diff options
Diffstat (limited to 'doc/open.n')
| -rw-r--r-- | doc/open.n | 326 |
1 files changed, 259 insertions, 67 deletions
@@ -5,10 +5,8 @@ '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" -'\" RCS: @(#) $Id: open.n,v 1.12 2000/12/08 11:22:54 dkf Exp $ -'\" +.TH open n 8.3 Tcl "Tcl Built-In Commands" .so man.macros -.TH open n 7.6 Tcl "Tcl Built-In Commands" .BS '\" Note: do not modify the .SH NAME line immediately below! .SH NAME @@ -21,12 +19,9 @@ open \- Open a file-based or command pipeline channel .br \fBopen \fIfileName access permissions\fR .BE - .SH DESCRIPTION .PP -.VS This command opens a file, serial port, or command pipeline and returns a -.VE channel identifier that may be used in future invocations of commands like \fBread\fR, \fBputs\fR, and \fBclose\fR. If the first character of \fIfileName\fR is not \fB|\fR then @@ -39,60 +34,84 @@ The \fIaccess\fR argument, if present, indicates the way in which the file In the first form \fIaccess\fR may have any of the following values: .TP 15 \fBr\fR +. Open the file for reading only; the file must already exist. This is the default value if \fIaccess\fR is not specified. .TP 15 \fBr+\fR +. Open the file for both reading and writing; the file must already exist. .TP 15 \fBw\fR -Open the file for writing only. Truncate it if it exists. If it doesn't +. +Open the file for writing only. Truncate it if it exists. If it does not exist, create a new file. .TP 15 \fBw+\fR +. Open the file for reading and writing. Truncate it if it exists. -If it doesn't exist, create a new file. +If it does not exist, create a new file. .TP 15 \fBa\fR -Open the file for writing only. If the file doesn't exist, +. +Open the file for writing only. If the file does not exist, create a new empty file. -Set the initial access position to the end of the file. +Set the file pointer to the end of the file prior to each write. .TP 15 \fBa+\fR -Open the file for reading and writing. If the file doesn't exist, +. +Open the file for reading and writing. If the file does not exist, create a new empty file. Set the initial access position to the end of the file. .PP +All of the legal \fIaccess\fR values above may have the character +\fBb\fR added as the second or third character in the value to +indicate that the opened channel should be configured as if with the +\fBfconfigure\fR \fB\-translation binary\fR option, making the channel suitable for +reading or writing of binary data. +.PP In the second form, \fIaccess\fR consists of a list of any of the following flags, all of which have the standard POSIX meanings. One of the flags must be either \fBRDONLY\fR, \fBWRONLY\fR or \fBRDWR\fR. .TP 15 \fBRDONLY\fR +. Open the file for reading only. .TP 15 \fBWRONLY\fR +. Open the file for writing only. .TP 15 \fBRDWR\fR +. Open the file for both reading and writing. .TP 15 \fBAPPEND\fR +. Set the file pointer to the end of the file prior to each write. .TP 15 +\fBBINARY\fR +. +Configure the opened channel with the \fB\-translation binary\fR option. +.TP 15 \fBCREAT\fR -Create the file if it doesn't already exist (without this flag it +. +Create the file if it does not already exist (without this flag it is an error for the file not to exist). .TP 15 \fBEXCL\fR +. If \fBCREAT\fR is also specified, an error is returned if the file already exists. .TP 15 \fBNOCTTY\fR +. If the file is a terminal device, this flag prevents the file from becoming the controlling terminal of the process. .TP 15 \fBNONBLOCK\fR +. Prevents the process from blocking while opening the file, and possibly in subsequent I/O operations. The exact behavior of this flag is system- and device-dependent; its use is discouraged @@ -102,83 +121,245 @@ For details refer to your system documentation on the \fBopen\fR system call's \fBO_NONBLOCK\fR flag. .TP 15 \fBTRUNC\fR +. If the file exists it is truncated to zero length. .PP If a new file is created as part of opening it, \fIpermissions\fR (an integer) is used to set the permissions for the new file in conjunction with the process's file mode creation mask. \fIPermissions\fR defaults to 0666. -.PP -'\" Not versioned as advice applies to all recent versions of Tcl. -'\" Prior to that, Tcl didn't really support binary files anyway... -.VS -Note that if you are going to be reading or writing binary data from -the channel created by this command, you should use the -\fBfconfigure\fR command to change the \fB-translation\fR option of -the channel to \fBbinary\fR before transferring any binary data. This -is in contrast to the ``b'' character passed as part of the equivalent -of the \fIaccess\fR parameter to some versions of the C library -\fIfopen()\fR function. -.VE .SH "COMMAND PIPELINES" .PP -If the first character of \fIfileName\fR is ``|'' then the +If the first character of \fIfileName\fR is +.QW \fB|\fR +then the remaining characters of \fIfileName\fR are treated as a list of arguments that describe a command pipeline to invoke, in the same style as the arguments for \fBexec\fR. In this case, the channel identifier returned by \fBopen\fR may be used to write to the command's input pipe or read from its output pipe, depending on the value of \fIaccess\fR. -If write-only access is used (e.g. \fIaccess\fR is \fBw\fR), then -standard output for the pipeline is directed to the current standard +If write-only access is used (e.g. \fIaccess\fR is +.QW \fBw\fR ), +then standard output for the pipeline is directed to the current standard output unless overridden by the command. -If read-only access is used (e.g. \fIaccess\fR is \fBr\fR), +If read-only access is used (e.g. \fIaccess\fR is +.QW \fBr\fR ), standard input for the pipeline is taken from the current standard input unless overridden by the command. +The id of the spawned process is accessible through the \fBpid\fR +command, using the channel id returned by \fBopen\fR as argument. +.PP +If the command (or one of the commands) executed in the command +pipeline returns an error (according to the definition in \fBexec\fR), +a Tcl error is generated when \fBclose\fR is called on the channel +unless the pipeline is in non-blocking mode then no exit status is +returned (a silent \fBclose\fR with -blocking 0). +.PP +It is often useful to use the \fBfileevent\fR command with pipelines +so other processing may happen at the same time as running the command +in the background. .SH "SERIAL COMMUNICATIONS" -.VS .PP If \fIfileName\fR refers to a serial port, then the specified serial port is opened and initialized in a platform-dependent manner. Acceptable values for the \fIfileName\fR to use to open a serial port are described in the PORTABILITY ISSUES section. - -.SH "CONFIGURATION OPTIONS" -The \fBfconfigure\fR command can be used to query and set the following -configuration option for open serial ports: +.PP +The \fBfconfigure\fR command can be used to query and set additional +configuration options specific to serial ports (where supported): .TP -\fB\-mode \fIbaud\fB,\fIparity\fB,\fIdata\fB,\fIstop\fR +\fB\-mode\fR \fIbaud\fB,\fIparity\fB,\fIdata\fB,\fIstop\fR . This option is a set of 4 comma-separated values: the baud rate, parity, number of data bits, and number of stop bits for this serial port. The \fIbaud\fR rate is a simple integer that specifies the connection speed. \fIParity\fR is one of the following letters: \fBn\fR, \fBo\fR, \fBe\fR, -\fBm\fR, \fBs\fR; respectively signifying the parity options of ``none'', -``odd'', ``even'', ``mark'', or ``space''. \fIData\fR is the number of +\fBm\fR, \fBs\fR; respectively signifying the parity options of +.QW none , +.QW odd , +.QW even , +.QW mark , +or +.QW space . +\fIData\fR is the number of data bits and should be an integer from 5 to 8, while \fIstop\fR is the number of stop bits and should be the integer 1 or 2. .TP -\fB\-pollinterval \fImsec\fR +\fB\-handshake\fR \fItype\fR +. +(Windows and Unix). This option is used to setup automatic handshake +control. Note that not all handshake types maybe supported by your operating +system. The \fItype\fR parameter is case-independent. +.RS +.PP +If \fItype\fR is \fBnone\fR then any handshake is switched off. +\fBrtscts\fR activates hardware handshake. Hardware handshake signals +are described below. +For software handshake \fBxonxoff\fR the handshake characters can be redefined +with \fB\-xchar\fR. +An additional hardware handshake \fBdtrdsr\fR is available only under Windows. +There is no default handshake configuration, the initial value depends +on your operating system settings. +The \fB\-handshake\fR option cannot be queried. +.RE +.TP +\fB\-queue\fR +. +(Windows and Unix). The \fB\-queue\fR option can only be queried. +It returns a list of two integers representing the current number +of bytes in the input and output queue respectively. +.TP +\fB\-timeout\fR \fImsec\fR +. +(Windows and Unix). This option is used to set the timeout for blocking +read operations. It specifies the maximum interval between the +reception of two bytes in milliseconds. +For Unix systems the granularity is 100 milliseconds. +The \fB\-timeout\fR option does not affect write operations or +nonblocking reads. +This option cannot be queried. +.TP +\fB\-ttycontrol\fR \fI{signal boolean signal boolean ...}\fR +. +(Windows and Unix). This option is used to setup the handshake +output lines (see below) permanently or to send a BREAK over the serial line. +The \fIsignal\fR names are case-independent. +\fB{RTS 1 DTR 0}\fR sets the RTS output to high and the DTR output to low. +The BREAK condition (see below) is enabled and disabled with \fB{BREAK 1}\fR and +\fB{BREAK 0}\fR respectively. +It is not a good idea to change the \fBRTS\fR (or \fBDTR\fR) signal +with active hardware handshake \fBrtscts\fR (or \fBdtrdsr\fR). +The result is unpredictable. +The \fB\-ttycontrol\fR option cannot be queried. +.TP +\fB\-ttystatus\fR +. +(Windows and Unix). The \fB\-ttystatus\fR option can only be +queried. It returns the current modem status and handshake input signals +(see below). +The result is a list of signal,value pairs with a fixed order, +e.g. \fB{CTS 1 DSR 0 RING 1 DCD 0}\fR. +The \fIsignal\fR names are returned upper case. +.TP +\fB\-xchar\fR \fI{xonChar xoffChar}\fR +. +(Windows and Unix). This option is used to query or change the software +handshake characters. Normally the operating system default should be +DC1 (0x11) and DC3 (0x13) representing the ASCII standard +XON and XOFF characters. +.TP +\fB\-pollinterval\fR \fImsec\fR . -This option, available only on Windows for serial ports, is used to -set the maximum time between polling for fileevents. This affects the -time interval between checking for events throughout the Tcl +(Windows only). This option is used to set the maximum time between +polling for fileevents. +This affects the time interval between checking for events throughout the Tcl interpreter (the smallest value always wins). Use this option only if -you want to poll the serial port more often than 10 msec (the default). +you want to poll the serial port more or less often than 10 msec +(the default). +.TP +\fB\-sysbuffer\fR \fIinSize\fR +.TP +\fB\-sysbuffer\fR \fI{inSize outSize}\fR +. +(Windows only). This option is used to change the size of Windows +system buffers for a serial channel. Especially at higher communication +rates the default input buffer size of 4096 bytes can overrun +for latent systems. The first form specifies the input buffer size, +in the second form both input and output buffers are defined. .TP \fB\-lasterror\fR . -This option is available only on Windows for serial ports, and is -query only (will only be reported when directly requested). +(Windows only). This option is query only. In case of a serial communication error, \fBread\fR or \fBputs\fR returns a general Tcl file I/O error. -\fBfconfigure -lasterror\fR can be called to get a list -of error details (e.g. FRAME RXOVER). -.VE - -.VS +\fBfconfigure\fR \fB\-lasterror\fR can be called to get a list of error details. +See below for an explanation of the various error codes. +.SH "SERIAL PORT SIGNALS" +.PP +RS-232 is the most commonly used standard electrical interface for serial +communications. A negative voltage (-3V..-12V) define a mark (on=1) bit and +a positive voltage (+3..+12V) define a space (off=0) bit (RS-232C). The +following signals are specified for incoming and outgoing data, status +lines and handshaking. Here we are using the terms \fIworkstation\fR for +your computer and \fImodem\fR for the external device, because some signal +names (DCD, RI) come from modems. Of course your external device may use +these signal lines for other purposes. +.IP \fBTXD\fR(output) +\fBTransmitted Data:\fR Outgoing serial data. +.IP \fBRXD\fR(input) +\fBReceived Data:\fRIncoming serial data. +.IP \fBRTS\fR(output) +\fBRequest To Send:\fR This hardware handshake line informs the modem that +your workstation is ready to receive data. Your workstation may +automatically reset this signal to indicate that the input buffer is full. +.IP \fBCTS\fR(input) +\fBClear To Send:\fR The complement to RTS. Indicates that the modem is +ready to receive data. +.IP \fBDTR\fR(output) +\fBData Terminal Ready:\fR This signal tells the modem that the workstation +is ready to establish a link. DTR is often enabled automatically whenever a +serial port is opened. +.IP \fBDSR\fR(input) +\fBData Set Ready:\fR The complement to DTR. Tells the workstation that the +modem is ready to establish a link. +.IP \fBDCD\fR(input) +\fBData Carrier Detect:\fR This line becomes active when a modem detects a +.QW Carrier +signal. +.IP \fBRI\fR(input) +\fBRing Indicator:\fR Goes active when the modem detects an incoming call. +.IP \fBBREAK\fR +A BREAK condition is not a hardware signal line, but a logical zero on the +TXD or RXD lines for a long period of time, usually 250 to 500 +milliseconds. Normally a receive or transmit data signal stays at the mark +(on=1) voltage until the next character is transferred. A BREAK is sometimes +used to reset the communications line or change the operating mode of +communications hardware. +.SH "ERROR CODES (Windows only)" +.PP +A lot of different errors may occur during serial read operations or during +event polling in background. The external device may have been switched +off, the data lines may be noisy, system buffers may overrun or your mode +settings may be wrong. That is why a reliable software should always +\fBcatch\fR serial read operations. In cases of an error Tcl returns a +general file I/O error. Then \fBfconfigure\fR \fB\-lasterror\fR may help to +locate the problem. The following error codes may be returned. +.TP 10 +\fBRXOVER\fR +. +Windows input buffer overrun. The data comes faster than your scripts reads +it or your system is overloaded. Use \fBfconfigure\fR \fB\-sysbuffer\fR to avoid a +temporary bottleneck and/or make your script faster. +.TP 10 +\fBTXFULL\fR +. +Windows output buffer overrun. Complement to RXOVER. This error should +practically not happen, because Tcl cares about the output buffer status. +.TP 10 +\fBOVERRUN\fR +. +UART buffer overrun (hardware) with data lost. +The data comes faster than the system driver receives it. +Check your advanced serial port settings to enable the FIFO (16550) buffer +and/or setup a lower(1) interrupt threshold value. +.TP 10 +\fBRXPARITY\fR +. +A parity error has been detected by your UART. +Wrong parity settings with \fBfconfigure\fR \fB\-mode\fR or a noisy data line (RXD) +may cause this error. +.TP 10 +\fBFRAME\fR +. +A stop-bit error has been detected by your UART. +Wrong mode settings with \fBfconfigure\fR \fB\-mode\fR or a noisy data line (RXD) +may cause this error. +.TP 10 +\fBBREAK\fR +. +A BREAK condition has been detected by your UART (see above). .SH "PORTABILITY ISSUES" -.sp .TP \fBWindows \fR(all versions) . @@ -198,7 +379,7 @@ between the real console, if one is present, and a command pipeline that uses standard input or output. If a command pipeline is opened for reading, some of the lines entered at the console will be sent to the command pipeline and some will be sent to the Tcl evaluator. If a command pipeline is opened for -writing, keystrokes entered into the console are not visible until the the +writing, keystrokes entered into the console are not visible until the pipe is closed. This behavior occurs whether the command pipeline is executing 16-bit or 32-bit applications. These problems only occur because both Tcl and the child application are competing for the console at @@ -215,20 +396,21 @@ standard input from a pipe and send standard output to a pipe run synchronously. Command pipelines that do not execute 16-bit DOS applications run asynchronously and can be opened for both reading and writing. -.sp +.RS +.PP When running Tcl interactively, there may be some strange interactions between the real console, if one is present, and a command pipeline that uses standard input or output. If a command pipeline is opened for reading from a 32-bit application, some of the keystrokes entered at the console will be sent to the command pipeline and some will be sent to the Tcl evaluator. If a command pipeline is opened for writing to a 32-bit application, no output -is visible on the console until the the pipe is closed. These problems only +is visible on the console until the pipe is closed. These problems only occur because both Tcl and the child application are competing for the console at the same time. If the command pipeline is started from a script, so that Tcl is not accessing the console, or if the command pipeline does not use standard input or output, but is redirected from or to a file, then the above problems do not occur. -.sp +.PP Whether or not Tcl is running interactively, if a command pipeline is opened for reading from a 16-bit DOS application, the call to \fBopen\fR will not return until end-of-file has been received from the command pipeline's @@ -236,20 +418,17 @@ standard output. If a command pipeline is opened for writing to a 16-bit DOS application, no data will be sent to the command pipeline's standard output until the pipe is actually closed. This problem occurs because 16-bit DOS applications are run synchronously, as described above. -.TP -\fBMacintosh\fR -. -Opening a serial port is not currently implemented under Macintosh. -.sp -Opening a command pipeline is not supported under Macintosh, since -applications do not support the concept of standard input or output. +.RE .TP \fBUnix\fR\0\0\0\0\0\0\0 . Valid values for \fIfileName\fR to open a serial port are generally of the form \fB/dev/tty\fIX\fR, where \fIX\fR is \fBa\fR or \fBb\fR, but the name of any pseudo-file that maps to a serial port may be used. -.sp +Advanced configuration options are only supported for serial ports +when Tcl is built to use the POSIX serial interface. +.RS +.PP When running Tcl interactively, there may be some strange interactions between the console, if one is present, and a command pipeline that uses standard input. If a command pipeline is opened for reading, some @@ -259,15 +438,28 @@ both Tcl and the child application are competing for the console at the same time. If the command pipeline is started from a script, so that Tcl is not accessing the console, or if the command pipeline does not use standard input, but is redirected from a file, then the above problem does not occur. -.LP -See the PORTABILITY ISSUES section of the \fBexec\fR command for additional -information not specific to command pipelines about executing +.RE +.PP +See the \fBPORTABILITY ISSUES\fR section of the \fBexec\fR command for +additional information not specific to command pipelines about executing applications on the various platforms - +.SH "EXAMPLE" +.PP +Open a command pipeline and catch any errors: +.PP +.CS +set fl [\fBopen\fR "| ls this_file_does_not_exist"] +set data [read $fl] +if {[catch {close $fl} err]} { + puts "ls command failed: $err" +} +.CE .SH "SEE ALSO" file(n), close(n), filename(n), fconfigure(n), gets(n), read(n), -puts(n), exec(n), fopen(1) - +puts(n), exec(n), pid(n), fopen(3) .SH KEYWORDS access mode, append, create, file, non-blocking, open, permissions, pipeline, process, serial +'\"Local Variables: +'\"mode: nroff +'\"End: |