raw/mann/open.n

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   8 '\" RCS: @(#) $Id: open.n,v 1.1 2003/12/20 03:31:54 bbbush Exp $
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  10 '\" The definitions below are for supplemental macros used in Tcl/Tk
  11 '\" manual entries.
  12 '\"
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  62 '\" .OP cmdName dbName dbClass
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  64 '\"     option's name as specified in the class command, dbName gives
  65 '\"     the option's name in the option database, and dbClass gives
  66 '\"     the option's class in the option database.
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  68 '\" .UL arg1 arg2
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  70 '\"
  71 '\" RCS: @(#) $Id: open.n,v 1.1 2003/12/20 03:31:54 bbbush Exp $
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  73 '\"     # Set up traps and other miscellaneous stuff for Tcl/Tk man pages.
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 177 .el \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c
 178 .\}
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 182 .\}
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 207 .de SO
 208 .SH "STANDARD OPTIONS"
 209 .LP
 210 .nf
 211 .ta 5.5c 11c
 212 .ft B
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 215 .de SE
 216 .fi
 217 .ft R
 218 .LP
 219 See the \\fBoptions\\fR manual entry for details on the standard options.
 220 ..
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 222 .de OP
 223 .LP
 224 .nf
 225 .ta 4c
 226 Command-Line Name:      \\fB\\$1\\fR
 227 Database Name:  \\fB\\$2\\fR
 228 Database Class: \\fB\\$3\\fR
 229 .fi
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 243 .de UL
 244 \\$1\l'|0\(ul'\\$2
 245 ..
 246 .TH open n 7.6 Tcl "Tcl Built-In Commands"
 247 .BS
 248 '\" Note:  do not modify the .SH NAME line immediately below!
 249 .SH NAME
 250 open \- Open a file-based or command pipeline channel
 251 .SH SYNOPSIS
 252 .sp
 253 \fBopen \fIfileName\fR
 254 .br
 255 \fBopen \fIfileName access\fR
 256 .br
 257 \fBopen \fIfileName access permissions\fR
 258 .BE
 259
 260 .SH DESCRIPTION
 261 .PP
 262 .VS
 263 This command opens a file, serial port, or command pipeline and returns a
 264 .VE
 265 channel identifier that may be used in future invocations of commands like
 266 \fBread\fR, \fBputs\fR, and \fBclose\fR.
 267 If the first character of \fIfileName\fR is not \fB|\fR then
 268 the command opens a file:
 269 \fIfileName\fR gives the name of the file to open, and it must conform to the
 270 conventions described in the \fBfilename\fR manual entry.
 271 .PP
 272 The \fIaccess\fR argument, if present, indicates the way in which the file
 273 (or command pipeline) is to be accessed.
 274 In the first form \fIaccess\fR may have any of the following values:
 275 .TP 15
 276 \fBr\fR
 277 Open the file for reading only; the file must already exist. This is the
 278 default value if \fIaccess\fR is not specified.
 279 .TP 15
 280 \fBr+\fR
 281 Open the file for both reading and writing; the file must
 282 already exist.
 283 .TP 15
 284 \fBw\fR
 285 Open the file for writing only.  Truncate it if it exists.  If it doesn't
 286 exist, create a new file.
 287 .TP 15
 288 \fBw+\fR
 289 Open the file for reading and writing.  Truncate it if it exists.
 290 If it doesn't exist, create a new file.
 291 .TP 15
 292 \fBa\fR
 293 Open the file for writing only.  If the file doesn't exist,
 294 create a new empty file.
 295 Set the initial access position  to the end of the file.
 296 .TP 15
 297 \fBa+\fR
 298 Open the file for reading and writing.  If the file doesn't exist,
 299 create a new empty file.
 300 Set the initial access position  to the end of the file.
 301 .PP
 302 In the second form, \fIaccess\fR consists of a list of any of the
 303 following flags, all of which have the standard POSIX meanings.
 304 One of the flags must be either \fBRDONLY\fR, \fBWRONLY\fR or \fBRDWR\fR.
 305 .TP 15
 306 \fBRDONLY\fR
 307 Open the file for reading only.
 308 .TP 15
 309 \fBWRONLY\fR
 310 Open the file for writing only.
 311 .TP 15
 312 \fBRDWR\fR
 313 Open the file for both reading and writing.
 314 .TP 15
 315 \fBAPPEND\fR
 316 Set the file pointer to the end of the file prior to each write.
 317 .TP 15
 318 \fBCREAT\fR
 319 Create the file if it doesn't already exist (without this flag it
 320 is an error for the file not to exist).
 321 .TP 15
 322 \fBEXCL\fR
 323 If \fBCREAT\fR is also specified, an error is returned if the
 324 file already exists.
 325 .TP 15
 326 \fBNOCTTY\fR
 327 If the file is a terminal device, this flag prevents the file from
 328 becoming the controlling terminal of the process.
 329 .TP 15
 330 \fBNONBLOCK\fR
 331 Prevents the process from blocking while opening the file, and
 332 possibly in subsequent I/O operations.  The exact behavior of
 333 this flag is system- and device-dependent;  its use is discouraged
 334 (it is better to use the \fBfconfigure\fR command to put a file
 335 in nonblocking mode).
 336 For details refer to your system documentation on the \fBopen\fR system
 337 call's \fBO_NONBLOCK\fR flag.
 338 .TP 15
 339 \fBTRUNC\fR
 340 If the file exists it is truncated to zero length.
 341 .PP
 342 If a new file is created as part of opening it, \fIpermissions\fR
 343 (an integer) is used to set the permissions for the new file in
 344 conjunction with the process's file mode creation mask.
 345 \fIPermissions\fR defaults to 0666.
 346 .PP
 347 '\" Not versioned as advice applies to all recent versions of Tcl.
 348 '\" Prior to that, Tcl didn't really support binary files anyway...
 349 .VS
 350 Note that if you are going to be reading or writing binary data from
 351 the channel created by this command, you should use the
 352 \fBfconfigure\fR command to change the \fB-translation\fR option of
 353 the channel to \fBbinary\fR before transferring any binary data.  This
 354 is in contrast to the ``b'' character passed as part of the equivalent
 355 of the \fIaccess\fR parameter to some versions of the C library
 356 \fIfopen()\fR function.
 357 .VE
 358 .SH "COMMAND PIPELINES"
 359 .PP
 360 If the first character of \fIfileName\fR is ``|'' then the
 361 remaining characters of \fIfileName\fR are treated as a list of arguments
 362 that describe a command pipeline to invoke, in the same style as the
 363 arguments for \fBexec\fR.
 364 In this case, the channel identifier returned by \fBopen\fR may be used
 365 to write to the command's input pipe or read from its output pipe,
 366 depending on the value of \fIaccess\fR.
 367 If write-only access is used (e.g. \fIaccess\fR is \fBw\fR), then
 368 standard output for the pipeline is directed to the current standard
 369 output unless overridden by the command.
 370 If read-only access is used (e.g. \fIaccess\fR is \fBr\fR),
 371 standard input for the pipeline is taken from the current standard
 372 input unless overridden by the command.
 373 .SH "SERIAL COMMUNICATIONS"
 374 .VS
 375 .PP
 376 If \fIfileName\fR refers to a serial port, then the specified serial port
 377 is opened and initialized in a platform-dependent manner.  Acceptable
 378 values for the \fIfileName\fR to use to open a serial port are described in
 379 the PORTABILITY ISSUES section.
 380
 381 .SH "CONFIGURATION OPTIONS"
 382 The \fBfconfigure\fR command can be used to query and set the following
 383 configuration option for open serial ports:
 384 .TP
 385 \fB\-mode \fIbaud\fB,\fIparity\fB,\fIdata\fB,\fIstop\fR
 386 .
 387 This option is a set of 4 comma-separated values: the baud rate, parity,
 388 number of data bits, and number of stop bits for this serial port.  The
 389 \fIbaud\fR rate is a simple integer that specifies the connection speed.
 390 \fIParity\fR is one of the following letters: \fBn\fR, \fBo\fR, \fBe\fR,
 391 \fBm\fR, \fBs\fR; respectively signifying the parity options of ``none'',
 392 ``odd'', ``even'', ``mark'', or ``space''.  \fIData\fR is the number of
 393 data bits and should be an integer from 5 to 8, while \fIstop\fR is the
 394 number of stop bits and should be the integer 1 or 2.
 395 .TP
 396 \fB\-pollinterval \fImsec\fR
 397 .
 398 This option, available only on Windows for serial ports, is used to
 399 set the maximum time between polling for fileevents.  This affects the
 400 time interval between checking for events throughout the Tcl
 401 interpreter (the smallest value always wins).  Use this option only if
 402 you want to poll the serial port more often than 10 msec (the default).
 403 .TP
 404 \fB\-lasterror\fR
 405 .
 406 This option is available only on Windows for serial ports, and is
 407 query only (will only be reported when directly requested).
 408 In case of a serial communication error, \fBread\fR or \fBputs\fR
 409 returns a general Tcl file I/O error.
 410 \fBfconfigure -lasterror\fR can be called to get a list
 411 of error details (e.g. FRAME RXOVER).
 412 .VE
 413
 414 .VS
 415 .SH "PORTABILITY ISSUES"
 416 .sp
 417 .TP
 418 \fBWindows \fR(all versions)
 419 .
 420 Valid values for \fIfileName\fR to open a serial port are of the form
 421 \fBcom\fIX\fB:\fR, where \fIX\fR is a number, generally from 1 to 4.
 422 This notation only works for serial ports from 1 to 9, if the system
 423 happens to have more than four.  An attempt to open a serial port that
 424 does not exist or has a number greater than 9 will fail.  An alternate
 425 form of opening serial ports is to use the filename \fB\e\e.\ecomX\fR,
 426 where X is any number that corresponds to a serial port; please note
 427 that this method is considerably slower on Windows 95 and Windows 98.
 428 .TP
 429 \fBWindows NT\fR
 430 .
 431 When running Tcl interactively, there may be some strange interactions
 432 between the real console, if one is present, and a command pipeline that uses
 433 standard input or output.  If a command pipeline is opened for reading, some
 434 of the lines entered at the console will be sent to the command pipeline and
 435 some will be sent to the Tcl evaluator.  If a command pipeline is opened for
 436 writing, keystrokes entered into the console are not visible until the the
 437 pipe is closed.  This behavior occurs whether the command pipeline is
 438 executing 16-bit or 32-bit applications.  These problems only occur because
 439 both Tcl and the child application are competing for the console at
 440 the same time.  If the command pipeline is started from a script, so that Tcl
 441 is not accessing the console, or if the command pipeline does not use
 442 standard input or output, but is redirected from or to a file, then the
 443 above problems do not occur.
 444 .TP
 445 \fBWindows 95\fR
 446 .
 447 A command pipeline that executes a 16-bit DOS application cannot be opened
 448 for both reading and writing, since 16-bit DOS applications that receive
 449 standard input from a pipe and send standard output to a pipe run
 450 synchronously.  Command pipelines that do not execute 16-bit DOS
 451 applications run asynchronously and can be opened for both reading and
 452 writing.
 453 .sp
 454 When running Tcl interactively, there may be some strange interactions
 455 between the real console, if one is present, and a command pipeline that uses
 456 standard input or output.  If a command pipeline is opened for reading from
 457 a 32-bit application, some of the keystrokes entered at the console will be
 458 sent to the command pipeline and some will be sent to the Tcl evaluator.  If
 459 a command pipeline is opened for writing to a 32-bit application, no output
 460 is visible on the console until the the pipe is closed.  These problems only
 461 occur because both Tcl and the child application are competing for the
 462 console at the same time.  If the command pipeline is started from a script,
 463 so that Tcl is not accessing the console, or if the command pipeline does
 464 not use standard input or output, but is redirected from or to a file, then
 465 the above problems do not occur.
 466 .sp
 467 Whether or not Tcl is running interactively, if a command pipeline is opened
 468 for reading from a 16-bit DOS application, the call to \fBopen\fR will not
 469 return until end-of-file has been received from the command pipeline's
 470 standard output.  If a command pipeline is opened for writing to a 16-bit DOS
 471 application, no data will be sent to the command pipeline's standard output
 472 until the pipe is actually closed.  This problem occurs because 16-bit DOS
 473 applications are run synchronously, as described above.
 474 .TP
 475 \fBMacintosh\fR
 476 .
 477 Opening a serial port is not currently implemented under Macintosh.
 478 .sp
 479 Opening a command pipeline is not supported under Macintosh, since
 480 applications do not support the concept of standard input or output.
 481 .TP
 482 \fBUnix\fR\0\0\0\0\0\0\0
 483 .
 484 Valid values for \fIfileName\fR to open a serial port are generally of the
 485 form \fB/dev/tty\fIX\fR, where \fIX\fR is \fBa\fR or \fBb\fR, but the name
 486 of any pseudo-file that maps to a serial port may be used.
 487 .sp
 488 When running Tcl interactively, there may be some strange interactions
 489 between the console, if one is present, and a command pipeline that uses
 490 standard input.  If a command pipeline is opened for reading, some
 491 of the lines entered at the console will be sent to the command pipeline and
 492 some will be sent to the Tcl evaluator.  This problem only occurs because
 493 both Tcl and the child application are competing for the console at the
 494 same time.  If the command pipeline is started from a script, so that Tcl is
 495 not accessing the console, or if the command pipeline does not use standard
 496 input, but is redirected from a file, then the above problem does not occur.
 497 .LP
 498 See the PORTABILITY ISSUES section of the \fBexec\fR command for additional
 499 information not specific to command pipelines about executing
 500 applications on the various platforms
 501
 502 .SH "SEE ALSO"
 503 file(n), close(n), filename(n), fconfigure(n), gets(n), read(n),
 504 puts(n), exec(n), fopen(1)
 505
 506 .SH KEYWORDS
 507 access mode, append, create, file, non-blocking, open, permissions,
 508 pipeline, process, serial