sub make_sub {
  my ( $sub_name, $code ) = @_ ;
  local $@;
  eval "sub $sub_name { $code }" ;
  die "make_sub $sub_name: $@\n" if $@;
}

make_sub( say_hello => 'print "Hello @_\n"' );
say_hello( 'World' );
__END__
Hello World

##</code><code>##

package MyFunctions;
# save this as MyFunctions.pm

sub say_hello {
  shift ;             # discard class name: perldoc perlboot
  print "Hello @_\n"
}

sub list_dir {
  shift ;             # discard class name

  require Cwd;
  my $owd = Cwd::cwd();
  my $dir = shift;
  chdir $dir or die "chdir $dir: $!\n";

  print $_ . "\n" while <*> ;
   
  chdir $owd;
}


1;

##</code><code>##

#!/usr/bin/perl
# save this as program.pl

use strict;
use warnings;
use MyFunctions;

print "action> " ;
chomp( my $action = <STDIN> );
print "args> ";
chomp( my $arg = <STDIN> );

MyFunctions->$action( $arg );

##</code><code>##

$ perl program.pl
action> list_dir
args> /tmp
foo
bar
baz