There are several ways to execute [Perl] programs from Tcl applications.
Most succinct is simply to apply Tcl's powerful [exec]
in a command such as
    exec my_program.pl

[[Explain [open], and other IPC, more generally.]]

----
It's quick work in Tcl to code a
    proc perl_interpret scripte {
        return [exec perl << [uplevel [list subst -novariables -noback $script]]]
    }
which allows one to write
    set a 13
    set b 79

     puts [perl_interpret {
        $result = [set a] + [set b];
       print "The sum is ", $result, ".\n";
     }]




[Tclperl] is quite nice.  So is the [Perl widget], although in a much
different way.