User:Swapnil durgade/Regular Expressions Notes

      c          matches the non-metacharacter c.
      \c         matches the literal character c.
      .          matches any character including newline.
      ^          matches the beginning of a string.
      $          matches the end of a string.
      [abc...]   character class, matches any of the characters abc....
      [^abc...]  negated character class, matches any character except abc....
      r1|r2      alternation: matches either r1 or r2.
      r1r2       concatenation: matches r1, and then r2.
      r+         matches one or more r's.
      r*         matches zero or more r's.
      r?         matches zero or one r's.
      (r)        grouping: matches r.
      r{n}
      r{n,}
      r{n,m}     One  or two numbers inside braces denote an interval expres-
                 sion.  If there is one number in the braces,  the  preceding
                 regular  expression r is repeated n times.  If there are two
                 numbers separated by a comma, r is repeated n  to  m  times.
                 If  there  is  one  number  followed  by  a comma, then r is
                 repeated at least n times.
                 Interval expressions are only available if either --posix or
                 --re-interval is specified on the command line.
      \y         matches  the empty string at either the beginning or the end
                 of a word.
      \B         matches the empty string within a word.
      \<         matches the empty string at the beginning of a word.
      \>         matches the empty string at the end of a word.
      \w         matches any word-constituent character  (letter,  digit,  or  underscore).
      \W         matches any character that is not word-constituent.
      \'         matches the empty string at the end of a buffer.