 They actually aren't. Which means you can't derive your own
242 class from C<IO::Handle> and inherit those methods.
246 Derived from FileHandle.pm by Graham Barr E<lt>F<gbarr@pobox.com>E<gt>
252 our($VERSION, @EXPORT_OK, @ISA);
256 use IO (); # Load the XS module
261 $VERSION = "1.21_00";
265 output_field_separator
266 output_record_separator
267 input_record_separator
270 format_lines_per_page
274 format_line_break_characters
294 ################################################
295 ## Constructors, destructors.
299 my $class = ref($_[0]) || $_[0] || "IO::Handle";
300 @_ == 1 or croak "usage: new $class";
306 my $class = ref($_[0]) || $_[0] || "IO::Handle";
307 @_ == 3 or croak "usage: new_from_fd $class FD, MODE";
310 IO::Handle::fdopen($io, @_)
316 # There is no need for DESTROY to do anything, because when the
317 # last reference to an IO object is gone, Perl automatically
318 # closes its associated files (if any). However, to avoid any
319 # attempts to autoload DESTROY, we here define it to do nothing.
324 ################################################
328 sub _open_mode_string {
330 $mode =~ /^\+?(<|>>?)$/
331 or $mode =~ s/^r(\+?)$/$1</
332 or $mode =~ s/^w(\+?)$/$1>/
333 or $mode =~ s/^a(\+?)$/$1>>/
334 or croak "IO::Handle: bad open mode: $mode";
339 @_ == 3 or croak 'usage: $io->fdopen(FD, MODE)';
340 my ($io, $fd, $mode) = @_;
343 if (ref($fd) && "".$fd =~ /GLOB\(/o) {
344 # It's a glob reference; Alias it as we cannot get name of anon GLOBs
345 my $n = qualify(*GLOB);
348 } elsif ($fd =~ m#^\d+$#) {
349 # It's an FD number; prefix with "=".
353 open($io, _open_mode_string($mode) . '&' . $fd)
358 @_ == 1 or croak 'usage: $io->close()';
364 ################################################
365 ## Normal I/O functions.
372 @_ == 1 or croak 'usage: $io->opened()';
373 defined fileno($_[0]);
377 @_ == 1 or croak 'usage: $io->fileno()';
382 @_ == 1 or croak 'usage: $io->getc()';
387 @_ == 1 or croak 'usage: $io->eof()';
392 @_ or croak 'usage: $io->print(ARGS)';
398 @_ >= 2 or croak 'usage: $io->printf(FMT,[ARGS])';
404 @_ == 1 or croak 'usage: $io->getline()';
406 return scalar <$this>;
409 *gets = \&getline; # deprecated
412 @_ == 1 or croak 'usage: $io->getlines()';
414 croak 'Can\'t call $io->getlines in a scalar context, use $io->getline';
420 @_ == 2 or croak 'usage: $io->truncate(LEN)';
421 truncate($_[0], $_[1]);
425 @_ == 3 || @_ == 4 or croak 'usage: $io->read(BUF, LEN [, OFFSET])';
426 read($_[0], $_[1], $_[2], $_[3] || 0);
430 @_ == 3 || @_ == 4 or croak 'usage: $io->sysread(BUF, LEN [, OFFSET])';
431 sysread($_[0], $_[1], $_[2], $_[3] || 0);
435 @_ >= 2 && @_ <= 4 or croak 'usage: $io->write(BUF [, LEN [, OFFSET]])';
437 $_[2] = length($_[1]) unless defined $_[2];
438 print { $_[0] } substr($_[1], $_[3] || 0, $_[2]);
442 @_ >= 2 && @_ <= 4 or croak 'usage: $io->syswrite(BUF [, LEN [, OFFSET]])';
443 if (defined($_[2])) {
444 syswrite($_[0], $_[1], $_[2], $_[3] || 0);
446 syswrite($_[0], $_[1]);
451 @_ == 1 or croak 'usage: $io->stat()';
455 ################################################
456 ## State modification functions.
460 my $old = new SelectSaver qualify($_[0], caller);
462 $| = @_ > 1 ? $_[1] : 1;
466 sub output_field_separator {
467 carp "output_field_separator is not supported on a per-handle basis"
470 $, = $_[1] if @_ > 1;
474 sub output_record_separator {
475 carp "output_record_separator is not supported on a per-handle basis"
478 $\ = $_[1] if @_ > 1;
482 sub input_record_separator {
483 carp "input_record_separator is not supported on a per-handle basis"
486 $/ = $_[1] if @_ > 1;
490 sub input_line_number {
492 my $tell = tell qualify($_[0], caller) if ref($_[0]);
494 $. = $_[1] if @_ > 1;
498 sub format_page_number {
499 my $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
501 $% = $_[1] if @_ > 1;
505 sub format_lines_per_page {
506 my $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
508 $= = $_[1] if @_ > 1;
512 sub format_lines_left {
513 my $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
515 $- = $_[1] if @_ > 1;
520 my $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
522 $~ = qualify($_[1], caller) if @_ > 1;
526 sub format_top_name {
527 my $old = new SelectSaver qualify($_[0], caller) if ref($_[0]);
529 $^ = qualify($_[1], caller) if @_ > 1;
533 sub format_line_break_characters {
534 carp "format_line_break_characters is not supported on a per-handle basis"
537 $: = $_[1] if @_ > 1;
541 sub format_formfeed {
542 carp "format_formfeed is not supported on a per-handle basis"
545 $^L = $_[1] if @_ > 1;
554 formline($picture, @_);
559 @_ < 3 || croak 'usage: $io->write( [FORMAT_NAME] )';
562 my $oldfmt = $io->format_name($fmt);
564 $io->format_name($oldfmt);
572 @_ == 3 || croak 'usage: $io->fcntl( OP, VALUE );';
574 return fcntl($io, $op, $_[2]);
579 @_ == 3 || croak 'usage: $io->ioctl( OP, VALUE );';
581 return ioctl($io, $op, $_[2]);
584 # this sub is for compatability with older releases of IO that used
585 # a sub called constant to detemine if a constant existed -- GMB
587 # The SEEK_* and _IO?BF constants were the only constants at that time
588 # any new code should just chech defined(&CONSTANT_NAME)
593 (($name =~ /^(SEEK_(SET|CUR|END)|_IO[FLN]BF)$/) && defined &{$name})
594 ? &{$name}() : undef;
598 # so that flush.pl can be depriciated
602 my $old = new SelectSaver qualify($io, caller) if ref($io);