#!/bin/bash
# Works on all GNU systems and tested on MacOS 10.15.13
# Deletes certain lines of ~/.ssh/known_hosts
# Check if any args passed
if [ $# -eq 0 ]; then
    echo "Usage: ./delete_certain_known_hosts 3 5 7 23"
    echo "Will catch duplicate line numbers"
    exit 1
fi
# Set variables
known_hosts_path=~/.ssh/known_hosts
lines_in_known_hosts=$(wc -l "$known_hosts_path" | awk '{print $1}')
lines_to_delete=""
# Dedupe, sort numerically, and create array from args string
IFS=' '
deduped_args=$(echo "$@" | xargs -n1 | sort -nu | xargs)
read -r -a delete_these_lines <<< "$deduped_args"
# Loop through creating sed expression
for var in "${delete_these_lines[@]}"; do
if [[ "$var" -gt "$lines_in_known_hosts" ]]; then
  echo "$var is invalid line in $lines_in_known_hosts line $known_hosts_path"
else
  lines_to_delete+="${var}d;"
fi
done
# Output information to user about what happened
if [[ -z "$lines_to_delete" ]]; then
  echo "All arguments passed were invalid lines in $known_hosts_path"
else
  sed -i'' -e "$lines_to_delete" "$known_hosts_path"
  echo "Deleted lines $(echo $(echo "$lines_to_delete" | sed 's/d;/, /g') | sed 's/.$//' )"
fi