1IO::Handle(3pm) Perl Programmers Reference Guide IO::Handle(3pm)
2
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 within
111 a "while" or C-style "for" loop, however, you will need to emulate
112 the functionality of <$io> with "defined($_ = $io->getline)".
113 $io->getlines
115 This works like <$io> when called in a list context to read all the
116 remaining lines in a file, except that it's more readable. It will
117 also croak() if accidentally called in a scalar context.
118 $io->ungetc ( ORD )
120 Pushes a character with the given ordinal value back onto the given
121 handle's input stream. Only one character of pushback per handle
122 is guaranteed.
123 $io->write ( BUF, LEN [, OFFSET ] )
125 This "write" is somewhat like "write" found in C, in that it is the
126 opposite of read. The wrapper for the perl "write" function is
127 called "format_write". However, whilst the C "write" function
128 returns the number of bytes written, this "write" function simply
129 returns true if successful (like "print"). A more C-like "write" is
130 "syswrite" (see above).
131 $io->error
133 Returns a true value if the given handle has experienced any errors
134 since it was opened or since the last call to "clearerr", or if the
135 handle is invalid. It only returns false for a valid handle with no
136 outstanding errors.
137 $io->clearerr
139 Clear the given handle's error indicator. Returns -1 if the handle
140 is invalid, 0 otherwise.
141 $io->sync
143 "sync" synchronizes a file's in-memory state with that on the
144 physical medium. "sync" does not operate at the perlio api level,
145 but operates on the file descriptor (similar to sysread, sysseek
146 and systell). This means that any data held at the perlio api level
147 will not be synchronized. To synchronize data that is buffered at
148 the perlio api level you must use the flush method. "sync" is not
149 implemented on all platforms. Returns "0 but true" on success,
150 "undef" on error, "undef" for an invalid handle. See fsync(3c).
151 $io->flush
153 "flush" causes perl to flush any buffered data at the perlio api
154 level. Any unread data in the buffer will be discarded, and any
155 unwritten data will be written to the underlying file descriptor.
156 Returns "0 but true" on success, "undef" on error.
157 $io->printflush ( ARGS )
159 Turns on autoflush, print ARGS and then restores the autoflush
160 status of the "IO::Handle" object. Returns the return value from
161 print.
162 $io->blocking ( [ BOOL ] )
164 If called with an argument "blocking" will turn on non-blocking IO
165 if "BOOL" is false, and turn it off if "BOOL" is true.
166 "blocking" will return the value of the previous setting, or the
168 current setting if "BOOL" is not given.
169 If an error occurs "blocking" will return undef and $! will be set.
171 If the C functions setbuf() and/or setvbuf() are available, then
173 "IO::Handle::setbuf" and "IO::Handle::setvbuf" set the buffering policy
174 for an IO::Handle. The calling sequences for the Perl functions are
175 the same as their C counterparts--including the constants "_IOFBF",
176 "_IOLBF", and "_IONBF" for setvbuf()--except that the buffer parameter
177 specifies a scalar variable to use as a buffer. You should only change
178 the buffer before any I/O, or immediately after calling flush.
179 WARNING: The IO::Handle::setvbuf() is not available by default on Perls
181 5.8.0 and later because setvbuf() is rather specific to using the stdio
182 library, while Perl prefers the new perlio subsystem instead.
183 WARNING: A variable used as a buffer by "setbuf" or "setvbuf" must not
185 be modified in any way until the IO::Handle is closed or "setbuf" or
186 "setvbuf" is called again, or memory corruption may result! Remember
187 that the order of global destruction is undefined, so even if your
188 buffer variable remains in scope until program termination, it may be
189 undefined before the file IO::Handle is closed. Note that you need to
190 import the constants "_IOFBF", "_IOLBF", and "_IONBF" explicitly. Like
191 C, setbuf returns nothing. setvbuf returns "0 but true", on success,
192 "undef" on failure.
193 Lastly, there is a special method for working under -T and setuid/gid
195 scripts:
196 $io->untaint
198 Marks the object as taint-clean, and as such data read from it will
199 also be considered taint-clean. Note that this is a very trusting
200 action to take, and appropriate consideration for the data source
201 and potential vulnerability should be kept in mind. Returns 0 on
202 success, -1 if setting the taint-clean flag failed. (eg invalid
203 handle)
204
206 An "IO::Handle" object is a reference to a symbol/GLOB reference (see
207 the "Symbol" package). Some modules that inherit from "IO::Handle" may
208 want to keep object related variables in the hash table part of the
209 GLOB. In an attempt to prevent modules trampling on each other I
210 propose the that any such module should prefix its variables with its
211 own name separated by _'s. For example the IO::Socket module keeps a
212 "timeout" variable in 'io_socket_timeout'.
213
215 perlfunc, "I/O Operators" in perlop, IO::File
216
218 Due to backwards compatibility, all filehandles resemble objects of
219 class "IO::Handle", or actually classes derived from that class. They
220 actually aren't. Which means you can't derive your own class from
221 "IO::Handle" and inherit those methods.
222
224 Derived from FileHandle.pm by Graham Barr <gbarr@pobox.com>
225perl v5.26.3 2018-03-01 IO::Handle(3pm)