The Perl error from the last eval operator, i.e. the last exception that was caught. For eval BLOCK, this is either a runtime error message or the string or reference die was called with. The eval STRING form also catches syntax errors and other compile time exceptions.
If no error occurs, eval sets $@ to the empty string.
Warning messages are not collected in this variable. You can, however, set up a routine to process warnings by setting $SIG{__WARN__} as described in "%SIG".
Mnemonic: Where was the error "at"?