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.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

open \- Open a file-based or command pipeline channel

.SH SYNOPSIS

.sp

\fBopen \fIfileName\fR

.br

\fBopen \fIfileName access\fR

.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

the command opens a file:

\fIfileName\fR gives the name of the file to open, and it must conform to the

conventions described in the \fBfilename\fR manual entry.

.PP

The \fIaccess\fR argument, if present, indicates the way in which the file

(or command pipeline) is to be accessed.

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

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.

.TP 15

\fBa\fR

Open the file for writing only.  The file must already exist, and the file

is positioned so that new data is appended to the file.

.TP 15

\fBa+\fR

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.

.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

\fBCREAT\fR

Create the file if it doesn't 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

(it is better to use the \fBfconfigure\fR command to put a file

in nonblocking mode).

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.

.SH "COMMAND PIPELINES"

.PP

If the first character of \fIfileName\fR is ``|'' 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

output unless overridden by the command.

If read-only access is used (e.g. \fIaccess\fR is \fBr\fR),

standard input for the pipeline is taken from the current standard

input unless overridden by the command.

.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:

.TP

\fB\-mode \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

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.

.VE

.VS

.SH "PORTABILITY ISSUES"

.sp

.TP

\fBWindows \fR(all versions)

.

Valid values for \fIfileName\fR to open a serial port are of the form

\fBcom\fIX\fB:\fR, where \fIX\fR is a number, generally from 1 to 4.  An

attempt to open a serial port that does not exist will fail.

.TP

\fBWindows NT\fR

.

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, 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

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

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.

.TP

\fBWindows 95\fR

.

A command pipeline that executes a 16-bit DOS application 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 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

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

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

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

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

\fBWindows 3.X\fR

.

A command pipeline can execute 16-bit or 32-bit DOS or Windows

applications, but the call to \fBopen\fR will not return until the last

program in the pipeline has finished executing; command pipelines run

synchronously.  If the pipeline is opened with write access (either just

writing or both reading and writing) the first application in the

pipeline will instead see an immediate end-of-file; any data the caller

writes to the open pipe will instead be discarded.

.sp

Since Tcl cannot be run with a real console under Windows 3.X, there are

no interactions between command pipelines and the console.

.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.

.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

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

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 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

applications on the various platforms

.SH "SEE ALSO"

close(n), filename(n), gets(n), read(n), puts(n), exec(n)

.VE

.SH KEYWORDS

access mode, append, create, file, non-blocking, open, permissions,

pipeline, process, serial