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Accepted
Howard
Asked: 2012-11-29 09:07:48 +0800 CST

Set a default variable in nginx with set

  • 772

In nginx I can use set to define a variable, but is it possible to define a default?

e.g.

set $foo bar if $foo is not defined
nginx

3 Answers

  1. Best Answer
    map $foo $new_foo {
    default  $foo;
    ''       bar;
}

    or

    if ($foo = '') {
    set $foo bar;
}
    • 17

  2. This also works:

    map $foo $foo {
    default '';
}
map $foo $bar {
    default '';
    'bar' 'bar';
    'foo' $foo;   <----- nginx: [emerg] unknown "foo" variable
}

    map $foo $foo {} solves error nginx: [emerg] unknown "foo" variable - just doesn't look right - but it works.

    Note: map must be in block http {} (nginx/conf.d)

    • 0

  3. map $foo $foo {} gives me cycle while evaluating variable "foo" error message in the nginx error log.

    Now,

    map $foo $foo_with_default {
  default 'bar';
  ~. $foo;
}

    does work and it's also semantically correct: if the regular expression matches anything then the result will be $foo if it doesn't then there are no characters to match so it becomes bar. I do not think the configuration syntax for nginx makes it possible to distinguish between an empty string and an undefined variable. I believe you need openresty and a nil check for that.

    • 0