perl -e "use strict; my $1='foo'; if ($foo=~/(f)/){print $1;}"
Can't use global $1 in "my" at -e line 1, near "my $1"
Global symbol "$foo" requires explicit package name at -e line 1.
Execution of -e aborted due to compilation errors.

##</code><code>##

perl -e "my $1='foo'; if ($1=~/(f)/){print $1;}"
Can't use global $1 in "my" at -e line 1, near "my $1"
Execution of -e aborted due to compilation errors.