^TI^'
^TITW^history 
^TITW^substitute 
^TIS^old 
^TIS^new 
^TIS^eventSpec 
^TI^' Command
^P^
Retrieves the command given by the optional argument 
^S^eventSpec
 (-1 by default), replaces any occurrences of 
^S^old
 with 
^S^new
 in the command (only simple character equality is supported; 
no wild cards), executes the resulting command, and returns 
the result of that execution. 
This command results in history revision: see the Tcl man page for 
details.
