$ perl -e 'my $1;'
Can't use global $1 in "my" at -e line 1, near "my $1"
Execution of -e aborted due to compilation errors.
$ perl -e 'my $1 = 42;'
Can't use global $1 in "my" at -e line 1, near "my $1 "
Execution of -e aborted due to compilation errors.

##</code><code>##

use diagnostics;