The value of this variable can be set to control how much tracing information is displayed during bytecode execution. By default, tcl_traceExec is zero and no information is displayed. Setting tcl_traceExec to 1 generates a one-line trace in stdout on each call to a Tcl procedure. Setting it to 2 generates a line of output whenever any Tcl command is invoked that contains the name of the command and its arguments. Setting it to 3 produces a detailed trace showing the result of executing each bytecode instruction. Note that when tcl_traceExec is 2 or 3, commands such as set and incr that have been entirely replaced by a sequence of bytecode instructions are not shown. Setting this variable is useful in tracking down suspected problems with the bytecode compiler and interpreter.

This variable and functionality only exist if TCL_COMPILE_DEBUG was defined during Tcl's compilation. (from the "tclvars" manpage)

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