Unix Line Discard

Type C-u (i.e. ctrl+u) in Bash or Zsh to discard the current line of input. To read more about it, enter man bash and then type /unix-line-discard to locate the relevant section of the manual. Here is an excerpt:

unix-line-discard (C-u)
       Kill backward from point to the beginning of the line.
       The killed text is saved on the kill-ring.

Similarly, for Zsh, type man zshzle and then type /kill-whole-line. We find this:

kill-whole-line (^U) (unbound) (unbound)
       Kill the current line.

By the way, Emacs-style key sequence like C-a C-k works too.

Furthermore, it is quite likely that C-u is mapped to delete the current line of input in the terminal itself. To confirm this, type the command stty -a and check the output. If the output contains the text kill = ^U, then typing C-u anytime in the terminal would delete the current line of input. This would happen regardless of what program is running in the terminal. For example, programs like cat, sbcl, etc. do not support key sequences like C-a, C-k, C-u, etc. the way Bash or Zsh does. Despite this limitation, typing C-u in sbcl would delete the current line of input if the output of stty -a indicates that the terminal has mapped this key sequence to the operation of deleting the current line.