[edit] uninitialized_variable_warn

Syntax: uninitialized_variable_warn on | off
Default: on
Context: http
server
location
if
Reference: uninitialized_variable_warn


Enables or disables logging of warnings about noninitialized variables.

[edit] Internal implementation

Internally, the rewrite directives are compiled at the time the configuration file is loaded into internal codes, usable during the request by the interpreter.

This interpreter is a simple stack virtual machine. For example, the directive:

location /download/ {
  if ($forbidden) {
    return   403;
  }
  if ($slow) {
    limit_rate  10k;
  }
  rewrite  ^/(download/.*)/media/(.*)\..*$  /$1/mp3/$2.mp3  break;
}

will be compiled into this sequence:

  variable $forbidden
  checking to zero
  recovery 403
  completion of entire code
  variable $slow
  checking to zero
  checkings of regular expression
  copying "/"
  copying $1
  copying "/mp3/"
  copying $2
  copying ".mp3"
  completion of regular expression
  completion of entire sequence

Note that there is no code for directive limit_rate, since it does not refer to module ngx_http_rewrite_module. The "if" block exists in the same part of the configuration as the "location" directive.

If $slow is true, then what's inside the "if" block is evaluated, and in this configuration limit_rate it is equal to 10k.

Directive:

  rewrite  ^/(download/.*)/media/(.*)\..*$  /$1/mp3/$2.mp3  break;

It is possible to reduce the sequence, if in the regular expression we include the first slash inside the parentheses:

  rewrite  ^(/download/.*)/media/(.*)\..*$  $1/mp3/$2.mp3  break;

then the sequence will appear like this:

  checking regular expression
  copying $1
  copying "/mp3/"
  copying $2
  copying ".mp3"
  completion of regular expression
  completion of entire code

[edit] References

Original Documentation

PCRE Man Page in Plain Text


RegexOne» Learn regular expressions with simple, interactive examples.

RegexPal — a JavaScript regular expression tester


Module: HttpRewriteModule