Simple robot.txt tutorial

Saman · Post by **Saman** » Sat Mar 13, 2010 7:07 am

The simplest robots.txt file uses two rules:

User-agent: the robot the following rule applies to
Disallow: the URL you want to block

These two lines are considered a single entry in the file. You can include as many entries as you want. You can include multiple Disallow lines and multiple user-agents in one entry.

Each section in the robots.txt file is separate and does not build upon previous sections. For example:

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User-agent: *
Disallow: /folder1/

User-Agent: Googlebot
Disallow: /folder2/

In this example only the URLs matching /folder2/ would be disallowed for Googlebot.

User-agents and bots
A user-agent is a specific search engine robot. The Web Robots Database lists many common bots. You can set an entry to apply to a specific bot (by listing the name) or you can set it to apply to all bots (by listing an asterisk). An entry that applies to all bots looks like this:

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User-agent: *

Blocking user-agents
The Disallow line lists the pages you want to block. You can list a specific URL or a pattern. The entry should begin with a forward slash (/).

To block the entire site, use a forward slash.
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```
Disallow: /
```
To block a directory and everything in it, follow the directory name with a forward slash.
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```
Disallow: /junk-directory/ 
```
To block a page, list the page.
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```
Disallow: /private_file.html
```
To remove a specific image from Google Images, add the following:
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```
User-agent: Googlebot-Image
Disallow: /images/dogs.jpg 
```
To remove all images on your site from Google Images:
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```
User-agent: Googlebot-Image
Disallow: / 
```
To block files of a specific file type (for example, .gif), use the following:
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```
User-agent: Googlebot
Disallow: /*.gif$
```

Note that directives are case-sensitive. For instance, Disallow: /junk_file.asp would block http://www.example.com/junk_file.asp, but would allow http://www.example.com/Junk_file.asp. Googlebot will ignore white-space (in particular empty lines)and unknown directives in the robots.txt.

Sitemap files can also be submitted using robot.txt. Advanced search engines like Google support this feature.

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Sitemap: http://www.example.com/sitemap-host1.xml
Sitemap: http://www.example.com/sitemap-host2.xml

Pattern matching
Not all search engines respects some pattern matching (Again Google supports this feature).

To match a sequence of characters, use an asterisk (*). For instance, to block access to all subdirectories that begin with private:
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```
User-agent: Googlebot
Disallow: /private*/
```
To block access to all URLs that include a question mark (?) (more specifically, any URL that begins with your domain name, followed by any string, followed by a question mark, followed by any string):
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```
User-agent: Googlebot
Disallow: /*?
```
To specify matching the end of a URL, use $. For instance, to block any URLs that end with .xls:
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```
User-agent: Googlebot 
Disallow: /*.xls$
```
You can use this pattern matching in combination with the Allow directive. For instance, if a ? indicates a session ID, you may want to exclude all URLs that contain them to ensure Googlebot doesn't crawl duplicate pages. But URLs that end with a ? may be the version of the page that you do want included. For this situation, you can set your robots.txt file as follows:
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```
User-agent: *
Allow: /*?$
Disallow: /*?
```
The Disallow: / *? directive will block any URL that includes a ? (more specifically, it will block any URL that begins with your domain name, followed by any string, followed by a question mark, followed by any string).

The Allow: /*?$ directive will allow any URL that ends in a ? (more specifically, it will allow any URL that begins with your domain name, followed by a string, followed by a ?, with no characters after the ?).