special commands meaning matches doesn't match . any character almost everything end of line "\n" A* zero, one or more A "", "A" or "AAAA" "B", almost everything else .* something in between "asghas" matches everything A.*B A and B and something in between "Alligator Berni" or "AB" "AC" x+ one or more "x" "x", "xx" or "xxxx" "" or "alpha" \d a digit "1" or "6" "xyz" \s whitespace " " or "\t" "abc" [ABD] one of the characters between brackets "A", "B" or "D" "C" [a-z]+ one or more lower case characters "alpha" or "butter" "ALPHA" (alpha|beta|gamma) one of the words "alpha", "beta" or "gamma" "alpha" "berta" ^ beginning of line     ^A   a line starting with "A" a line starting with any other character $ end of line     )$   right parenthesis at the end of line any other character at the end of line ^.{10}$   a line exactly 10 characters long any other line length

RegularExpressions can become arbitrarily complex. There are tutorials and books on this topic. This is just to give you a taste of it.