How does nginx implement if nested method examples

nginx does not support nesting of if, nor does it allow the use of logical judgments in if. The following error is reported:

[

nginx: [emerg] "if" directive is not allowed

]

When the business needs more than one conditional judgment, it can be implemented with intermediate variables

For example, our website has several sub-domains in pc terminal, while the mobile terminal only has one domain name. The corresponding relationship is as follows:

www.test.com -- > m.test.com sub1.test.com -- > m.test.com/sub1 sub2.test.com -- > m.test.com/sub2 sub3.test.com -- > m.test.com/sub3

To achieve the effect: when the mobile terminal access pc domain name 301 jump to the corresponding mobile terminal domain name

The rewriting rules for nginx are as follows:

#  Whether it is a mobile terminal 
set $mobile 0;
if ($http_user_agent ~* (mobile|nokia|iphone|ipad|android|samsung|htc|blackberry)) {
  set $mobile 1;
}

#  Get subdomain 
set $prefix 1;
if ($host ~* "sub1.test.com") {
  set $prefix 2;
}
if ($host ~* "sub2.test.com") {
  set $prefix 3;
}
if ($host ~* "sub3.test.com") {
  set $prefix 4;
}
set $sign "${mobile}${prefix}";
if ($sign = 11) {
  rewrite ^(.*) http://m.test.com$1 permanent;
}
if ($sign = 12) {
  rewrite ^(.*) http://m.test.com/sub1$1 permanent;
}
if ($sign = 13) {
  rewrite ^(.*) http://m.test.com/sub2$1 permanent;
}
if ($sign = 14) {
  rewrite ^(.*) http://m.test.com/sub3$1 permanent;
}