186 lines
6.6 KiB
Plaintext
186 lines
6.6 KiB
Plaintext
'\"
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'\" Copyright (c) 1993 The Regents of the University of California.
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'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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'\" SCCS: @(#) exec.n 1.12 96/03/25 20:13:20
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'\"
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.so man.macros
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.TH exec n 7.0 Tcl "Tcl Built-In Commands"
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.BS
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'\" Note: do not modify the .SH NAME line immediately below!
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.SH NAME
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exec \- Invoke subprocess(es)
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.SH SYNOPSIS
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\fBexec \fR?\fIswitches\fR? \fIarg \fR?\fIarg ...\fR?
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.BE
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.SH DESCRIPTION
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.PP
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This command treats its arguments as the specification
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of one or more subprocesses to execute.
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The arguments take the form of a standard shell pipeline
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where each \fIarg\fR becomes one word of a command, and
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each distinct command becomes a subprocess.
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.PP
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If the initial arguments to \fBexec\fR start with \fB\-\fR then
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.VS
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they are treated as command-line switches and are not part
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of the pipeline specification. The following switches are
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currently supported:
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.TP 13
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\fB\-keepnewline\fR
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Retains a trailing newline in the pipeline's output.
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Normally a trailing newline will be deleted.
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.TP 13
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\fB\-\|\-\fR
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Marks the end of switches. The argument following this one will
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be treated as the first \fIarg\fR even if it starts with a \fB\-\fR.
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.VE
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.PP
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If an \fIarg\fR (or pair of \fIarg\fR's) has one of the forms
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described below then it is used by \fBexec\fR to control the
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flow of input and output among the subprocess(es).
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Such arguments will not be passed to the subprocess(es). In forms
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.VS
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such as ``< \fIfileName\fR'' \fIfileName\fR may either be in a
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separate argument from ``<'' or in the same argument with no
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intervening space (i.e. ``<\fIfileName\fR'').
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.VE
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.TP 15
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Separates distinct commands in the pipeline. The standard output
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of the preceding command will be piped into the standard input
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of the next command.
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.TP 15
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|&
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Separates distinct commands in the pipeline. Both standard output
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and standard error of the preceding command will be piped into
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the standard input of the next command.
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This form of redirection overrides forms such as 2> and >&.
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.TP 15
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<\0\fIfileName\fR
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The file named by \fIfileName\fR is opened and used as the standard
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input for the first command in the pipeline.
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.TP 15
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<@\0\fIfileId\fR
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.VS
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\fIFileId\fR must be the identifier for an open file, such as the return
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value from a previous call to \fBopen\fR.
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It is used as the standard input for the first command in the pipeline.
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\fIFileId\fR must have been opened for reading.
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.VE
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.TP 15
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<<\0\fIvalue\fR
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\fIValue\fR is passed to the first command as its standard input.
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.TP 15
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>\0\fIfileName\fR
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Standard output from the last command is redirected to the file named
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\fIfileName\fR, overwriting its previous contents.
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.TP 15
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2>\0\fIfileName\fR
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.VS
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Standard error from all commands in the pipeline is redirected to the
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file named \fIfileName\fR, overwriting its previous contents.
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.TP 15
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>&\0\fIfileName\fR
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Both standard output from the last command and standard error from all
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commands are redirected to the file named \fIfileName\fR, overwriting
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its previous contents.
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.VE
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.TP 15
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>>\0\fIfileName\fR
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Standard output from the last command is
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redirected to the file named \fIfileName\fR, appending to it rather
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than overwriting it.
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.TP 15
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2>>\0\fIfileName\fR
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.VS
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Standard error from all commands in the pipeline is
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redirected to the file named \fIfileName\fR, appending to it rather
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than overwriting it.
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.TP 15
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>>&\0\fIfileName\fR
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Both standard output from the last command and standard error from
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all commands are redirected to the file named \fIfileName\fR,
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appending to it rather than overwriting it.
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.TP 15
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>@\0\fIfileId\fR
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\fIFileId\fR must be the identifier for an open file, such as the return
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value from a previous call to \fBopen\fR.
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Standard output from the last command is redirected to \fIfileId\fR's
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file, which must have been opened for writing.
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.TP 15
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2>@\0\fIfileId\fR
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\fIFileId\fR must be the identifier for an open file, such as the return
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value from a previous call to \fBopen\fR.
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Standard error from all commands in the pipeline is
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redirected to \fIfileId\fR's file.
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The file must have been opened for writing.
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.TP 15
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>&@\0\fIfileId\fR
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\fIFileId\fR must be the identifier for an open file, such as the return
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value from a previous call to \fBopen\fR.
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Both standard output from the last command and standard error from
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all commands are redirected to \fIfileId\fR's file.
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The file must have been opened for writing.
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.VE
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.PP
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If standard output has not been redirected then the \fBexec\fR
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command returns the standard output from the last command
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in the pipeline.
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If any of the commands in the pipeline exit abnormally or
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are killed or suspended, then \fBexec\fR will return an error
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and the error message will include the pipeline's output followed by
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error messages describing the abnormal terminations; the
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\fBerrorCode\fR variable will contain additional information
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about the last abnormal termination encountered.
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If any of the commands writes to its standard error file and that
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standard error isn't redirected,
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then \fBexec\fR will return an error; the error message
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will include the pipeline's standard output, followed by messages
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about abnormal terminations (if any), followed by the standard error
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output.
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.PP
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If the last character of the result or error message
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is a newline then that character is normally deleted
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from the result or error message.
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This is consistent with other Tcl return values, which don't
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normally end with newlines.
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.VS
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However, if \fB\-keepnewline\fR is specified then the trailing
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newline is retained.
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.VE
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.PP
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If standard input isn't redirected with ``<'' or ``<<''
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or ``<@'' then the standard input for the first command in the
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pipeline is taken from the application's current standard input.
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.PP
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If the last \fIarg\fR is ``&'' then the pipeline will be
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executed in background.
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.VS
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In this case the \fBexec\fR command will return a list whose
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elements are the process identifiers for all of the subprocesses
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in the pipeline.
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.VE
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The standard output from the last command in the pipeline will
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go to the application's standard output if it hasn't been
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redirected, and error output from all of
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the commands in the pipeline will go to the application's
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standard error file unless redirected.
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.PP
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The first word in each command is taken as the command name;
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tilde-substitution is performed on it, and if the result contains
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no slashes then the directories
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in the PATH environment variable are searched for
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an executable by the given name.
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If the name contains a slash then it must refer to an executable
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reachable from the current directory.
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No ``glob'' expansion or other shell-like substitutions
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are performed on the arguments to commands.
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.SH KEYWORDS
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execute, pipeline, redirection, subprocess
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