Regular Expression Cheatsheet

\d    numeric character [0-9]
\D    NOT a numeric character [^0-9]
\w    “word” character [a-zA-Z0-9_]
\W    NOT a “word” character [^a-zA-Z0-9_]
\s    whitespace character [\f\n\r\t\v]
\S    NOT a whitespace character [^\f\n\r\t\v]
.    Any character except a line break [^\n]
()    group
?    zero or one
*    zero to many
+    one to many
{x}    match x times
{x,y}    match x to y times

Reference: Regular Expressions: Not as Tricky as They May Seem