http://www.purl.org/tcl/home/man/tcl8.4/TclCmd/scan.htm
display and numeric format for ASCII characters. display and numeric format for ASCII characters. Scan provides the usual answer:
foreach character {a A b B c} { scan $character %c numeric puts "ASCII character '$numeric' displays as '$character'." } ASCII character '97' displays as 'a'. ASCII character '65' displays as 'A'. ASCII character '98' displays as 'b'. ASCII character '66' displays as 'B'. ASCII character '99' displays as 'c'.
Tcl syntax help - Arts and crafts of Tcl-Tk programming - Category Command