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

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$::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].


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Anyone have good programming practices for using this?


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