避免“在数值eq(==)中”的最佳方法是警告。

#!/usr/bin/env perl
use warnings;
use 5.12.2;

my $c = 'f'; # could be a number too

if ( $c eq 'd' || $c == 9 ) {
    say "Hello, world!";
} 
#!/usr/bin/env perl
use warnings;
use 5.12.2;