String manipulation vs Regexps

Question

We are often told that Regexps are slow and should be avoided whenever possible.

However, taking into account the overhead of doing some string manipulation oneself (

Answer 1

A nice feature of manipulating text with regular expressions is that patterns are high-level and declarative. This leaves the implementation considerable room for optimization such as factoring out the longest common prefix or using Boyer-Moore for static strings. Concise notation makes for quicker reading by experts. I understand immediately what

if (s/^(.)//) {
  ...
}

is doing, and index($_, 0, 1) = "" looks noisy in comparison.

Rather than the lower bound, the important consideration for regular expressions is the upper bound. It's a powerful tool, so people believe it's capable of correctly extracting tokens from XML, email addresses, or C++ programs and don't realize that an even more powerful tool such as a parser is necessary.