So I was messing around with getting a few logging systems setup for a web app I’m writing and after a while these log files started to grow in size to the point that it was difficult to find the relevant data quickly. I needed a quick way to empty a file without deleting it. Here’s the trick I learned:

// First let’s put some text into a file $ echo “test” > filename.log

// Let’s display it
$ cat filename.log

// and empty it
$ cat /dev/null > filename.log

Basically ‘cat’ reads the file contents of whatever you specify, in this case /dev/null which is empty. It then uses the ’>’ character to push the contents of /dev/null (empty) to filename.log, overwriting anything that currently exists in it.