I apologize for the vagueness of this question but I saw this tool over 4 years ago at this point.
I remember working with a colleague at one point who knew a bash tool or shortcut that allowed him to somehow flip the mode of the command-line interface such that instead of entering a command into the prompt, he was able to essentially freeze the screen and use the navigation arrows to specify what text output on the command-line to copy to the clipboard and I am trying to figure out what that tool was?