=over =item $PREMATCH =item $` X<$`> X<$PREMATCH> X<${^PREMATCH}> The string preceding whatever was matched by the last successful pattern match, not counting any matches hidden within a BLOCK or C 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 L. Starting with Perl 5.10, you can use the C

match flag and the C<${^PREMATCH}> variable to do the same thing for particular match operations. This variable is read-only and dynamically-scoped. Mnemonic: C<`> often precedes a quoted string. =back