Download and extract the latest release. Then, re-read what's in there if it's different than the following:

To install, just execute ./install.sh. If you wish to install psgrep somewhere other than /usr/local/bin, set the $PREFIX variable like so:

PREFIX=/usr sudo ./install.sh

The default $PREFIX is /usr/local

If you, for example, install psgrep to your home directory, don't forget to set your PATH to include ~/bin as well as your MANPATH (or ~/.manpath) to include ~/share/man.

For usage information, run

man psgrep