ssh-dump

#!/bin/bash

set -eo pipefail
export LC_ALL=C

err=0
ssh_cmd=( /export terse )
suff_fmt='%Y-%m-%d_%H%M%S'
n=9
rm_empty=t

usage() {
	bin=$(basename $0)
	echo >&2 "Usage: $bin [-x] [-e] [-n N] [-s suffix-fmt] dst-file user@host [command...]"
	echo >&2
	echo >&2 "Run command on a remote host non-interactively, dumping output to dst-file."
	echo >&2
	echo >&2 "dst-file is rotated (N copies preserved) and can have compression-type suffix."
	echo >&2 "E.g. using backup.gz will use gzip to compress it, same with xz, lz4, zst."
	echo >&2 "Empty resulting files are silently dropped, unless -e option is specified."
	echo >&2 "Rotated files will have date/time suffix, use -n 0 to disable rotation entirely."
	echo >&2
	echo >&2 "Default command (if not specified): ${ssh_cmd[@]}"
	echo >&2 "Default rotation count (N, 0 - disable): $n"
	echo >&2 "Default date/time suffix format (used for alphanumeric sort): $suff_fmt"
	exit ${1:-0}
}

while getopts ":hn:s:xe" opt
do case "$opt" in
	h) usage 0 ;;
	n) [[ $OPTARG =~ ^[0-9]+$ ]] && n=$OPTARG \
		|| { echo >&2 -e "ERROR: Invalid -n value: $OPTARG\n"; usage 1; } ;;
	s) suff_fmt=$OPTARG ;;
	e) rm_empty= ;;
	x) set -x ;;
	*) { echo >&2 -e "ERROR: Invalid option: -$OPTARG\n"; usage 1; } ;;
esac; done
shift $((OPTIND-1))

[[ $# -ge 2 ]] || usage 1
file=$1 host=$2
shift; shift
[[ $# -le 0 ]] || ssh_cmd=( "$@" )

ssh_opts=(
	-nT -oControlPath=none -oControlMaster=no
	-oConnectTimeout=180 -oServerAliveInterval=6 -oServerAliveCountMax=10
	-oBatchMode=yes -oPasswordAuthentication=no -oNumberOfPasswordPrompts=0 )

[[ "${file%.tmp}" = "$file" ]] || { echo >&2 "ERROR: dst filename cannot end with .tmp"; exit 1; }
file_dst="$file.$(date +"$suff_fmt")" file_tmp="$file_dst".tmp
ssh "${ssh_opts[@]}" "$host" -- "${ssh_cmd[@]}" >"$file_tmp" \
	|| { rm -f "$file_tmp"; echo >&2 "ERROR: ssh dump command failed"; exit 1; }

[[ -n "$rm_empty" && ! -s "$file_tmp" ]] || {
	declare -A compress_opts=( [gz]=gzip [xz]=xz [lz4]=lz4 [zst]=zstd )
	compress=${compress_opts[${file##*.}]}
	if [[ -z "$compress" ]]
	then mv "$file_tmp" "$file_dst"
	else "$compress" <"$file_tmp" >"$file_dst" || { mv "$file_tmp" "$file_dst"
		echo >&2 "ERROR: failed to compress resulting dump-file using $compress"; err=1; }
	fi; }
rm -f "$file_tmp"

[[ $n -le 0 ]] || {
	readarray -t files < <(ls -1 "$file".* | sort)
	n_files=${#files[@]}
	for p in "${files[@]}"; do
		[[ $n_files -gt $n ]] || break
		rm -f "$p"
		[[ "${p%.tmp}" != "$p" ]] || (( n_files -= 1 ))
	done; }

exit $err