Linux Shell Scripting Cookbook - Third Edition

Adding a delay

Let's say you are using repeat() to download a file from the Internet which is not available right now, but will be after some time. An example would be as follows:

repeat wget -c http://www.example.com/software-0.1.tar.gz

This script will send too much traffic to the web server at www.example.com, which causes problems for the server (and maybe for you, if the server blacklists your IP as an attacker). To solve this, we modify the function and add a delay, as follows:

repeat() { while :; do $@ && return; sleep 30; done }

This will cause the command to run every 30 seconds.