print eval('5+2-1');

但这不安全：

print eval('print "You are hacked"');

您需要在评估之前检查字符串.
您也可以使用来自cpan的Math::Expression模块或许多其他模块：

#!/usr/bin/perl

use strict;
use warnings;
use Math::Expression;

my $env = Math::Expression->new;

my $res = $env->Parse( '5+2-1' );

# my $res = $env->Parse( 'print you are hacked' );  # no math expression here

print $env->Eval( $res );