github.com/benhoyt/goawk@v1.8.1/testdata/t.re1a (about)

     1  BEGIN { r1 = "[a-cg-j1-3]"
     2  	r2 = "[^aeiou]"
     3  }
     4  
     5  $0 ~ r1	{ print $0 " matches /[a-cg-j1-3]/" }
     6  $0 ~ r2	{ print $0 " matches /[^aeiou]/" }