http://purl.org/tcl/home/man/tcl8.4/TclCmd/close.htm

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[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...
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[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}

See also [exec]
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See also [channel].
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