9.04 before I do anything

root@cow:/home/peter# dpkg -l|grep tcl
ii  tcl                                        8.4.16-2                           The Tool Command Language (default version)
ii  tcl8.4                                     8.4.19-2                           Tcl (the Tool Command Language) v8.4 - run-t
root@cow:/home/peter#

maybe this is installed as a dep for git,since gitk require this.

/usr/bin/tclsh8.4
/usr/lib
/usr/lib/libtcl8.4.so.0
root@cow:/home/peter# tclsh8.4
%

the helloworld

root@cow:/home/peter# tclsh dd.tcl
peter
root@cow:/home/peter# which  tclxh
root@cow:/home/peter# which  tclsh
/usr/bin/tclsh
root@cow:/home/peter# file /usr/bin/tclsh
/usr/bin/tclsh: symbolic link to `/etc/alternatives/tclsh'
root@cow:/home/peter# file /etc/alternatives/tclsh
/etc/alternatives/tclsh: symbolic link to `/usr/bin/tclsh-default'
root@cow:/home/peter# file /usr/bin/tclsh-default
/usr/bin/tclsh-default: symbolic link to `tclsh8.4'
root@cow:/home/peter#

so I had this run as tt.tcl

puts stdout {peter}
set var 5
set b $var
puts stdout $b

string length foobar

Doc

http://www.beedub.com/book/

Tcl Introduction