cd man page
cd — Change working directory
Change the current working directory to dirName, or to the home directory (as specified in the HOME environment variable) if dirName is not given. Returns an empty string. Note that the current working directory is a per-process resource; the cd command changes the working directory for all interpreters and (in a threaded environment) all threads.
Change to the home directory of the user fred:
Change to the directory lib that is a sibling directory of the current one:
filename(n), glob(n), pwd(n)
pwd(n), source(n), Tcl_FSRegister(3).