9.9.  Additional Operators

The unary postfix operators ? and + do not allow us to define additional languages, but they often make it easier to express languages.

R? stands for | R

R+ stands for L(R) L(RR) L(RRR) ...

Examples:

• Examples:
• Find all the words that end in ``dous''.

  % grep '.*dous' words    # false, why?
  
  % grep '^.*dous$' words
  hazardous
  horrendous
  stupendous
  tremendous
  

• Find all words that have two ``x''.

  % grep '^[^x]*x[^x]*x[^x]*' words
  executrix
  Exxon
  xerox
  

• Find all words that have two times alternating [xyz] and [^xyz].

  %  egrep '^.*[xyz][^xyz][xyz][^xyz].*' words
  bryozoa
  oxeye
  polygynous
  Polyhymnia
  polytypy
  zazen
  

• Find all words that have a vowel ( )) followed by a consonante ( ) followed by followed by followed by .

  % grep '^.*\([aeiou]\)\([^aeiou]\)\1\2\1.*' words
  banana
  homomorphic
  homomorphism
  prosopopoeia
  rococo
  Tananarive
  

• Find all words that includes the word 'suny'.

  % grep '^.*s[^s]*u[^su]*n[^sun]*y[^suny]*' words
  sanguinary
  scrutiny
  simultaneity
  substitutionary
  sundry
  sunny
  superlunary
  supplementary
  suzerainty
  

• Find every word that have double ``a'' or double ``b'' followed by a ``e'' or ``o'' followed by a ``c'' or ``d''.

%  egrep '(aa|bb)(e|o)(c|d)' words
Lubbock

Last modified: 27/July/98 (12:14)