.htaccess not working for a specific case - .htaccess

Question

I am facing a strange issue while working with .htaccess file.
Here is my file:
<IfModule mod_rewrite.c>
Options +FollowSymlinks
RewriteEngine On
RewriteRule ^(admin)($|/) - [L]
RewriteRule ^$ ./web/view/
RewriteRule ^([A-Za-z0-9]+)$ ./web/view/?module=$1
RewriteRule ^([A-Za-z0-9]+)/$ ./web/view/?module=$1
RewriteRule ^([A-Za-z0-9]+)/([A-Za-z0-9]+)/([0-9]+)$ ./web/view/?module=$1&id1=$2&id2=$3
RewriteRule ^([A-Za-z0-9]+)/([A-Za-z0-9]+)/([0-9]+)/$ ./web/view/?module=$1&id1=$2&id2=$3
RewriteRule ^([A-Za-z0-9]+)/([A-Za-z0-9]+)$ ./web/view/?module=$1&id1=$2
RewriteRule ^([A-Za-z0-9]+)/([0-9]+)/$ ./web/view/?module=$1&id1=$2
ErrorDocument 404 err.php
</IfModule>
Now in the last rule, if I add [a-z] along with [0-9], I am getting a 500 error. E.g., the below line will give me 500 error:
RewriteRule ^([A-Za-z0-9]+)/([a-z0-9]+)/$ ./web/view/?module=$1&id1=$2
However, if I use A-Z, it is working fine.
RewriteRule ^([A-Za-z0-9]+)/([A-Z0-9]+)/$ ./web/view/?module=$1&id1=$2
Even [NC] is also giving me same error.
Can you help me to identify and correct this problem?

Answer 1

Now in the last rule, if I add [a-z] along with [0-9], I am getting a 500 error. E.g., the below line will give me 500 error:
The reason is because the rewrite engine is going into an infinite loop:
request URI looks like /something/id/ (note the trailing slash)
it matches the rule: RewriteRule ^([A-Za-z0-9]+)/([a-z0-9]+)/$ ./web/view/?module=$1&id1=$2
URI gets rewritten to /web/view/?module=something&id=id
new URI is put back into the rewrite engine, new URI = /web/view/
URI matches the (same) rule: RewriteRule ^([A-Za-z0-9]+)/([a-z0-9]+)/$ ./web/view/?module=$1&id1=$2
URI gets rewritten to /web/view/?module=web&id=view
repeat from step 4
You need to add a condition to prevent it from looping:
RewriteCond %{REQUEST_URI} !/web/view
RewriteRule ^([A-Za-z0-9]+)/([A-Za-z0-9]+)/$ ./web/view/?module=$1&id1=$2

Answer 2

My first instinct is to add a [L] at the end of each rewrite line, for example:
RewriteRule ^([A-Za-z0-9]+)$ ./web/view/?module=$1 [L]
This works just fine since your rewrites are independent of each other.
The second step is to consolidate each group of RewriteRule directives where the forward slash (/) is optional, so instead of:
RewriteRule ^([A-Za-z0-9]+)$ ./web/view/?module=$1
RewriteRule ^([A-Za-z0-9]+)/$ ./web/view/?module=$1
It is just as safe to say:
RewriteRule ^([A-Za-z0-9]+)/?$ ./web/view/?module=$1
The question mark (?) means 0 or 1 but not more than the preceding character, group or expression.
Lastly you may consider optimizing the group of RewriteRule directives:
<IfModule mod_rewrite.c>
Options +FollowSymlinks
RewriteEngine On
RewriteRule ^(admin)($|/) - [L]
RewriteRule ^$ ./web/view/ [L]
RewriteRule ^([A-Za-z0-9]+)/?((([A-Za-z0-9]+)/?)?(([A-Za-z0-9]+)/?)?)?$ ./web/view/?module=$1&id1=$4&id2=$6 [L]
ErrorDocument 404 err.php
</IfModule>
And as bonus information, it may be worth your while to use the QSA (query string append) flag, for example:
RewriteRule ^$ ./web/view/ [L,QSA]
You may also consider using gskinner's RegExr tool to help you create, test or troubleshoot your regular expressions.
Lasty, in your .htaccess file, depending on how the AllowOverrides directive is defined, you may be able to turn on mod_rewrite logging:
RewriteLog "/path/to/your/home/dir/rewrite.log"
RewriteLogLevel 4
However, depending on your apache server version or configuration, you may be required to use the per-module logging configuration since RewriteLog/Level is deprecated:
LogLevel alert rewrite:trace4
As a disclaimer, this level of logging will slow down your webserver, so do not enable it for too long nor on a production environment.