Programming Perl, 4th Edition

Time Efficiency

• Use hashes instead of linear searches. For example, instead of searching through @keywords to see whether $_ is a keyword, construct a hash with:

  my %keywords;
  for (@keywords) {
      $keywords{$_}++;
  }

  Then you can quickly tell if $_ contains a keyword by testing $keyword{$_} for a nonzero value.

• Avoid subscripting when a foreach or list operator will do. Not only is subscripting an extra operation, but if your subscript variable happens to be in floating point because you did arithmetic, an extra conversion from floating point back to integer is necessary. There’s often a better way to do it. Consider using foreach, shift, and splice operations. Consider saying use integer.

• Avoid goto. It scans outward from your current location for the indicated label.

• Avoid printf when print will do.

• Avoid $& and its two buddies, $` and $'. Any occurrence in your program causes all matches to save the searched string for possible future reference. However, once you’ve blown it, it doesn’t hurt to have more of them. Perl v5.10 introduced the per-match variables with the /p (see Chapter 5), so you don’t have to either suffer or give up features.

• Avoid using eval on a string. An eval of a string (although not of a BLOCK) forces recompilation every time through. The Perl parser is pretty fast for a parser, but that’s not saying much. Nowadays there’s almost always a better way to do what you want anyway. In particular, any code that uses eval merely to construct variable names is obsolete since ...