A complete guide for understanding .htaccess file and its code.

Understanding Regular Expression

**1) Period ** **.** :

This matches any single character.

Example a): c.t will match cat, cbt, cct, and so on?

2) Plus **+**:

This will repeat the previous match one or more times.

Example a): _a+_ matches _a, aa, aaa,_ and so on...

Example b): _**(**ab)+_ matches _(ab), (abab), (ababab)_, and so on?

3) Asterisk *****:

This will repeat the previous match zero or more times.

Example a): _a*_ matches, empty strings, _a, aa, aaa,_ and so on...

Example b): (_ab)*_ matches empty strings**,** _ab, abab, ababab,_ and so on?

4) Question **?**:

This will do an optional match.

**Example a): ** colo**u**? r  will match color and colour.

5) Backslash **\**:

This will escape the next character.

Example a): \. will match .(dot) and not any single character.

6) Tilde (or anchor) **^**: 

This will match the beginning of the string

**Example a): ** ^a will match any string starting with a.

7) Dollar Sign **$**:

This will match the beginning of the string

Example a): a$ will match any string ending with a.

8) Parenthesis **( )**:

This will group several characters into a single unit.

Example a): _**(**ab)+_ matches _(ab), (abab), (ababab),_ and so on?

Example b): _**(**ab)*_ matches empty strings**,** _ab, abab, ababab,_ and so on?

8) Bracket **[ ]**:

This will match one of the characters.

Example a): c[abc]t will match cat, cbt. cct.

9) Bracket **[ ^ ]**:

This is negative character class and will match any character which is not present there.

Example a): c[^a]t will not match cat but will match cbt, cct, cdt, etc.

RewriteEngine On

mod_rewrite an Apache module which allows us to rewrite URL requests that come into our server.

Uses: 

1. Removing index.php in Codeigniter Project.
2. Forcing https://
3. Convert URL to lowercase.
4. Forcing www for each request.
5. Redirecting from one subdirectory to a different one.
   1. https://example.com/folder1  ==> https://example.com/folder2
6. Redirect request to a subdirectory
   1. https://example.com/image.jpg ==> https://example.com/folder/image.jpg

RewriteCond %{REQUEST_FILENAME} !-f

RewriteCond %{REQUEST_FILENAME} !-d

RewriteRule ^(.*)$ index.php?/$0 [PT,L,QSA]