Perl Regular Expressions 
.  Matches any character except newline 
[az09]  Matches any single character of set 
[^az09]  Matches any single character not in set 
\d  Matches a digit, same as [09] 
\D  Matches a nondigita, same as [^09] 
\w  Matches an alphanumeric (word) character [azAZ09] 
\W  Matches a nonword character [^azAZ09] 
\s  Matches a whitespar characteer (space, tab, newline) 
\S  Matches a nonwhitespace character 

\n  Matches a newline 
\r  Matches a return 
\t  Matches a tab 
\f  Matches a formfeed 
\b  Matches a backspace (inside [ ] only) 
\0  Matches a null character 
\000  Also matches a null character becasue... 
\nnn  Matches an ASCII character of that octal value 
\cX  Matches an ASCII control character 
\metachar  Matches the character itself (\, \., \*...) 

(abc)  Remembers the match for later backreference 
\1  Matches whatever first of parens matched 
\2  Matches whatever second set of parens matched 
\3  and so on... 

x?  Matches 0 or 1 x's, where x is any of above 
x*  Matches 0 or more x's 
x+  Matches 1 or more x's 
x{m}  Matches at exactly m x's 
x{m,}  Matches at least m x's 
x{m, n}  Matches at least m x's but no more than n 

abc  Matches all of a, b, and c in order 
feefiefoe  Matches one of fee, fie or foe 

\b  Matches a word boundry (outside [ ] only) 
\B  Matches a nonword boundry 
^  Anchors match to the beginning of a line or string 
$  Anchors match to the end of a line or string 