github.com/benhoyt/goawk@v1.8.1/testdata/t.re3 (about)

     1  {	r1 = $1
     2  	r2 = $1 ":"
     3  }
     4  
     5  length(r1) && $0 ~ r1	{ print $0 " matches " r1 }
     6  length(r1) && $0 ~ r2	{ print $0 " matches " r2 }