ntail

A tail(1)-like utility for nginx log files that supports parsing, filtering and formatting of individual log lines (in nginx's so-called "combined" log format).

Check it out, yo!

Instead of this...


<span style="color:white;">$ tail -f /var/log/nginx/access.log</span>
<span style="color: green;">192.0.32.10 - - [21/Jan/2011:14:07:34 +0000] "GET / HTTP/1.1" 200 3700 "-" "Mozilla/5.0 (X11; U; Linux x86_64; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.237 Safari/534.10" "-"</span>
<span style="color: green;">192.0.32.10 - - [21/Jan/2011:14:07:34 +0000] "GET /nginx-logo.png HTTP/1.1" 200 370 "http://localhost/" "Mozilla/5.0 (X11; U; Linux x86_64; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.237 Safari/534.10" "-"</span>
<span style="color: green;">192.0.32.10 - - [21/Jan/2011:14:07:34 +0000] "GET /poweredby.png HTTP/1.1" 200 3034 "http://localhost/" "Mozilla/5.0 (X11; U; Linux x86_64; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.237 Safari/534.10" "-"</span>
<span style="color: green;">192.0.32.10 - - [21/Jan/2011:14:07:34 +0000] "GET /favicon.ico HTTP/1.1" 404 3650 "-" "Mozilla/5.0 (X11; U; Linux x86_64; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.237 Safari/534.10" "-"</span>
<span style="color: green;">192.0.32.10 - - [21/Jan/2011:14:19:04 +0000] "GET /nginx-logo.png HTTP/1.1" 304 0 "-" "Mozilla/5.0 (X11; U; Linux x86_64; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.237 Safari/534.10" "-"</span>
<span style="color:white;">$ _</span>

... you get this:


<span style="color:white;">$ tail -f /var/log/nginx/access.log <strong>| ntail</strong></span>
<span style="color: green;">2011-01-21 14:07:34 -       192.0.32.10 - 200 - GET / - (Chrome, Linux) - -</span>
<span style="color: green;">2011-01-21 14:07:34 -       192.0.32.10 - 200 - GET /nginx-logo.png - (Chrome, Linux) - localhost</span>
<span style="color: green;">2011-01-21 14:07:34 -       192.0.32.10 - 200 - GET /spanoweredby.png - (Chrome, Linux) - localhost</span>
<span style="color: red;">2011-01-21 14:07:34 -       192.0.32.10 - 404 - GET /favicon.ico - (Chrome, Linux) - -</span>
<span style="color: orange;">2011-01-21 14:19:04 -       192.0.32.10 - 304 - GET /nginx-logo.png - (Chrome, Linux) - -</span>
<span style="color:white;">$ _</span>

Installation

Installing the gem also installs the ntail executable, typically as /usr/bin/ntail or /usr/local/bin/ntail:

$ gem install ntail

To ensure easy execution of the ntail script, add the actual installation directory to your shell's $PATH variable.

Basic Usage

process an entire nginx log file and print each parsed and formatted line to STDOUT
```
$ ntail /var/log/nginx/access.log
```
process an entire nginx log file and pipe each parsed and formatted line into a browser (depends on the optional bcat gem)
```
$ ntail /var/log/nginx/access.log | bcat
```
tail an "active" nginx log file and print each new line to STDOUT (stop with ^C)
```
$ tail -f /var/log/nginx/access.log | ntail
```
tail an "active" nginx log file and pipe each new line into a browser (stop with ^C)
```
$ tail -f /var/log/nginx/access.log | ntail | bcat
```

Advanced Examples

read from STDIN and print each line to STDOUT (stop with ^D)
```
$ ntail
```
read from STDIN and print out the length of each line (to illustrate -e option)
```
$ ntail -e 'puts size'
```
read from STDIN but only print out non-empty lines (to illustrate -f option)
```
$ ntail -f 'size != 0'
```
the following invocations behave exactly the same (to illustrate -e and -f options)
```
$ ntail
$ ntail -f 'true' -e 'puts self'
```

print out all HTTP requests that are coming from a given IP address

$ ntail -f 'remote_address == "208.67.222.222"' /var/log/nginx/access.log

find all HTTP requests that resulted in a '5xx' HTTP error/status code (e.g. Rails 500 errors)
```
$ gunzip -S .gz -c access.log-20101216.gz | ntail -f 'server_error_status?'
```

generate a summary report of HTTP status codes, for all non-200 HTTP requests

$ ntail -f 'status != "200"' -e 'puts status' access.log | sort | uniq -c
76 301
16 302
 2 304
 1 406

print out GeoIP country and city information for each HTTP request (depends on the optional geoip gem)

$ ntail -e 'puts [to_country_s, to_city_s].join("\t")' /var/log/nginx/access.log
United States   Los Angeles
United States   Houston
Germany         Berlin
United Kingdom  London

print out the IP address and the corresponding host name for each HTTP request (slows things down considerably, due to nslookup call)

$ ntail -e 'puts [remote_address, to_host_s].join("\t")' /var/log/nginx/access.log
66.249.72.196   crawl-66-249-72-196.googlebot.com
67.192.120.134  s402.pingdom.com
75.31.109.144   adsl-75-31-109-144.dsl.irvnca.sbcglobal.net

parse an access log file, and pipe its raw output (indirectly - via the parsed.log file) into the gltail realtime logfile visualizer
```
$ ntail -v --raw --sleep 0.1 /var/log/nginx/access.log > parsed.log
```

TODO

implement a native "-f" option for ntail, similar to that of tail(1), using e.g. flori's file-tail gem
implement a "-i" option ("ignore exceptions"/"continue processing"), if handling a single line raises an exception
or indeed a reverse "-r" option ("re-raise exception"), to immediately stop processing and raising the exception for investigation
implement (better) support for custom nginx log formats, in addition to nginx's default "combined" log format (as well as Apache's various log formats)

Acknowledgements

ntail's parsing feature is inspired by an nginx log parser written by Richard Taylor (moomerman)
parsing and expanding ntail's formatting string is done using nathansobo's quite brilliant treetop gem
ntail's raw line output is compatible with Fudge's fun and useful gltail gem, as well as the quite amazing logstalgia
kudos to Ed James (edjames) for recommending the use of instance_eval to clean up the DSL
ntail's HTML formatting was requested/suggested by Phil Berryman and implemented whilst listening to Leftism, the Leftfield album recommended to me by Alastair Douglas

Contributing to ntail

Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet
Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it
Fork the project
Start a feature/bugfix branch
Commit and push until you are happy with your contribution
Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.