http://purl.org/tcl/home/man/tcl8.4/TclCmd/cd.htm
A frequently made mistake FMM [L1 ] that programmers make is to attempt to exec the cd command. cd stands for change directory. This sets a kernel specific piece of information regarding what files within a filesystem the application will see if they use relative pathnames (that is to say, pathnames either beginning with ./ , ../ , or without any leading directory indicatory).
This kernel value is a unique value per process - changing it in one process won't change it in other existing processes.
Stacking cd: The following overloaded version keeps a stack of visited directories (implicit "pushd"). The "popd" functionality fires if called as "cd -":
if {[info command tcl::cd]==""} {rename cd tcl::cd}
proc cd {{dir ""}} {
global cd_stack
if {$dir=="-"} {
set dir [lindex $cd_stack end]
set cd_stack [lrange $cd_stack 0 end-1]
} else {
if {$dir==""} {set dir $::env(HOME)}
lappend cd_stack [pwd]
}
tcl::cd $dir
} ;# RSTcl syntax help - Arts and crafts of Tcl-Tk programming - Category Command