exec(n) Tcl (7.0) exec(n)
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NAME
exec - Invoke subprocess(es)
SYNOPSIS
exec ?switches? arg ?arg ...?
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DESCRIPTION
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 arg becomes one
word of a command, and each distinct command becomes a
subprocess.
If the initial arguments to exec start with - then they are |
treated as command-line switches and are not part of the |
pipeline specification. The following switches are |
currently supported: |
-keepnewline ||
Retains a trailing newline in the pipeline's |
output. Normally a trailing newline will be |
deleted. |
-- ||
Marks the end of switches. The argument |
following this one will be treated as the first |
arg even if it starts with a -.
If an arg (or pair of arg's) has one of the forms described
below then it is used by exec 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 ``< |
fileName'' fileName may either be in a separate argument |
from ``<'' or in the same argument with no intervening space |
(i.e. ``<fileName'').
| Separates distinct commands in the pipeline.
The standard output of the preceding command
will be piped into the standard input of the
next command.
|& 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 >&.
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exec(n) Tcl (7.0) exec(n)
< fileName The file named by fileName is opened and used
as the standard input for the first command
in the pipeline.
<@ fileId FileId must be the identifier for an open |
file, such as the return value from a |
previous call to open. It is used as the |
standard input for the first command in the |
pipeline. FileId must have been opened for |
reading.
<< value Value is passed to the first command as its
standard input.
> fileName Standard output from the last command is
redirected to the file named fileName,
overwriting its previous contents.
2> fileName Standard error from all commands in the |
pipeline is redirected to the file named |
fileName, overwriting its previous contents. |
>& fileName ||
Both standard output from the last command |
and standard error from all commands are |
redirected to the file named fileName, |
overwriting its previous contents.
>> fileName Standard output from the last command is
redirected to the file named fileName,
appending to it rather than overwriting it.
2>> fileName Standard error from all commands in the |
pipeline is redirected to the file named |
fileName, appending to it rather than |
overwriting it. |
>>& fileName ||
Both standard output from the last command |
and standard error from all commands are |
redirected to the file named fileName, |
appending to it rather than overwriting it. |
>@ fileId ||
FileId must be the identifier for an open |
file, such as the return value from a |
previous call to open. Standard output from |
the last command is redirected to fileId's |
file, which must have been opened for |
writing. |
2>@ fileId ||
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exec(n) Tcl (7.0) exec(n)
FileId must be the identifier for an open |
file, such as the return value from a |
previous call to open. Standard error from |
all commands in the pipeline is redirected to |
fileId's file. The file must have been |
opened for writing. |
>&@ fileId ||
FileId must be the identifier for an open |
file, such as the return value from a |
previous call to open. Both standard output |
from the last command and standard error from |
all commands are redirected to fileId's file. |
The file must have been opened for writing.
If standard output has not been redirected then the exec
command returns the standard output from the last command in
the pipeline. If any of the commands in the pipeline exit
abnormally or are killed or suspended, then exec will return
an error and the error message will include the pipeline's
output followed by error messages describing the abnormal
terminations; the errorCode variable 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 isn't redirected, then exec 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.
If the last character of the result or error message is a
newline then that character is normally deleted from the
result or error message. This is consistent with other Tcl
return values, which don't normally end with newlines. |
However, if -keepnewline is specified then the trailing |
newline is retained.
If standard input isn't redirected with ``<'' or ``<<'' or
``<@'' then the standard input for the first command in the
pipeline is taken from the application's current standard
input.
If the last arg is ``&'' then the pipeline will be executed
in background. In this case the exec command will return a |
list whose elements are the process identifiers for all of |
the subprocesses in the pipeline. The standard output from
the last command in the pipeline will go to the
application's standard output if it hasn't been redirected,
and error output from all of the commands in the pipeline
will go to the application's standard error file unless
redirected.
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exec(n) Tcl (7.0) exec(n)
The first word in each command is taken as the command name;
tilde-substitution is performed on it, and if the result
contains no slashes then the directories in the PATH
environment variable are searched for an executable by the
given name. If the name contains a slash then it must refer
to an executable reachable from the current directory. No
``glob'' expansion or other shell-like substitutions are
performed on the arguments to commands.
KEYWORDS
execute, pipeline, redirection, subprocess
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