head to tail

Shell (~bash) - OS X, Windows, Linux

Use head or tail to dump the beginning, or end of a file, respectively, to STDOUT.

The default number of lines to show for both head and tail is 10.

For example, say you’ve got a log file and you’d like to see the first five entries, to make sure it’s from the session you’re trying to debug:

 head -5 /path/to/log.txt

 > 2012-06-07 05:45:23 Application Started
 > 2012-06-07 05:45:25 Database Service Started
 > 2012-06-07 05:45:25 Login Service Started
 > 2012-06-07 05:45:26 HTTP Server Started
 > 2012-06-07 05:45:26 Waiting for HTTP Client Connections

Now, to look at the last 50, so we can see everything that led up to the event we care about:

tail -50 /path/to/log.txt

 > -snip-
 > 2012-06-07 05:55:16 log log log... log log
 > 2012-06-07 05:55:19 more log stuff
 > 2012-06-07 05:55:19 KABOOM!

I use head and tail quite a bit to look at the beginnings and ends of files (particularly long XML files) so I can make the right data is being sent at the beginning and end of the file.