The simplest approach to execute the input text is eval.

Depending if it's just a personal play tool or an application for other users you should consider limiting what input is executed!

E.g. Grandfather showed you an approach to limit input to methods of a special class w/o eval, which is quite safe!

Example: Just taking the synopsis-code from term-readline already does most of the trick. Additionally limiting to package 'allowed_subs" is a (weaker) protection against misuse.

use Term::ReadLine;
my $term = Term::ReadLine->new('Simple Perl calc');
my $prompt = "Enter code: ";
my $OUT = $term->OUT || \*STDOUT;
while ( defined ($_ = $term->readline($prompt)) ) {
  my $res = eval("package allowed_subs; $_");
  warn $@ if $@;
  print $OUT $res, "\n" unless $@;
  $term->addhistory($_) if /\S/;
}
  
package allowed_subs;
 
sub ab {
  `xmessage "@_"`       # Pop-Up input  (linux only)
}
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