puppet replace some lines in files

http://projects.puppetlabs.com/projects/1/wiki/Simple_Text_Patterns

define replace($file, $pattern, $replacement) { 
  exec { "/usr/bin/perl -pi -e 's/$pattern/$replacement/' '$file'": 
      onlyif => "/usr/bin/perl -ne 'BEGIN { \$ret = 1; } \$ret = 0 if 
/$pattern/ && ! /$replacement/ ; END { exit \$ret; }' '$file'", 
   } 

} 

Example:
 
replace { "/etc/bashrc": 
   file => "/etc/bashrc", 
   pattern => "PS1", 
   replacement => "PS1 DOMAINA.COM" 
}