Gawk/Regexp-Patterns

From Get docs

7.1.1 Regular Expressions as Patterns

Regular expressions are one of the first kinds of patterns presented in this book. This kind of pattern is simply a regexp constant in the pattern part of a rule. Its meaning is ‘$0 ~ /pattern/’. The pattern matches when the input record matches the regexp. For example:

/foo|bar|baz/  { buzzwords++ }
END            { print buzzwords, "buzzwords seen" }