A simple shell can be done with perls eval. You only need to create subroutines that do what you want to do. The big plus is you get the power of perl for free with that

a really trivial example to show what I mean:

#!/usr/bin/perl
use warnings;
use strict;

sub coordinate {
  print '<'.join("><",@_),">\n";
}

while (<>) {
  no strict;
  eval $_;
}
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Now you can do this:

> ./t7.pl
coordinate 4
<4>
coordinate "test","west","best"
<test><west><best>
$n=4      
coordinate $n
<4>
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