Parsing a Web Server Log File (Perl Cookbook, 2nd Edition)

## 20.12. Parsing a Web Server Log File

### 20.12.1. Problem

You want to extract selected information from a web server log file.

### 20.12.2. Solution

Pull apart the log file as follows:

>     while (<LOGFILE>) {
>       my ($client, $identuser, $authuser, $date, $time, $tz, $method,
>           $url, $protocol, $status, $bytes) =
>       /^(\S+) (\S+) (\S+) \[([^:]+):(\d+:\d+:\d+) ([^\]]+)\] "(\S+) (.*?) (\S+)"
>           (\S+) (\S+)$/;
>       # ...
>     }

### 20.12.3. Discussion

This regular expression pulls apart entries in Common Log Format, an informal standard that most web servers adhere to. The fields are listed in Table 20-1.

#### Table 20-2. Common Log Format fields

Field | Meaning
--- | ---
client | IP address or hostname of browser's machine
identuser | If IDENT (RFC 1413) was used, what it returned
authuser | If username/password authentication was used, whom they logged in as
date | Date of request (e.g., 01/Mar/1997)
time | Time of request (e.g., 12:55:36)
tz | Time zone (e.g., -0700)
method | Method of request (e.g., GET, POST, or PUT)
url | URL in request (e.g., /~user/index.html)
protocol | HTTP/1.0 or HTTP/1.1
status | Returned status (200 is okay, 500 is server error)
bytes | Number of bytes returned (could be "`-`" for errors, redirects, and other non-document transfers)

Other formats include the referrer and agent information. The pattern needs only minor changes to work with other log file formats. Beware that spaces in the URL field are not escaped, so we can't use `\S*` to extract the URL. `.*` would cause the regex to match the entire string and then backtrack until it could satisfy the rest of the pattern. We use `.*?` and anchor the pattern to the end of the string with `$` to make the regular expression engine initially match nothing but then add characters until the entire pattern is satisfied.

### 20.12.4. See Also

The CLF spec at http://www.w3.org/Daemon/User/Config/Logging.html

Copyright © 2003 O'Reilly & Associates. All rights reserved.