close - Close an open channel
close channelId ?r(ead)|w(rite)?'
TCL core command
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.
If r (or read) is present and channelId was opened bidirectionally, then the channel will be “half-closed” so that it becomes only possible to write to it. Conversely with w (or write) which closes the reader side of a bidirectional channel. This is particularly useful with a pipe or socket.
http://www.tcl.tk/man/tcl8.5/TclCmd/close.htm
file, open, socket, eof, channel, exec, stderr
set fh [open output.txt r] set data [read $fh] close $fh
LV What are the ramifications if you don't close a file in Tcl? Any? I assume a memory leak in long running daemon type apps...
glennj: When working with pipes (i.e. [set pipe [open "| some command"]]]), and the pipe is blocking (i.e. [fconfigure $pipe -blocking yes] which is the default), then [close $pipe] throws an error if the command exited with non-zero status or if the command sent any output to stderr.
example:
set command {sh -c {echo "to stdout"; echo >&2 "to stderr"; exit 42}}
set pipe [open "| $command"]
set standard_output [read -nonewline $pipe]
set exit_status 0
if {[catch {close $pipe} standard_error] != 0} {
global errorCode
if {"CHILDSTATUS" == [lindex $errorCode 0]} {
set exit_status [lindex $errorCode 2]
}
}
puts "exit status is $exit_status"
puts "captured standard output: {$standard_output}"
puts "captured standard error: {$standard_error}"Output is:
exit status is 42
captured standard output: {to stdout}
captured standard error: {to stderr}AMG: TIP #332 "Half-Close for Bidirectional Channels" [L1 ] adds an optional argument to specify which direction of the channel to close, like the shutdown(2) system call [L2 ].
close channel ?read|write?