Regex to match unique substrings

Here's a basic regex technique that I've never managed to remember. Let's say I'm using a fairly generic regex implementation (e.g., grep or grep -E). If I were to do a list of files and match any that end in either ".sty" or ".cls", how would I do that?

From stackoverflow Will Robertson

• egrep "\.sty$|\.cls$"
  

  From Peter Hoffmann

• This regex:
  \.(sty|cls)\z
  will match any string ends with .sty or .cls
  EDIT:
  for grep \z should be replaced with $ i.e. \.(sty|cls)$ as jelovirt suggested.

  From aku

• ls | grep -E "\.(sty|cls)$"
  

  • \. matches literally a "." - an unescaped . matches any character
  • (sty|cls) - match "sty" or "cls" - the | is an or and the brackets limit the expression.
  • $ forces the match to be at the end of the line

  Note, you want grep -E or egrep, not grep -e as that's a different option for lists of patterns.

  From Dave Webb