Turn the problem around. If you look at it as having Perl around command interpreter snippets, the problem becomes different:

#!/usr/bin/perl -w
use strict;

use vars qw($last_status);

sub run_external {
    my $cmd = shift;
    print "Running [$cmd]";
    $last_status = system($cmd);
    $last_sys_error = $?;
    return $last_status
};

run_external(<<COMMAND);
    command1 param1=value1 param2=value2
COMMAND

for my $machine (@machines) {
    run_external(<<COMMAND);
    command1 machine=$machine param1=value1 param2=value2
COMMAND

    if ($last_status) {
        run_external(<<COMMAND);
              debugging_command machine=$machine debug_param1=debug_va
+lue1
COMMAND
    };
};
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Of course, this requires you to start all your new/complex files with Perl and your simple files with the other interpreter/the shell. I would write a wrapper that checks (say) the file extension or whatnot to launch the correct interpreter for the program.