How to find string and replace some string between { … }?

You only need to change the port in the /test/v2.0.0 block:

server {
    location /test/v2.0.3 {
        modsecurity on;
        proxy_pass http://10.1.0.6:3000;
    }
    location /test/v2.0.0 {
        modsecurity on;
        proxy_pass http://10.1.0.6:3000;
    }
}

sed '0,/:[0-9].*;/{s/:[0-9].*;/:5555;/}' test.nginx
– changes the first match

sed '/.*location.*\/test\/v2.0.0\/.*:[0-9].*;/{s/:[0-9].*;/:5555;/}' test.nginx
– doesn’t change anything

sed 's/.*location.*\/test\/v2.0.0\/.*:[0-9].*;/:5555;/' test.nginx
– doesn’t change anything

P.S.:

What the task sounds like:
Find location /test/v2.0.0.0 preceded by any character except #, select everything in the brackets { }, find the port string :3000; between them, replace it with the specified one.

Output:

server {
    location /test/v2.0.3 {
        modsecurity on;
        proxy_pass http://10.1.0.6:3000;
    }
    location /test/v2.0.0 {
        modsecurity on;
        proxy_pass http://10.1.0.6:5555;
    }
}

>Solution :

You can use the below awk to achieve your result.

awk '
/location \/test\/v2.0.0/ {flag=1}
flag && /proxy_pass/ {sub(/:[0-9]+;/, ":5555;")}
/}/ {flag=0}
{print}
' your_file

The command will:

1. Set a flag when the line containing location /test/v2.0.0 is found.
2. If the flag is set and the line contains proxy_pass, it will substitute the port number with 5555.
3. When the closing brace(}) is found, the flag is unset and each line will be printed.

demo here