1IO::Handle(3pm) Perl Programmers Reference Guide IO::Handle(3pm)
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6 IO::Handle - supply object methods for I/O handles
7
9 use IO::Handle;
10 $io = IO::Handle->new();
12 if ($io->fdopen(fileno(STDIN),"r")) {
13 print $io->getline;
14 $io->close;
15 }
16 $io = IO::Handle->new();
18 if ($io->fdopen(fileno(STDOUT),"w")) {
19 $io->print("Some text\n");
20 }
21 # 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);
25 undef $io; # automatically closes the file if it's open
27 autoflush STDOUT 1;
29
31 "IO::Handle" is the base class for all other IO handle classes. It is
32 not intended that objects of "IO::Handle" would be created directly,
33 but instead "IO::Handle" is inherited from by several other classes in
34 the IO hierarchy.
35 If you are reading this documentation, looking for a replacement for
37 the "FileHandle" package, then I suggest you read the documentation for
38 "IO::File" too.
39
41 new ()
42 Creates a new "IO::Handle" object.
43 new_from_fd ( FD, MODE )
45 Creates an "IO::Handle" like "new" does. It requires two
46 parameters, which are passed to the method "fdopen"; if the fdopen
47 fails, the object is destroyed. Otherwise, it is returned to the
48 caller.
49
51 See perlfunc for complete descriptions of each of the following
52 supported "IO::Handle" methods, which are just front ends for the
53 corresponding built-in functions:
54 $io->close
56 $io->eof
57 $io->fcntl( FUNCTION, SCALAR )
58 $io->fileno
59 $io->format_write( [FORMAT_NAME] )
60 $io->getc
61 $io->ioctl( FUNCTION, SCALAR )
62 $io->read ( BUF, LEN, [OFFSET] )
63 $io->print ( ARGS )
64 $io->printf ( FMT, [ARGS] )
65 $io->say ( ARGS )
66 $io->stat
67 $io->sysread ( BUF, LEN, [OFFSET] )
68 $io->syswrite ( BUF, [LEN, [OFFSET]] )
69 $io->truncate ( LEN )
70 See perlvar for complete descriptions of each of the following
72 supported "IO::Handle" methods. All of them return the previous value
73 of the attribute and takes an optional single argument that when given
74 will set the value. If no argument is given the previous value is
75 unchanged (except for $io->autoflush will actually turn ON autoflush by
76 default).
77 $io->autoflush ( [BOOL] ) $|
79 $io->format_page_number( [NUM] ) $%
80 $io->format_lines_per_page( [NUM] ) $=
81 $io->format_lines_left( [NUM] ) $-
82 $io->format_name( [STR] ) $~
83 $io->format_top_name( [STR] ) $^
84 $io->input_line_number( [NUM]) $.
85 The following methods are not supported on a per-filehandle basis.
87 IO::Handle->format_line_break_characters( [STR] ) $:
89 IO::Handle->format_formfeed( [STR]) $^L
90 IO::Handle->output_field_separator( [STR] ) $,
91 IO::Handle->output_record_separator( [STR] ) $\
92 IO::Handle->input_record_separator( [STR] ) $/
94 Furthermore, for doing normal I/O you might need these:
96 $io->fdopen ( FD, MODE )
98 "fdopen" is like an ordinary "open" except that its first parameter
99 is not a filename but rather a file handle name, an IO::Handle
100 object, or a file descriptor number. (For the documentation of the
101 "open" method, see IO::File.)
102 $io->opened
104 Returns true if the object is currently a valid file descriptor,
105 false otherwise.
106 $io->getline
108 This works like <$io> described in "I/O Operators" in perlop except
109 that it's more readable and can be safely called in a list context
110 but still returns just one line. If used as the conditional
111 +within a "while" or C-style "for" loop, however, you will need to
112 +emulate the functionality of <$io> with "defined($_ =
113 $io->getline)".
114 $io->getlines
116 This works like <$io> when called in a list context to read all the
117 remaining lines in a file, except that it's more readable. It will
118 also croak() if accidentally called in a scalar context.
119 $io->ungetc ( ORD )
121 Pushes a character with the given ordinal value back onto the given
122 handle's input stream. Only one character of pushback per handle
123 is guaranteed.
124 $io->write ( BUF, LEN [, OFFSET ] )
126 This "write" is like "write" found in C, that is it is the opposite
127 of read. The wrapper for the perl "write" function is called
128 "format_write".
129 $io->error
131 Returns a true value if the given handle has experienced any errors
132 since it was opened or since the last call to "clearerr", or if the
133 handle is invalid. It only returns false for a valid handle with no
134 outstanding errors.
135 $io->clearerr
137 Clear the given handle's error indicator. Returns -1 if the handle
138 is invalid, 0 otherwise.
139 $io->sync
141 "sync" synchronizes a file's in-memory state with that on the
142 physical medium. "sync" does not operate at the perlio api level,
143 but operates on the file descriptor (similar to sysread, sysseek
144 and systell). This means that any data held at the perlio api level
145 will not be synchronized. To synchronize data that is buffered at
146 the perlio api level you must use the flush method. "sync" is not
147 implemented on all platforms. Returns "0 but true" on success,
148 "undef" on error, "undef" for an invalid handle. See fsync(3c).
149 $io->flush
151 "flush" causes perl to flush any buffered data at the perlio api
152 level. Any unread data in the buffer will be discarded, and any
153 unwritten data will be written to the underlying file descriptor.
154 Returns "0 but true" on success, "undef" on error.
155 $io->printflush ( ARGS )
157 Turns on autoflush, print ARGS and then restores the autoflush
158 status of the "IO::Handle" object. Returns the return value from
159 print.
160 $io->blocking ( [ BOOL ] )
162 If called with an argument "blocking" will turn on non-blocking IO
163 if "BOOL" is false, and turn it off if "BOOL" is true.
164 "blocking" will return the value of the previous setting, or the
166 current setting if "BOOL" is not given.
167 If an error occurs "blocking" will return undef and $! will be set.
169 If the C functions setbuf() and/or setvbuf() are available, then
171 "IO::Handle::setbuf" and "IO::Handle::setvbuf" set the buffering policy
172 for an IO::Handle. The calling sequences for the Perl functions are
173 the same as their C counterparts--including the constants "_IOFBF",
174 "_IOLBF", and "_IONBF" for setvbuf()--except that the buffer parameter
175 specifies a scalar variable to use as a buffer. You should only change
176 the buffer before any I/O, or immediately after calling flush.
177 WARNING: The IO::Handle::setvbuf() is not available by default on Perls
179 5.8.0 and later because setvbuf() is rather specific to using the stdio
180 library, while Perl prefers the new perlio subsystem instead.
181 WARNING: A variable used as a buffer by "setbuf" or "setvbuf" must not
183 be modified in any way until the IO::Handle is closed or "setbuf" or
184 "setvbuf" is called again, or memory corruption may result! Remember
185 that the order of global destruction is undefined, so even if your
186 buffer variable remains in scope until program termination, it may be
187 undefined before the file IO::Handle is closed. Note that you need to
188 import the constants "_IOFBF", "_IOLBF", and "_IONBF" explicitly. Like
189 C, setbuf returns nothing. setvbuf returns "0 but true", on success,
190 "undef" on failure.
191 Lastly, there is a special method for working under -T and setuid/gid
193 scripts:
194 $io->untaint
196 Marks the object as taint-clean, and as such data read from it will
197 also be considered taint-clean. Note that this is a very trusting
198 action to take, and appropriate consideration for the data source
199 and potential vulnerability should be kept in mind. Returns 0 on
200 success, -1 if setting the taint-clean flag failed. (eg invalid
201 handle)
202
204 An "IO::Handle" object is a reference to a symbol/GLOB reference (see
205 the "Symbol" package). Some modules that inherit from "IO::Handle" may
206 want to keep object related variables in the hash table part of the
207 GLOB. In an attempt to prevent modules trampling on each other I
208 propose the that any such module should prefix its variables with its
209 own name separated by _'s. For example the IO::Socket module keeps a
210 "timeout" variable in 'io_socket_timeout'.
211
213 perlfunc, "I/O Operators" in perlop, IO::File
214
216 Due to backwards compatibility, all filehandles resemble objects of
217 class "IO::Handle", or actually classes derived from that class. They
218 actually aren't. Which means you can't derive your own class from
219 "IO::Handle" and inherit those methods.
220
222 Derived from FileHandle.pm by Graham Barr <gbarr@pobox.com>
223perl v5.16.3 2013-03-04 IO::Handle(3pm)