BRE's need to escape () {} and can use \n as the nth backreference
^ first character on line
$ last character on line
. matches any single character
* matches preceding element 0 or more times
{m/n} matches preceding element at least m and no more than n times
? matches preceding element 0 or 1 times (ERE only)
+ matches preceding element 1 or more times (ERE only)
| or operator (ERE only)
[ ] matches any single character in brackets (a-z, A-Z, 0-9... allowed for character ranges)
[^ ] matches any single character not in brackets
( ) sub-expression
Character classes:
[:alnum:] alphanumeric [A-Za-z0-9]
[:alpha:] alphabetic [A-Za-z]
[:blank:] space and tab
[:cntrl:] control characters
[:digit:] numbers [0-9]
[:graph:] visible characters
[:lower:] lowercase letters
[:upper:] uppercase letters
[:print:] visible and space characters
[:punct:] punctuation characters []!"#$%^&'()*+,./:;=<>?\@`{}|~-_
[:space:] whitespace characters
[:xdigit:] hexadecimal digits [A-Fa-f0-9]
