I use this as a commandline calculator, but it can easily fit in any interactive program.
CAUTION: s///'ing does NOT make this safe. 123x123x123x123 will still let your box have a hard time.
#!/usr/local/bin/perl

$a = "@ARGV";

$a =~ s/[^*.+\-0-9&|\)\(x\/\^]//g;
# Unnecessary escapes are for my syntax hilighter.
# Please don't nag about them :)
$a =~ s/\*\*/^/g;
$a =~ s/([*+.\/x-])\1*/$1/g;
$a =~ s/\^/**/g;
eval("print($a)");
print "\n";

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In reply to Simple calculator by Juerd

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