Regular expressions patterns with grep

I know there is a lot of documentation on the topic of regular expression (like the Regexp bible, Mastering Regular Expressions, by Jeffrey Friedl ) so just some short examples I have used:

1. ls -l |egrep '.*\.[ch]p{0,2}$'
   Matches  strings with a character repeated any number of times (0+), followed by the '.' character which is escaped(to not be interpreted as the '.' which represents any character), then 'c' or 'h' followed by  0, 1, or 2 'p's. '$' means 'end of line' (the caret ('^') could be used similarly to mark the begging of line).
   But this would also match files like  "main.cp" which is not what I want so:
   
2. ls -l |egrep '.*\.(c|cpp|h|hpp)$'
   Matches just specific extensions (enclosed in "(...)").
3. ls -l |egrep -v '.*\.[ch]p{0,2}$'
   The '-v' parameter excludes the lines matching this pattern
4. ls -l |egrep -w "file123"
   Matches word "file123", but not "file1234" or "file12345". Full description from man grep :
   -w, --word-regexp
       Select  only  those  lines  containing  matches  that form whole words.  The test is that the matching substring must  either  be at  the  beginning  of  the line, or preceded by a non-word constituent character.  Similarly, it must be either at the end  of the line or followed by a non-word constituent character.  Word-constituent characters are letters, digits, and the  underscore. 
5. grep -A n -B m 'pattern'
   Shows the lines matching the pattern, and also n lines after, and m lines before the match.

Good references:

• Regular expressions quick start
• Regular exprsssions on opengroup.org

Enjoy! :)