Regular Expression Summary

### Regular Expression Help

The following match as stated:

. | any single character
$ | end of a line
\< | start of a word
\b | either edge of a word
[asd] | a, s or d
[^a-zA-Z] | Anything except a letter (the ^ negates)
^ | beginning of a line
\> | end of a word
\B | empty string not at the edge of a word
[a-d 0-9] | abcd0123456789 or space

Repetition Operators:

? | The preceding item will be matched zero or one times
* | The preceding item will be matched zero or more times
+ | The preceding item will be matched one or more times
{n} | The preceding item will be matched exactly n times
{n,} | The preceding item will be matched n or more times
{n,m} | The preceding item will be matched from n to m times

Shortcuts:
[:alpha:] [:lower:] [:upper:] [:digit:] [:alnum:] [:punct:] [:blank:] [:cntrl:] [:graph:] [:print:] [:space:] [:xdigit:]
[:blank:] means space or tab. [:space:] means space tab CR FF NL or VT
[:print:] means [:alnum:], [:punct:] or [:space:]
[:xdigit:] means a hexadecimal digit, i.e. [0-9A-Fa-f]
Note that these shortcuts still need to be in brackets. Yes, really! e.g. [[:punct:]e] matches punctuation or 'e'
\w is a synonym for [[:alnum:]] \W is a synonym for [^[:alnum]]
( ) do their usual precedence thing. | is the OR operator e.g. d(i|o)g matches dig or dog
For less concise information, including about backreferences, see man grep. If then you are still insufficiently confused, try man 7 regex.