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There's a charming example in the Perl Cookbook that ties global $_ so you get diagnostics when $_ is used globally (modified to be able to carp instead of croak if you want):
# croak on global underscore usage: # no Underscore; # carp on global underscore usage: # no Underscore 'carp'; package Underscore; use Carp (); my $complain = \&Carp::croak; sub TIESCALAR { bless \(my $dummy) => shift } sub FETCH { $complain->("read access to \$_ forbidden") } sub STORE { $complain->("write access to \$_ forbidden") } sub unimport { tie($_, __PACKAGE__); $complain = \&Carp::carp if $_[1] eq 'carp'; } sub import { untie $_ } tie($_, __PACKAGE__) unless tied $_; 1;
And you save it as Underscore.pm and use it by just adding a no Underscore; or no Underscore 'croak'; . Or you can do it at the command line, of course, using perl -M-Underscore myprog.pl or perl -M-Underscore=carp myprog.pl

In reply to Detecting global $_ usage by bikeNomad
in thread When is $_ local and when is it not? by iakobski

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