Regular Expressions

^$ -> empty line
[a-z3-7] -> small alpha or a number between 3 and 7
a*b -> b, ab, aab
a?b -> b, ab
a+b -> ab, aab
^a$b -> line starting with letter a and ending with letter b
[^a-f] -> except for a to f
ab. > ab followed by any character except for new line
35\{4\} -> 35555
re(ab)d -> read, rebd
\ -> exact word "sin"
a\$ => a$
a$ => line ending with a
[:upper:] [:lower:] [:alpha:] [:print:] [:digit:] [:cntrl:][:blank:][:space:][:xdigit:]