pid(3tcl) Tcl Built-In Commands pid(3tcl)__________________________________________________________________________________________________________________________________________________NAME
pid - Retrieve process identifiers
SYNOPSIS
pid ?fileId?
_________________________________________________________________DESCRIPTION
If the fileId argument is given then it should normally refer to a process pipeline created with the open command. In this case the pid
command will return a list whose elements are the process identifiers of all the processes in the pipeline, in order. The list will be
empty if fileId refers to an open file that is not a process pipeline. If no fileId argument is given then pid returns the process identi-
fier of the current process. All process identifiers are returned as decimal strings.
EXAMPLE
Print process information about the processes in a pipeline using the SysV ps program before reading the output of that pipeline:
set pipeline [open "| zcat somefile.gz | grep foobar | sort -u"]
# Print process information
exec ps -fp [pid $pipeline] >@stdout
# Print a separator and then the output of the pipeline
puts [string repeat - 70]
puts [read $pipeline]
close $pipeline
SEE ALSO exec(3tcl), open(3tcl)KEYWORDS
file, pipeline, process identifier
Tcl 7.0 pid(3tcl)
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close(3tcl) Tcl Built-In Commands close(3tcl)__________________________________________________________________________________________________________________________________________________NAME
close - Close an open channel
SYNOPSIS
close channelId
_________________________________________________________________DESCRIPTION
Closes the channel given by channelId.
ChannelId must be an identifier for an open channel such as a Tcl standard channel (stdin, stdout, or stderr), the return value from an
invocation of open or socket, or the result of a channel creation command provided by a Tcl extension.
All buffered output is flushed to the channel's output device, any buffered input is discarded, the underlying file or device is closed,
and channelId becomes unavailable for use.
If the channel is blocking, the command does not return until all output is flushed. If the channel is nonblocking and there is unflushed
output, the channel remains open and the command returns immediately; output will be flushed in the background and the channel will be
closed when all the flushing is complete.
If channelId is a blocking channel for a command pipeline then close waits for the child processes to complete.
If the channel is shared between interpreters, then close makes channelId unavailable in the invoking interpreter but has no other effect
until all of the sharing interpreters have closed the channel. When the last interpreter in which the channel is registered invokes close,
the cleanup actions described above occur. See the interp command for a description of channel sharing.
Channels are automatically closed when an interpreter is destroyed and when the process exits. Channels are switched to blocking mode, to
ensure that all output is correctly flushed before the process exits.
The command returns an empty string, and may generate an error if an error occurs while flushing output. If a command in a command pipe-
line created with open returns an error, close generates an error (similar to the exec command.)
EXAMPLE
This illustrates how you can use Tcl to ensure that files get closed even when errors happen by combining catch, close and return:
proc withOpenFile {filename channelVar script} {
upvar 1 $channelVar chan
set chan [open $filename]
catch {
uplevel 1 $script
} result options
close $chan
return -options $options $result
}
SEE ALSO file(3tcl), open(3tcl), socket(3tcl), eof(3tcl), Tcl_StandardChannels(3tcl)KEYWORDS
blocking, channel, close, nonblocking
Tcl 7.5 close(3tcl)