nushell/crates/nu-std/std/input/mod.nu

def format-event [ ] {
  let record = $in

  # Replace numeric value of raw_code with hex string
  let record = match $record {
    {raw_code: $code} => {
      $record | update raw_code {|| format number | get upperhex}
    }
    _ => $record
  }

  # Replace numeric value of raw_modifiers with binary string
  let record = match $record {
    {raw_modifiers: $flags} => {
      $record | update raw_modifiers {|| format number | get binary}
    }
    _ => $record
  }

  # Format into oneliner with `to nuon` and remove wrapping bracket pair
  $record | to nuon | str substring 1..-1
}

# Display user interface events
# 
# Press escape to stop
#
# To get individual events as records use "input listen"
export def display [
  --types(-t): list<string> # Listen for event of specified types only (can be one of: focus, key, mouse, paste, resize)
  --raw(-r) # Add raw_code field with numeric value of keycode and raw_flags with bit mask flags
] {
  let arg_types = if $types == null {
    [ key focus mouse paste resize ]
  } else if 'key' not-in $types {
    $types | append 'key'
  } else {
    $types
  }

  # To get exit key 'escape' we need to read key 
  # type events, however user may filter them out 
  # using --types and they should not be displayed
  let filter_keys = ($types != null and 'key' not-in $types)
  
  loop {
    let next_key = if $raw {
      input listen -t $arg_types -r  
    } else {
      input listen -t $arg_types
    }

    match $next_key {
      {type: key key_type: other code: esc modifiers: []} => {
        return
      }
      _ => {
        if (not $filter_keys) or $next_key.type != 'key' {
          $next_key | format-event | print
        }
      }
    }
  }
}