See `perldoc -f eval`

If there is a syntax error or runtime error, or a die() statement is executed, an undefined value is returned by eval(), and $@ is set to the error message. If there was no error, $@ is guaranteed to be a null string. Beware that using eval() neither silences perl from printing warnings to STDERR, nor does it stuff the text of warning messages into $@. To do either of those, you have to use the $SIG{__WARN__} facility. See warn and the perlvar manpage.

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