title: What special characters must be escaped in regular expressions?
body: <p>I am tired of always trying to guess, if I should escape special characters like '<code>()[]{}|</code>' etc. when using many implementations of regexps.</p>
  
  <p>It is different with, for example, Python, sed, grep, awk, Perl, rename, Apache, find and so on.
  Is there any rule set which tells when I should, and when I should not, escape special characters? Does it depend on the regexp type, like PCRE, POSIX or extended regexps?</p>