Removes a line from ~/.ssh/known_hosts. Takes a number as an argument or prompts for number. (written for sed version of macOS, YMMV)

rmssh

#!/bin/bash

if [ -n "$1" ] #If input arg is non-empty then move on, but if it is prompt for number
then
	LINE="$1"
else
	echo "Enter line to delete of ~/.ssh/known_hosts:"
	read LINE
fi


re='^[0-9]+$'
if ! [[ $LINE =~ $re ]] ; then
   echo "Error: Enter a line number to delete" >&2; exit 1
fi

sed -i '' "$LINE"d ~/.ssh/known_hosts || exit 1