#!/usr/bin/perl

use 5.010_000;  # re features

use warnings;
use strict;

our @stack;
our $result;

my %unary_ops = (
    chs  => sub { $_[0] = -$_[0] },
    abs  => sub { $_[0] = abs $_[0] },
    sqr  => sub { $_[0] *= $_[0] },
    sqrt => sub { $_[0] = sqrt $_[0] },
    sin  => sub { $_[0] = sin $_[0] },
    cos  => sub { $_[0] = cos $_[0] },
    tan  => sub { $_[0] = sin $_[0] / cos $_[0] },
);

my %binary_ops = (
    '+' => sub { $_[0] += $_[1] },
    '-' => sub { $_[0] -= $_[1] },
    '/' => sub { $_[0] /= $_[1] },
    '*' => sub { $_[0] *= $_[1] },
    '^'  => sub { $_[0]**= $_[1] },
);

my $RPN = qr{
   ...
};

my %input = (
   ...
);

foreach my $line ( keys %input ) {
    local $result;
    my ($expression) = $line =~ /($RPN)/;
    ...
}