http://www.purl.org/tcl/home/man/tcl8.4/TclCmd/tclvars.htm
$::errorCode contains error information in various cases (see the man page above); one of these cases is the exit status of the last exec or open "|..."/close pair that received an error.
See also tclvars, error, and return.
Anyone have good programming practices for using this?
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