The string preceding whatever was matched by the last successful pattern match, not counting any matches hidden within a BLOCK or eval enclosed by the current BLOCK.
The use of this variable anywhere in a program imposes a considerable performance penalty on all regular expression matches. To avoid this penalty, you can extract the same substring by using "@-". Starting with Perl 5.10, you can use the </p> match flag and the ${^PREMATCH} variable to do the same thing for particular match operations.
This variable is read-only and dynamically-scoped.
Mnemonic: ` often precedes a quoted string.