He used positive look ahead assertions to test if the two patterns 'fred' and 'bill' were both in the string being matched. Essentially, it's the same thing as saying /fred/ && /bill/.

Also, it's anchored to increase performance, since it if doesn't match at the beginning of the string, it won't match at all.

perldoc - perlre: Just search for "Look-Around Assertions"

In reply to Re^3: Regex match at the beginning or end of string by wind
in thread Regex match at the beginning or end of string by cyber-guard

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