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.]]

See also [Concepts of Architectural Design for Tcl Applications] and [Inventory of IPC methods].

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It's quick work in Tcl to code a
    proc perl_interpret script {
        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";
     }]

[Phil Ehrens] offers a slightly more elaborate version:
      proc perl { args } {
           set perl_opts -e
           foreach arg $args {
              # pick off things that look like options
              # to pass to perl
              if { [ regexp {^-+\S+$} $arg ] } {
                 set perl_opts [ concat $arg $perl_opts ]
              } else {
                # and the rest is the code and the file args 
                lappend perl_code $arg
              }
           }
           # this is the debugging code ;^)
           puts stderr "perl $perl_opts $perl_code"
           catch { eval exec perl $perl_opts $perl_code } result
           return $result
      }
An example usage of this is
      perl "print \"foo!\n\"; print \"bar\""




















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