exec(3Tcl) exec(3Tcl)
exec - Invoke subprocess(es)
exec ?switches? arg ?arg ...?
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 >&.
< 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.
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exec(3Tcl) exec(3Tcl)
> 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 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.
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exec(3Tcl) exec(3Tcl)
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.
The first word in each command is taken as the command name; tildesubstitution
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.
execute, pipeline, redirection, subprocess
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