. Matches any character except new line
[a-z0-9] Matches any single character of set
[^a-z0-9] Matches any single character not in set
\d Matches a digit, same as [0-9]
\D Matches a non-digit, same as [^0-9]
\w Matches an alphanumeric (word) character [a-zA-Z0-9_]
\W Matches a non-word character [^a-zA-Z0-9_]
\s Matches a whitespace char (space, tab, newline etc)
\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, because...
\nnn Matches an ASCII character with an octal value nnn
\xnn Matches an ASCII character with a hex value nn
\cX Matches an ASCII control character
\metachar Matches the character itself (\|,\.,\* etc)
(abc) Remembers the match for later backreferences
\1 Matches whatever first set of parens matched
\2 Matches whatever second set of parens matched
\3 ..etc etc
x? Matches 0 or 1 x's, where x is any of the above
x* Matches 0 or more x's
x+ Matches 1 or more 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
fee|fie|foe Matches one of fee, fie or foe
\b Matches a word boundary (outside [] only)
\B Matches a non-word boundary
^ Anchors match to the beginning of a line or string
$ Anchors match to the end of a line or string
A good general discussion of PERL can be found in
Wall, L. & Schwartz, R. (1992) Programming Perl. O'Reilly & Associates, Sebastapol, CA, US.