$ perl -Mwarnings -E 'say "123test" + 5'
Argument "123test" isn't numeric in addition (+) at -e line 1.
128
$ perl -Mwarnings -E 'say "0 but true" + 5'
5
$ perl -Mwarnings -E 'say "0 but true" == 0'
1
$ perl -Mwarnings -E 'say "123test" == 123'
Argument "123test" isn't numeric in numeric eq (==) at -e line 1.
1