File: gawk.info,  Node: Regexp Constants,  Prev: Nondecimal-numbers,  Up: Constants

6.1.1.3 Regular Expression Constants
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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).