xrectsel is a small program that tells you the geometry of a rectangular
screen region which you have selected by dragging the mouse / pointer.
When arguments are passed to xrectsel, a limited set of % format strings
are recognized and substituted. Look at the source to see what are supported.
xrectsel requires libX11 to build.
To build and install from source,
sudo apt-get install autoconf # needed for ./bootstrap
./bootstrap # required if ./configure is not present
./configure --prefix /usr
make
make DESTDIR="$directory" install