Convert shell history or CLI args into ~/.ssh/config format.

ssh2config.sh

#!/bin/bash

ssh2append() {
  ssh -G "$@" | sed -n 's/^hostname /Host /p'
  comm -23 <(ssh -G "$@" 2>/dev/null | sort) <(ssh -G . 2>/dev/null | sort) | sed 's/^/    /'
  
  # This loop+if is for remote command, -N, -W as -G lacks support
  while getopts '1246AaCfGgKkMNnqsTtVvXxYyB:b:c:D:E:e:F:I:i:J:L:l:m:O:o:p:Q:R:S:W:w:' opt; do
    #shellcheck disable=SC2254
    case "$opt" in
      4|6|A|a|C|f|G|g|K|k|M|n|q|s|T|t|X|x|v|Y|y) ;;
      B|b|c|D|E|e|F|I|i|J|L|l|m|O|o|p|R|S|w) ;;
      N) echo "    remotecommand exec sleep infinity" ;;
      W) echo "    remotecommand nc ${OPTARG/:/ }" ;;
      *) echo "Unsupported flag -$opt" >2; exit 1 ;; #12QV
    esac
  done
  shift "$OPTIND"
  [[ "$#" -eq 0 ]] || printf '%q ' remotecommand "$@" | sed 's/^/    /; s/ $/\n/'

  echo ''
}

if [[ "$#" -eq 0 ]]; then
  eval "$(sed -n 's/^: [0-9]*:[0-9]*;//; /-G/d; /--help/d; s/^ssh /ssh2append /p;' \
      ~/.*sh_history | sort -u)"
else
  ssh2append "$@"
fi