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Regular Expressions for URL Rewriting


A complete guide to regular expressions is rather beyond the scope of this article. However, important points to remember are that the entire pattern is treated as a regular expression, so always be careful of characters that are “special” characters in regular expressions such as .(DOT stands for any character).
  • . (any character)
  • * (zero of more of the preceding)
  • + (one or more of the preceding)
  • {} (minimum to maximum quantifier)
  • ? (ungreedy modifier)
  • ! (at start of string means “negative pattern”)
  • ^ (start of string, or “negative” if at the start of a range)
  • $ (end of string)
  • [] (match any of contents)
  • - (range if used between square brackets)
  • () (group, backreferenced group)
  • | (alternative, or)
  • \ (the escape character itself)
Flags
Flags are added to the end of a rewrite rule to tell Apache how to interpret and handle the rule. They are comma-separated, and contained in square brackets. Here’s a list of the flags, with their meanings
  • C (chained with next rule)
  • CO=cookie (set specified cookie)
  • E=var:value (set environment variable var to value)
  • F (forbidden – sends a 403 header to the user)
  • G (gone – no longer exists)
  • H=handler (set handler)
  • L (last – stop processing rules)
  • N (next – continue processing rules)
  • NC (case insensitive)
  • NE (do not escape special URL characters in output)
  • NS (ignore this rule if the request is a subrequest)
  • P (proxy – i.e., apache should grab the remote content specified in the substitution section and return it)
  • PT (pass through – use when processing URLs with additional handlers, e.g., mod_alias)
  • R (temporary redirect to new URL)
  • R=301 (permanent redirect to new URL)
  • QSA (append query string from request to substituted URL)
  • S=x (skip next x rules)
  • T=mime-type (force specified mime type)

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