How to only redirect urls located in a nginx Map - redirect

Question

I am in the process of moving my blog from a.com to b.com. Now I want to tell Google /bookmarks that all blogposts (around 100) have been moved to b.com. I only want to redirect the blogposts and nothing else.
After reading about the map module in nginx I tried the following:
map_hash_bucket_size 128;
map $uri $new {
/post http://b.com/post
# (repeated for all 100 posts)
}
And when I put the following line inside the server block:
rewrite ^ $new redirect;
It will redirect all 100 posts but all the other pages on my domain will error with: 302 Found.
Here is my whole server block inside the config:
server {
listen 80;
server_name b.com;
root /my/old/path/;
index index.html;
location = /favicon.ico {
log_not_found off;
access_log off;
}
location = /robots.txt {
allow all;
log_not_found off;
access_log off;
}
# Deny all attempts to access hidden files such as .htaccess, .htpasswd, .DS_Store (Mac).
location ~ /\. {
deny all;
access_log off;
log_not_found off;
}
location ~* \.(js|css|png|jpg|jpeg|gif|ico)$ {
expires max;
log_not_found off;
}
# example.com/index gets redirected to example.com/
location ~* ^(.*)/index$ {
return 301 $scheme://$host$1/;
}
# example.com/foo/ loads example.com/foo/index.html
location ~* ^(.*)/$ {
try_files $1/index.html #backend;
}
# example.com/a.html gets redirected to example.com/a
location ~* \.html$ {
rewrite ^(.+)\.html$ $scheme://$host$1 permanent;
}
# anything else not processed by the above rules:
# * example.com/a will load example.com/a.html
# * or if that fails, example.com/a/index.html
location / {
try_files $uri.html $uri/index.html $uri #backend;
}
# default handler
# * return error or redirect to base index.html page, etc.
location #backend {
try_files /404.html 404;
}
location ~ \.php$ {
expires off;
try_files $uri =404;
fastcgi_split_path_info ^(.+\.php)(/.+)$;
#NOTE: You should have "cgi.fix_pathinfo = 0;" in php.ini
include fastcgi_params;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_intercept_errors on;
fastcgi_pass php;
}
# apply the rewrite map
rewrite ^ $new redirect;
}
I am thinking the map interferes with the try_files call for location \ (which I need).

Answer 1

I found a solution for your problem on serverfault:
This is probably failing because you're trying to redirect all
requests, whether they matched something in the map or not.
To prevent this, check to see if there was a match first.
if ($new) {
return 301 $new;
}
So replace
rewrite ^ $new redirect;
with
if ($new) {
return 301 $new;
}
And you should be good to go

Answer 2

I have not been able to figure out how to do this with map, as it's still quite a string module to me. Now I've just put all the rewrites in a list inside my server block (above all location blocks), which is probably very slow. Now the file looks like this:
server {
listen 80;
server_name a.com;
root /my/old/path/;
index index.html;
rewrite /post http://b.com/post
# (x100)
location = /favicon.ico {
log_not_found off;
access_log off;
}
location = /robots.txt {
allow all;
log_not_found off;
access_log off;
}
# Deny all attempts to access hidden files such as .htaccess, .htpasswd, .DS_Store (Mac).
location ~ /\. {
deny all;
access_log off;
log_not_found off;
}
location ~* \.(js|css|png|jpg|jpeg|gif|ico)$ {
expires max;
log_not_found off;
}
# example.com/index gets redirected to example.com/
location ~* ^(.*)/index$ {
return 301 $scheme://$host$1/;
}
# example.com/foo/ loads example.com/foo/index.html
location ~* ^(.*)/$ {
try_files $1/index.html #backend;
}
# example.com/a.html gets redirected to example.com/a
location ~* \.html$ {
rewrite ^(.+)\.html$ $scheme://$host$1 permanent;
}
# anything else not processed by the above rules:
# * example.com/a will load example.com/a.html
# * or if that fails, example.com/a/index.html
location / {
try_files $uri.html $uri/index.html $uri #backend;
}
# default handler
# * return error or redirect to base index.html page, etc.
location #backend {
try_files /404.html 404;
}
location ~ \.php$ {
expires off;
try_files $uri =404;
fastcgi_split_path_info ^(.+\.php)(/.+)$;
#NOTE: You should have "cgi.fix_pathinfo = 0;" in php.ini
include fastcgi_params;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_intercept_errors on;
fastcgi_pass php;
}
# apply the rewrite map
rewrite ^ $new redirect;
}