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| 129 | .\" ======================================================================== |
| 130 | .\" |
| 131 | .IX Title "IO::Handle 3" |
| 132 | .TH IO::Handle 3 "2002-06-01" "perl v5.8.0" "Perl Programmers Reference Guide" |
| 133 | .SH "NAME" |
| 134 | IO::Handle \- supply object methods for I/O handles |
| 135 | .SH "SYNOPSIS" |
| 136 | .IX Header "SYNOPSIS" |
| 137 | .Vb 1 |
| 138 | \& use IO::Handle; |
| 139 | .Ve |
| 140 | .PP |
| 141 | .Vb 5 |
| 142 | \& $io = new IO::Handle; |
| 143 | \& if ($io->fdopen(fileno(STDIN),"r")) { |
| 144 | \& print $io->getline; |
| 145 | \& $io->close; |
| 146 | \& } |
| 147 | .Ve |
| 148 | .PP |
| 149 | .Vb 4 |
| 150 | \& $io = new IO::Handle; |
| 151 | \& if ($io->fdopen(fileno(STDOUT),"w")) { |
| 152 | \& $io->print("Some text\en"); |
| 153 | \& } |
| 154 | .Ve |
| 155 | .PP |
| 156 | .Vb 2 |
| 157 | \& use IO::Handle '_IOLBF'; |
| 158 | \& $io->setvbuf($buffer_var, _IOLBF, 1024); |
| 159 | .Ve |
| 160 | .PP |
| 161 | .Vb 1 |
| 162 | \& undef $io; # automatically closes the file if it's open |
| 163 | .Ve |
| 164 | .PP |
| 165 | .Vb 1 |
| 166 | \& autoflush STDOUT 1; |
| 167 | .Ve |
| 168 | .SH "DESCRIPTION" |
| 169 | .IX Header "DESCRIPTION" |
| 170 | \&\f(CW\*(C`IO::Handle\*(C'\fR is the base class for all other \s-1IO\s0 handle classes. It is |
| 171 | not intended that objects of \f(CW\*(C`IO::Handle\*(C'\fR would be created directly, |
| 172 | but instead \f(CW\*(C`IO::Handle\*(C'\fR is inherited from by several other classes |
| 173 | in the \s-1IO\s0 hierarchy. |
| 174 | .PP |
| 175 | If you are reading this documentation, looking for a replacement for |
| 176 | the \f(CW\*(C`FileHandle\*(C'\fR package, then I suggest you read the documentation |
| 177 | for \f(CW\*(C`IO::File\*(C'\fR too. |
| 178 | .SH "CONSTRUCTOR" |
| 179 | .IX Header "CONSTRUCTOR" |
| 180 | .IP "new ()" 4 |
| 181 | .IX Item "new ()" |
| 182 | Creates a new \f(CW\*(C`IO::Handle\*(C'\fR object. |
| 183 | .IP "new_from_fd ( \s-1FD\s0, \s-1MODE\s0 )" 4 |
| 184 | .IX Item "new_from_fd ( FD, MODE )" |
| 185 | Creates an \f(CW\*(C`IO::Handle\*(C'\fR like \f(CW\*(C`new\*(C'\fR does. |
| 186 | It requires two parameters, which are passed to the method \f(CW\*(C`fdopen\*(C'\fR; |
| 187 | if the fdopen fails, the object is destroyed. Otherwise, it is returned |
| 188 | to the caller. |
| 189 | .SH "METHODS" |
| 190 | .IX Header "METHODS" |
| 191 | See perlfunc for complete descriptions of each of the following |
| 192 | supported \f(CW\*(C`IO::Handle\*(C'\fR methods, which are just front ends for the |
| 193 | corresponding built-in functions: |
| 194 | .PP |
| 195 | .Vb 12 |
| 196 | \& $io->close |
| 197 | \& $io->eof |
| 198 | \& $io->fileno |
| 199 | \& $io->format_write( [FORMAT_NAME] ) |
| 200 | \& $io->getc |
| 201 | \& $io->read ( BUF, LEN, [OFFSET] ) |
| 202 | \& $io->print ( ARGS ) |
| 203 | \& $io->printf ( FMT, [ARGS] ) |
| 204 | \& $io->stat |
| 205 | \& $io->sysread ( BUF, LEN, [OFFSET] ) |
| 206 | \& $io->syswrite ( BUF, [LEN, [OFFSET]] ) |
| 207 | \& $io->truncate ( LEN ) |
| 208 | .Ve |
| 209 | .PP |
| 210 | See perlvar for complete descriptions of each of the following |
| 211 | supported \f(CW\*(C`IO::Handle\*(C'\fR methods. All of them return the previous |
| 212 | value of the attribute and takes an optional single argument that when |
| 213 | given will set the value. If no argument is given the previous value |
| 214 | is unchanged (except for \f(CW$io\fR\->autoflush will actually turn \s-1ON\s0 |
| 215 | autoflush by default). |
| 216 | .PP |
| 217 | .Vb 7 |
| 218 | \& $io->autoflush ( [BOOL] ) $| |
| 219 | \& $io->format_page_number( [NUM] ) $% |
| 220 | \& $io->format_lines_per_page( [NUM] ) $= |
| 221 | \& $io->format_lines_left( [NUM] ) $- |
| 222 | \& $io->format_name( [STR] ) $~ |
| 223 | \& $io->format_top_name( [STR] ) $^ |
| 224 | \& $io->input_line_number( [NUM]) $. |
| 225 | .Ve |
| 226 | .PP |
| 227 | The following methods are not supported on a per-filehandle basis. |
| 228 | .PP |
| 229 | .Vb 4 |
| 230 | \& IO::Handle->format_line_break_characters( [STR] ) $: |
| 231 | \& IO::Handle->format_formfeed( [STR]) $^L |
| 232 | \& IO::Handle->output_field_separator( [STR] ) $, |
| 233 | \& IO::Handle->output_record_separator( [STR] ) $\e |
| 234 | .Ve |
| 235 | .PP |
| 236 | .Vb 1 |
| 237 | \& IO::Handle->input_record_separator( [STR] ) $/ |
| 238 | .Ve |
| 239 | .PP |
| 240 | Furthermore, for doing normal I/O you might need these: |
| 241 | .IP "$io\->fdopen ( \s-1FD\s0, \s-1MODE\s0 )" 4 |
| 242 | .IX Item "$io->fdopen ( FD, MODE )" |
| 243 | \&\f(CW\*(C`fdopen\*(C'\fR is like an ordinary \f(CW\*(C`open\*(C'\fR except that its first parameter |
| 244 | is not a filename but rather a file handle name, an IO::Handle object, |
| 245 | or a file descriptor number. |
| 246 | .IP "$io\->opened" 4 |
| 247 | .IX Item "$io->opened" |
| 248 | Returns true if the object is currently a valid file descriptor, false |
| 249 | otherwise. |
| 250 | .IP "$io\->getline" 4 |
| 251 | .IX Item "$io->getline" |
| 252 | This works like <$io> described in \*(L"I/O Operators\*(R" in perlop |
| 253 | except that it's more readable and can be safely called in a |
| 254 | list context but still returns just one line. |
| 255 | .IP "$io\->getlines" 4 |
| 256 | .IX Item "$io->getlines" |
| 257 | This works like <$io> when called in a list context to read all |
| 258 | the remaining lines in a file, except that it's more readable. |
| 259 | It will also \fIcroak()\fR if accidentally called in a scalar context. |
| 260 | .IP "$io\->ungetc ( \s-1ORD\s0 )" 4 |
| 261 | .IX Item "$io->ungetc ( ORD )" |
| 262 | Pushes a character with the given ordinal value back onto the given |
| 263 | handle's input stream. Only one character of pushback per handle is |
| 264 | guaranteed. |
| 265 | .IP "$io\->write ( \s-1BUF\s0, \s-1LEN\s0 [, \s-1OFFSET\s0 ] )" 4 |
| 266 | .IX Item "$io->write ( BUF, LEN [, OFFSET ] )" |
| 267 | This \f(CW\*(C`write\*(C'\fR is like \f(CW\*(C`write\*(C'\fR found in C, that is it is the |
| 268 | opposite of read. The wrapper for the perl \f(CW\*(C`write\*(C'\fR function is |
| 269 | called \f(CW\*(C`format_write\*(C'\fR. |
| 270 | .IP "$io\->error" 4 |
| 271 | .IX Item "$io->error" |
| 272 | Returns a true value if the given handle has experienced any errors |
| 273 | since it was opened or since the last call to \f(CW\*(C`clearerr\*(C'\fR, or if the |
| 274 | handle is invalid. It only returns false for a valid handle with no |
| 275 | outstanding errors. |
| 276 | .IP "$io\->clearerr" 4 |
| 277 | .IX Item "$io->clearerr" |
| 278 | Clear the given handle's error indicator. Returns \-1 if the handle is |
| 279 | invalid, 0 otherwise. |
| 280 | .IP "$io\->sync" 4 |
| 281 | .IX Item "$io->sync" |
| 282 | \&\f(CW\*(C`sync\*(C'\fR synchronizes a file's in-memory state with that on the |
| 283 | physical medium. \f(CW\*(C`sync\*(C'\fR does not operate at the perlio api level, but |
| 284 | operates on the file descriptor (similar to sysread, sysseek and |
| 285 | systell). This means that any data held at the perlio api level will not |
| 286 | be synchronized. To synchronize data that is buffered at the perlio api |
| 287 | level you must use the flush method. \f(CW\*(C`sync\*(C'\fR is not implemented on all |
| 288 | platforms. Returns \*(L"0 but true\*(R" on success, \f(CW\*(C`undef\*(C'\fR on error, \f(CW\*(C`undef\*(C'\fR |
| 289 | for an invalid handle. See \fIfsync\fR\|(3c). |
| 290 | .IP "$io\->flush" 4 |
| 291 | .IX Item "$io->flush" |
| 292 | \&\f(CW\*(C`flush\*(C'\fR causes perl to flush any buffered data at the perlio api level. |
| 293 | Any unread data in the buffer will be discarded, and any unwritten data |
| 294 | will be written to the underlying file descriptor. Returns \*(L"0 but true\*(R" |
| 295 | on success, \f(CW\*(C`undef\*(C'\fR on error. |
| 296 | .IP "$io\->printflush ( \s-1ARGS\s0 )" 4 |
| 297 | .IX Item "$io->printflush ( ARGS )" |
| 298 | Turns on autoflush, print \s-1ARGS\s0 and then restores the autoflush status of the |
| 299 | \&\f(CW\*(C`IO::Handle\*(C'\fR object. Returns the return value from print. |
| 300 | .IP "$io\->blocking ( [ \s-1BOOL\s0 ] )" 4 |
| 301 | .IX Item "$io->blocking ( [ BOOL ] )" |
| 302 | If called with an argument \f(CW\*(C`blocking\*(C'\fR will turn on non-blocking \s-1IO\s0 if |
| 303 | \&\f(CW\*(C`BOOL\*(C'\fR is false, and turn it off if \f(CW\*(C`BOOL\*(C'\fR is true. |
| 304 | .Sp |
| 305 | \&\f(CW\*(C`blocking\*(C'\fR will return the value of the previous setting, or the |
| 306 | current setting if \f(CW\*(C`BOOL\*(C'\fR is not given. |
| 307 | .Sp |
| 308 | If an error occurs \f(CW\*(C`blocking\*(C'\fR will return undef and \f(CW$!\fR will be set. |
| 309 | .PP |
| 310 | If the C functions \fIsetbuf()\fR and/or \fIsetvbuf()\fR are available, then |
| 311 | \&\f(CW\*(C`IO::Handle::setbuf\*(C'\fR and \f(CW\*(C`IO::Handle::setvbuf\*(C'\fR set the buffering |
| 312 | policy for an IO::Handle. The calling sequences for the Perl functions |
| 313 | are the same as their C counterparts\*(--including the constants \f(CW\*(C`_IOFBF\*(C'\fR, |
| 314 | \&\f(CW\*(C`_IOLBF\*(C'\fR, and \f(CW\*(C`_IONBF\*(C'\fR for \fIsetvbuf()\fR\-\-except that the buffer parameter |
| 315 | specifies a scalar variable to use as a buffer. You should only |
| 316 | change the buffer before any I/O, or immediately after calling flush. |
| 317 | .PP |
| 318 | \&\s-1WARNING:\s0 A variable used as a buffer by \f(CW\*(C`setbuf\*(C'\fR or \f(CW\*(C`setvbuf\*(C'\fR \fBmust not |
| 319 | be modified\fR in any way until the IO::Handle is closed or \f(CW\*(C`setbuf\*(C'\fR or |
| 320 | \&\f(CW\*(C`setvbuf\*(C'\fR is called again, or memory corruption may result! Remember that |
| 321 | the order of global destruction is undefined, so even if your buffer |
| 322 | variable remains in scope until program termination, it may be undefined |
| 323 | before the file IO::Handle is closed. Note that you need to import the |
| 324 | constants \f(CW\*(C`_IOFBF\*(C'\fR, \f(CW\*(C`_IOLBF\*(C'\fR, and \f(CW\*(C`_IONBF\*(C'\fR explicitly. Like C, setbuf |
| 325 | returns nothing. setvbuf returns \*(L"0 but true\*(R", on success, \f(CW\*(C`undef\*(C'\fR on |
| 326 | failure. |
| 327 | .PP |
| 328 | Lastly, there is a special method for working under \fB\-T\fR and setuid/gid |
| 329 | scripts: |
| 330 | .IP "$io\->untaint" 4 |
| 331 | .IX Item "$io->untaint" |
| 332 | Marks the object as taint\-clean, and as such data read from it will also |
| 333 | be considered taint\-clean. Note that this is a very trusting action to |
| 334 | take, and appropriate consideration for the data source and potential |
| 335 | vulnerability should be kept in mind. Returns 0 on success, \-1 if setting |
| 336 | the taint-clean flag failed. (eg invalid handle) |
| 337 | .SH "NOTE" |
| 338 | .IX Header "NOTE" |
| 339 | An \f(CW\*(C`IO::Handle\*(C'\fR object is a reference to a symbol/GLOB reference (see |
| 340 | the \f(CW\*(C`Symbol\*(C'\fR package). Some modules that |
| 341 | inherit from \f(CW\*(C`IO::Handle\*(C'\fR may want to keep object related variables |
| 342 | in the hash table part of the \s-1GLOB\s0. In an attempt to prevent modules |
| 343 | trampling on each other I propose the that any such module should prefix |
| 344 | its variables with its own name separated by _'s. For example the IO::Socket |
| 345 | module keeps a \f(CW\*(C`timeout\*(C'\fR variable in 'io_socket_timeout'. |
| 346 | .SH "SEE ALSO" |
| 347 | .IX Header "SEE ALSO" |
| 348 | perlfunc, |
| 349 | \&\*(L"I/O Operators\*(R" in perlop, |
| 350 | IO::File |
| 351 | .SH "BUGS" |
| 352 | .IX Header "BUGS" |
| 353 | Due to backwards compatibility, all filehandles resemble objects |
| 354 | of class \f(CW\*(C`IO::Handle\*(C'\fR, or actually classes derived from that class. |
| 355 | They actually aren't. Which means you can't derive your own |
| 356 | class from \f(CW\*(C`IO::Handle\*(C'\fR and inherit those methods. |
| 357 | .SH "HISTORY" |
| 358 | .IX Header "HISTORY" |
| 359 | Derived from FileHandle.pm by Graham Barr <\fIgbarr@pobox.com\fR> |