Info Catalog
gawk: Nondecimal-numbers
gawk: Constants
6.1.1.3 Regular Expression Constants .................................... A "regexp constant" is a regular expression description enclosed in slashes, such as '/^beginning and end$/'. Most regexps used in 'awk' programs are constant, but the '~' and '!~' matching operators can also match computed or dynamic regexps (which are typically just ordinary strings or variables that contain a regexp, but could be more complex expressions).