When [tclsh] is invoked interactively, it normally prompts for each
command with '''% '''.  You can change the prompt by setting the Tcl global
variables ''tcl_prompt1'' and [tcl_prompt2].  If variable '''tcl_prompt1'''
exists, then it must consist of a Tcl script to output a prompt;
instead of outputting the '''% ''' prompt, tclsh will evaluate the script in
tcl_prompt1.

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