Arguments to your Expect script are in the global array $argc. Grabbing an old Expect script, here is a sample of how you can manually process command-line arguments:

set i 0
while {$i < $argc} {
  if ![string compare "-m" [lindex $argv $i]] {
    incr i
    if $i==$argc {
      send_user "-m specified without machine, FAILING"
      exit -3
    }
    set machine [lindex $argv $i]
  } elseif ![string compare "-n" [lindex $argv $i]] {
    incr i
    if $i==$argc {
      send_user "-n specified without name, FAILING"
      exit -3
    }
    set name [lindex $argv $i]
  } elseif ![string compare "-p" [lindex $argv $i]] {
    incr i
    if $i==$argc {
      send_user "-p specified without password, FAILING"
      exit -3
    }
    set password [lindex $argv $i]
  } elseif ![string compare "-c" [lindex $argv $i]] {
    incr i
    if $i==$argc {
      send_user "-c specified without argument, FAILING"
      exit -3
    }
    set cmd [lindex $argv $i]
  }
  incr i
}
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Now Perl can pass things on the command line. I don't know enough TCL to know if there is a cleaner way to do this processing (I would *hope* that there is). But it works.

Incidentally I would suggest that before hand-rolling a lot of Expect scripts that you look to CPAN for modules to drive the same things. For instance try Net::Telnet or failing that, Expect. Then you don't need to mix languages and error handling will probably be a bit easier as a result...