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,

./bootstrap  # required if ./configure is not present
./configure --prefix /usr
make
make DESTDIR="$directory" install