```{index} single: readonly (Scalar::Util) ``` ```{index} single: Scalar::Util::readonly ``` # readonly `readonly($var)` - returns true if `$var` is read-only. The true value is not `1`. Exactly as in perl5, it is the raw internal flag word, so a read-only scalar yields a number such as 134283264. Test it for truth; never compare it against `1`. Takes exactly one argument. sub foo { readonly($_[0]) } $ro = foo($bar); # false $ro = foo(0); # true