Tcl Built-In Commands open(1T)
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NAME
open - Open a file-based or command pipeline channel
SYNOPSIS
open fileName
open fileName access
open fileName access permissions
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DESCRIPTION
This command opens a file, serial port, or command pipeline
and returns a channel identifier that may be used in future invocations of commands like read, puts, and close. If thefirst character of fileName is not | then the command opens
a file: fileName gives the name of the file to open, and it
must conform to the conventions described in the filename manual entry. The access argument, if present, indicates the way in which the file (or command pipeline) is to be accessed. In the first form access may have any of the following values: r Open the file for reading only; the file must already exist. This is the default value if access is not specified. r+ Open the file for both reading and writing; the file must already exist. w Open the file for writing only. Truncate it if it exists. If it doesn't exist, create a new file.w+ Open the file for reading and writing. Trun-
cate it if it exists. If it doesn't exist, create a new file. a Open the file for writing only. If the file doesn't exist, create a new empty file. Set the file pointer to the end of the file prior to each write. a+ Open the file for reading and writing. If the file doesn't exist, create a new empty file. Set the initial access position to the end of the file. In the second form, access consists of a list of any of the following flags, all of which have the standard POSIX Tcl Last change: 8.3 1Tcl Built-In Commands open(1T)
meanings. One of the flags must be either RDONLY, WRONLY or RDWR. RDONLY Open the file for reading only. WRONLY Open the file for writing only. RDWR Open the file for both reading and writing. APPEND Set the file pointer to the end of the file prior to each write. CREAT Create the file if it doesn't already exist (without this flag it is an error for the file not to exist). EXCL If CREAT is also specified, an error is returned if the file already exists. NOCTTY If the file is a terminal device, this flagprevents the file from becoming the control-
ling terminal of the process. NONBLOCK Prevents the process from blocking whileopening the file, and possibly in subsequent
I/O operations. The exact behavior of this
flag is system- and device-dependent; its
use is discouraged (it is better to use thefconfigure command to put a file in nonblock-
ing mode). For details refer to your systemdocumentation on the open system call's
O_NONBLOCK flag.
TRUNC If the file exists it is truncated to zero length.If a new file is created as part of opening it, permissions
(an integer) is used to set the permissions for the new file in conjunction with the process's file mode creation mask. Permissions defaults to 0666. Note that if you are going to be reading or writing binary data from the channel created by this command, you shoulduse the fconfigure command to change the -translation option
of the channel to binary before transferring any binary data. This is in contrast to the ``b'' character passed aspart of the equivalent of the access parameter to some ver-
sions of the C library fopen() function.
COMMAND PIPELINES Tcl Last change: 8.3 2Tcl Built-In Commands open(1T)
If the first character of fileName is ``|'' then the remain-
ing characters of fileName are treated as a list of argu-
ments that describe a command pipeline to invoke, in the same style as the arguments for exec. In this case, thechannel identifier returned by open may be used to write to
the command's input pipe or read from its output pipe,depending on the value of access. If write-only access is
used (e.g. access is w), then standard output for the pipe-
line is directed to the current standard output unless over-
ridden by the command. If read-only access is used (e.g.
access is r), 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 pidcommand, using the channel id returned by open as argument.
If the command (or one of the commands) executed in the com-
mand pipeline returns an error (according to the definition in exec), a Tcl error is generated when close is called onthe channel unless the pipeline is in non-blocking mode then
no exit status is returned (a silent close with -blocking
0).It is often useful to use the fileevent command with pipe-
lines so other processing may happen at the same time as running the command in the background. | SERIAL COMMUNICATIONS | If fileName refers to a serial port, then the specified |serial port is opened and initialized in a platform- |
dependent manner. Acceptable values for the fileName to use |to open a serial port are described in the PORTABILITY |
ISSUES section. |The fconfigure command can be used to query and set addi- |
tional configuration options specific to serial ports (where | supported): |-mode baud,parity,data,stop ||
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 baud rate is a | simple integer that specifies the connection speed. | Parity is one of the following letters: n, o, e, m, s; | respectively signifying the parity options of ``none'', | ``odd'', ``even'', ``mark'', or ``space''. Data is the | number of data bits and should be an integer from 5 to | 8, while stop is the number of stop bits and should be | the integer 1 or 2. |-handshake type ||
(Windows and Unix). This option is used to setup | automatic handshake control. Note that not all | Tcl Last change: 8.3 3Tcl Built-In Commands open(1T)
handshake types maybe supported by your operating sys- |
tem. The type parameter is case-independent. |
If type is none then any handshake is switched off. | rtscts activates hardware handshake. Hardware handshake | signals are described below. For software handshake | xonxoff the handshake characters can be redefined with |-xchar. An additional hardware handshake dtrdsr is |
available only under Windows. There is no default | handshake configuration, the initial value depends on |your operating system settings. The -handshake option |
cannot be queried. |-queue ||
(Windows and Unix). The -queue option can only be |
queried. It returns a list of two integers represent- |
ing the current number of bytes in the input and output | queue respectively. |-timeout msec ||
(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 -timeout option does not affect |
write operations or nonblocking reads. This option | cannot be queried. |-ttycontrol {signal boolean signal boolean ...} ||
(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 signal names |are case-independent. {RTS 1 DTR 0} sets the RTS out- |
put to high and the DTR output to low. The BREAK con- |
dition (see below) is enabled and disabled with {BREAK | 1} and {BREAK 0} respectively. It's not a good idea to | change the RTS (or DTR) signal with active hardware |handshake rtscts (or dtrdsr). The result is unpredict- |
able. The -ttycontrol option cannot be queried. |
-ttys- |
tatus ||(Windows and Unix). The -ttystatus 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. | {CTS 1 DSR 0 RING 1 DCD 0}. The signal names are | returned upper case. |-xchar {xonChar xoffChar} ||
(Windows and Unix). This option is used to query or | change the software handshake characters. Normally the | Tcl Last change: 8.3 4Tcl Built-In Commands open(1T)
operating system default should be DC1 (0x11) and DC3 | (0x13) representing the ASCII standard XON and XOFF | characters. |-pollinterval msec ||
(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 or less often than 10 msec (the default). |-sysbuffer inSize ||
-sysbuffer {inSize outSize} ||
(Windows only). This option is used to change the size |of Windows system buffers for a serial channel. Espe- |
cially at higher communication rates the default input |buffer size of 4096 bytes can overrun for latent sys- |
tems. The first form specifies the input buffer size, | in the second form both input and output buffers are | defined. |-laster- |
ror || (Windows only). This option is query only. In case of | a serial communication error, read or puts returns a |general Tcl file I/O error. fconfigure -lasterror can |
be called to get a list of error details. See below | for an explanation of the various error codes. | SERIAL PORT SIGNALS |RS-232 is the most commonly used standard electrical inter- |
face 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 fol- |
lowing signals are specified for incoming and outgoing data, | status lines and handshaking. Here we are using the terms | workstation for your computer and modem 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. | TXD(output) || Transmitted Data: Outgoing serial data. | RXD(input) || Received Data:Incoming serial data. | RTS(output) || Tcl Last change: 8.3 5Tcl Built-In Commands open(1T)
Request To Send: 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. | CTS(input) || Clear To Send: The complement to RTS. Indicates that | the modem is ready to receive data. | DTR(output) || Data Terminal Ready: 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. |
DSR(input) ||Data Set Ready: The complement to DTR. Tells the works- |
tation that the modem is ready to establish a link. | DCD(input) || Data Carrier Detect: This line becomes active when a | modem detects a "Carrier" signal. | RI(input) || Ring Indicator: Goes active when the modem detects an | incoming call. | BREAK || 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. |ERROR CODES (Windows only) |
A lot of different errors may occur during serial read |operations or during event polling in background. The exter- |
nal device may have been switched off, the data lines may be | noisy, system buffers may overrun or your mode settings may | be wrong. That's why a reliable software should always | catch serial read operations. In cases of an error Tcl |returns a general file I/O error. Then fconfigure -laster- |
ror may help to locate the problem. The following error | codes may be returned. | RXOVER || Windows input buffer overrun. The data comes | Tcl Last change: 8.3 6Tcl Built-In Commands open(1T)
faster than your scripts reads it or your system |is overloaded. Use fconfigure -sysbuffer to avoid |
a temporary bottleneck and/or make your script | faster. | TXFULL || Windows output buffer overrun. Complement to | RXOVER. This error should practically not happen, | because Tcl cares about the output buffer status. |OVER- |
RUN || UART buffer overrun (hardware) with data lost. | The data comes faster than the system driver |receives it. Check your advanced serial port set- |
tings to enable the FIFO (16550) buffer and/or | setup a lower(1) interrupt threshold value. |RXPAR- |
ITY || A parity error has been detected by your UART. |Wrong parity settings with fconfigure -mode or a |
noisy data line (RXD) may cause this error. | FRAME ||A stop-bit error has been detected by your UART. |
Wrong mode settings with fconfigure -mode or a |
noisy data line (RXD) may cause this error. | BREAK || A BREAK condition has been detected by your UART | (see above). PORTABILITY ISSUES Windows (all versions)Valid values for fileName to open a serial port are of
the form comX:, where X is a number, generally from 1 to 4. This notation only works for serial ports from 1 to 9, if the system happens to have more than four. Anattempt to open a serial port that does not exist or
has a number greater than 9 will fail. An alternateform of opening serial ports is to use the filename
\\.\comX, where X is any number that corresponds to aserial port; please note that this method is consider-
ably slower on Windows 95 and Windows 98. Windows NT When running Tcl interactively, there may be some strange interactions between the real console, if one is present, and a command pipeline that uses standardinput or output. If a command pipeline is opened for
Tcl Last change: 8.3 7Tcl Built-In Commands open(1T)
reading, some of the lines entered at the console will be sent to the command pipeline and some will be sentto the Tcl evaluator. If a command pipeline is opened
for writing, keystrokes entered into the console are not visible until the pipe is closed. This behavioroccurs whether the command pipeline is executing 16-bit
or 32-bit applications. These problems only occur
because both Tcl and the child application are compet-
ing 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. Windows 95A command pipeline that executes a 16-bit DOS applica-
tion cannot be opened for both reading and writing,
since 16-bit DOS applications that receive standard
input from a pipe and send standard output to a piperun synchronously. Command pipelines that do not exe-
cute 16-bit DOS applications run asynchronously and can
be opened for both reading and writing.
When running Tcl interactively, there may be some strange interactions between the real console, if one is present, and a command pipeline that uses standardinput or output. If a command pipeline is opened for
reading from a 32-bit application, some of the keys-
trokes entered at the console will be sent to the com-
mand pipeline and some will be sent to the Tcl evalua-
tor. If a command pipeline is opened for writing to a
32-bit application, no output is visible on the console
until the pipe is closed. These problems only occurbecause both Tcl and the child application are compet-
ing 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.Whether or not Tcl is running interactively, if a com-
mand pipeline is opened for reading from a 16-bit DOS
application, the call to open will not return until
end-of-file has been received from the command
pipeline's standard output. If a command pipeline isopened 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 occursbecause 16-bit DOS applications are run synchronously,
as described above. Tcl Last change: 8.3 8Tcl Built-In Commands open(1T)
Macintosh Opening a serial port is not currently implemented under Macintosh. Opening a command pipeline is not supported underMacintosh, since applications do not support the con-
cept of standard input or output. UnixValid values for fileName to open a serial port are
generally of the form /dev/ttyX, where X is a or b, butthe name of any pseudo-file that maps to a serial port
may be used. Advanced configuration options are only | supported for serial ports when Tcl is built to use the | POSIX serial interface. When running Tcl interactively, there may be some strange interactions between the console, if one is present, and a command pipeline that uses standardinput. 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. This problem only occurs 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 theconsole, or if the command pipeline does not use stan-
dard input, but is redirected from a file, then the above problem does not occur. See the PORTABILITY ISSUES section of the exec command for additional information not specific to command pipelines about executing applications on the various platformsEXAMPLE
Open a command pipeline and catch any errors:set fl [open "| ls this_file_does_not_exist"]
set data [read $fl]
if {[catch {close $fl} err]} {
puts "ls command failed: $err"
}SEE ALSO
file(1T), close(1T), filename(1T), fconfigure(1T), gets(1T),read(1T), puts(1T), exec(1T), pid(1T), fopen(3TCL)
KEYWORDSaccess mode, append, create, file, non-blocking, open, per-
missions, pipeline, process, serial Tcl Last change: 8.3 9Tcl Built-In Commands open(1T)
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:_______________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE|
|____________________|__________________|_
| Availability | runtime/tcl-8 |
|____________________|__________________|_
| Interface Stability| Uncommitted ||____________________|_________________|
NOTESSource for Tcl is available on http://opensolaris.org.
Tcl Last change: 8.3 10