slop

Get a selection of the screen. More information: https://github.com/naelstrof/slop.

• Wait for the user to make a selection and output its geometry to stdout:
  slop
• Double click, rather than click and drag, to draw a selection:
  slop -D
• Highlight the selection rather than outlining it:
  slop -l
• Specify the output format:
  slop -f {{format_string}}
• Specify the selection rectangle's color:
  slop -c {{red}},{{green}},{{blue}},{{alpha}}