'\"
'\" Copyright (c) 1993 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\" Copyright (c) 2006 Donal K. Fellows.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\" 
'\" RCS: @(#) $Id: exec.n,v 1.6.4.8 2007/11/01 16:55:54 dgp Exp $
'\" RCS: @(#) $Id: exec.n,v 1.6.4.9 2008/06/30 13:34:59 dgp Exp $
'\" 
.so man.macros
.TH exec n 8.5 Tcl "Tcl Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
exec \- Invoke subprocesses
.SH SYNOPSIS
\fBexec \fR?\fIswitches\fR? \fIarg \fR?\fIarg ...\fR?
.BE

.SH DESCRIPTION
.PP
This command treats its arguments as the specification
of one or more subprocesses to execute.
The arguments take the form of a standard shell pipeline
where each \fIarg\fR becomes one word of a command, and
each distinct command becomes a subprocess.
.PP
If the initial arguments to \fBexec\fR start with \fB\-\fR then
they are treated as command-line switches and are not part
of the pipeline specification.  The following switches are
currently supported:
.TP 13
\fB\-ignorestderr\fR
.VS 8.5
.
Stops the \fBexec\fR command from treating the output of messages to the
pipeline's standard error channel as an error case.
.VE 8.5
.TP 13
\fB\-keepnewline\fR
.
Retains a trailing newline in the pipeline's output.
Normally a trailing newline will be deleted.
.TP 13
\fB\-\|\-\fR
.
Marks the end of switches.  The argument following this one will
be treated as the first \fIarg\fR even if it starts with a \fB\-\fR.
.PP
If an \fIarg\fR (or pair of \fIarg\fRs) has one of the forms
described below then it is used by \fBexec\fR to control the
flow of input and output among the subprocess(es).
Such arguments will not be passed to the subprocess(es).  In forms
such as
.QW "\fB<\fR \fIfileName\fR" ,
\fIfileName\fR may either be in a separate argument from
.QW \fB<\fR
or in the same argument with no intervening space (i.e.
.QW \fB<\fIfileName\fR ).
.TP 15
\fB|\fR
.
Separates distinct commands in the pipeline.  The standard output
of the preceding command will be piped into the standard input
of the next command.
.TP 15
\fB|&\fR
.
Separates distinct commands in the pipeline.  Both standard output
and standard error of the preceding command will be piped into
the standard input of the next command.
This form of redirection overrides forms such as 2> and >&.
.TP 15
\fB<\0\fIfileName\fR
.
The file named by \fIfileName\fR is opened and used as the standard
input for the first command in the pipeline.
.TP 15
\fB<@\0\fIfileId\fR
.
\fIFileId\fR must be the identifier for an open file, such as the return
value from a previous call to \fBopen\fR.
It is used as the standard input for the first command in the pipeline.
\fIFileId\fR must have been opened for reading.
.TP 15
\fB<<\0\fIvalue\fR
.
\fIValue\fR is passed to the first command as its standard input.
.TP 15
\fB>\0\fIfileName\fR
.
Standard output from the last command is redirected to the file named
\fIfileName\fR, overwriting its previous contents.
.TP 15
\fB2>\0\fIfileName\fR
.
Standard error from all commands in the pipeline is redirected to the
file named \fIfileName\fR, overwriting its previous contents.
.TP 15
\fB>&\0\fIfileName\fR
.
Both standard output from the last command and standard error from all
commands are redirected to the file named \fIfileName\fR, overwriting
its previous contents.
.TP 15
\fB>>\0\fIfileName\fR
.
Standard output from the last command is
redirected to the file named \fIfileName\fR, appending to it rather
than overwriting it.
.TP 15
\fB2>>\0\fIfileName\fR
.
Standard error from all commands in the pipeline is
redirected to the file named \fIfileName\fR, appending to it rather
than overwriting it.
.TP 15
\fB>>&\0\fIfileName\fR
.
Both standard output from the last command and standard error from
all commands are redirected to the file named \fIfileName\fR,
appending to it rather than overwriting it.
.TP 15
\fB>@\0\fIfileId\fR
.
\fIFileId\fR must be the identifier for an open file, such as the return
value from a previous call to \fBopen\fR.
Standard output from the last command is redirected to \fIfileId\fR's
file, which must have been opened for writing.
.TP 15
\fB2>@\0\fIfileId\fR
.
\fIFileId\fR must be the identifier for an open file, such as the return
value from a previous call to \fBopen\fR.
Standard error from all commands in the pipeline is
redirected to \fIfileId\fR's file.
The file must have been opened for writing.
.TP 15
\fB2>@1\0\fR
.
Standard error from all commands in the pipeline is redirected to the
command result.  This operator is only valid at the end of the command
pipeline.
.TP 15
\fB>&@\0\fIfileId\fR
.
\fIFileId\fR must be the identifier for an open file, such as the return
value from a previous call to \fBopen\fR.
Both standard output from the last command and standard error from
all commands are redirected to \fIfileId\fR's file.
The file must have been opened for writing.
.PP
If standard output has not been redirected then the \fBexec\fR
command returns the standard output from the last command
in the pipeline,
in the pipeline, unless
.VS 8.5
unless
.QW 2>@1
was specified, in which case standard error is included as well.
.VE 8.5
If any of the commands in the pipeline exit abnormally or
are killed or suspended, then \fBexec\fR will return an error
and the error message will include the pipeline's output followed by
error messages describing the abnormal terminations; the
\fB\-errorcode\fR return option will contain additional information
about the last abnormal termination encountered.
If any of the commands writes to its standard error file and that
standard error is not redirected
.VS 8.5
and \fB\-ignorestderr\fR is not specified,
.VE 8.5
then \fBexec\fR will return an error;  the error message
will include the pipeline's standard output, followed by messages
about abnormal terminations (if any), followed by the standard error
output.
.PP
If the last character of the result or error message
is a newline then that character is normally deleted

interactively.  Applications which directly access the console window,
rather than reading from their standard input and writing to their standard
output may fail, hang Tcl, or even hang the system if their own private
console window is not available to them.
.RE
.TP
\fBUnix\fR\0\0\0\0\0\0\0
.
The \fBexec\fR command is fully functional and works as described.
.SH "UNIX EXAMPLES"
Here are some examples of the use of the \fBexec\fR command on Unix.
.PP
To execute a simple program and get its result:
.CS
\fBexec\fR uname -a