In order to give you a quick reference to the different patterns and what they will match, here's a comprehensive table of all we've covered. Column one contains example expressions, and column two contains what that expression will match.
the string "foo"
"foo" at the start of a line
"foo" at the end of a line
"foo" when it is alone on a line
"Foo" or "foo"
a, b, or c
d, e, f, g, h, etc - everything that is not a, b, or c (^ is "not" inside sets)
any uppercase letter
any lowercase letter
any letter of number
one or more uppercase letters
zero or more uppercase letters
zero or one uppercase letters
3 uppercase letters
a minimum of 3 uppercase letters
1-3 uppercase letters
any non-numeric character
any symbol (not a number or a letter)
F, Fo, Foo, Fooo, Foooo, etc
Fo, Foo, Fooo, Foooo, etc
any character except \n (new line)
a word boundary. E.g. te\b matches the "te" in "late", but not the "te" in "tell".
a non-word boundary. "te\B" matches the "te" in "tell" but not the "te" in "late".