Small example Perl program, taken from Learning Perl (4th Edition) by Randal L. Schwartz, Tom Phoenix & brian d foy (O'Reilly Publishing, 2005).

     #!/usr/local/bin/perl

     @lines = `perldoc -u -f atan2`;

     foreach (@lines)
       {
          s/\w<([^>]+)>/\U$1/g;
  
          print;
       }