You can have the power of the tools of tomorrow today already:

export PERL5OPT=-Mstrict -w
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will make your Perl run automatically with use strict; use warnings; enabled and will even use the use warnings; equivalent if the warnings pragma isn't in your Perl already (see perlrun). For maximum effect, put that line into /etc/profile or wherever your users' environment gets set up.

~ $ PERL5OPT="-Mstrict -w" perl -e 'print $y'
Global symbol "$y" requires explicit package name at -e line 1.
Execution of -e aborted due to compilation errors.
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If you want to disable the effect, use no strict; or no warnings; in your scripts or oneliners respectively.