puressh 0.2.4

A pure-Rust SSH (Secure Shell) protocol library, in the spirit of libssh, built on purecrypto.
Documentation 
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#!/bin/sh
# ssh-copy-id — install public keys in a remote account's authorized_keys.
#
# usage: ssh-copy-id [-f] [-n] [-i [identity_file]] [-p port] [-F ssh_config]
#                    [-t target_path] [-o ssh_option] ... [user@]hostname
#
# puressh version of the OpenSSH helper: the keys are sent over ssh and the
# remote side appends only those not already present, creating ~/.ssh
# (0700) and authorized_keys (0600) as needed.
set -u

usage() {
	cat >&2 <<USAGE
Usage: $0 [-f] [-n] [-i [identity_file]] [-p port] [-F alternative ssh_config file] [-t target_path] [[-o <ssh -o options>] ...] [user@]hostname
	-f: force mode -- copy keys without checking which are already installed
	-n: dry run    -- no keys are actually copied
	-h|-?: print this help
USAGE
	exit 1
}

ID_FILE=
DRY_RUN=
TARGET_PATH=.ssh/authorized_keys
SSH=${SSH_COPY_ID_SSH:-ssh}
set --  "$@" --end--
OPTS=
while [ "$1" != --end-- ]; do
	case "$1" in
	-i)
		# -i without a file: the default identity.
		case "${2:-}" in
		-* | --end-- | '') ID_FILE=default ;;
		*) ID_FILE=$2; shift ;;
		esac
		;;
	-i*) ID_FILE=${1#-i} ;;
	-p | -F | -o) OPTS="$OPTS $1 $(printf %s "$2" | sed "s/'/'\\\\''/g; s/^/'/; s/\$/'/")"; shift ;;
	-p* | -F* | -o*) OPTS="$OPTS '$1'" ;;
	-t) TARGET_PATH=$2; shift ;;
	-f) ;; # remote de-duplication makes force mode the same as normal
	-n) DRY_RUN=1 ;;
	-s) ;; # always uses the shell path
	-x) set -x ;;
	-h | '-?') usage ;;
	--) shift; break ;;
	-*) echo "$0: unknown option $1" >&2; usage ;;
	*) set -- "$@" "$1" ;;
	esac
	shift
done
# Remaining positional argument(s) after --end-- are the host.
while [ "$1" != --end-- ]; do shift; done
shift
[ $# -eq 1 ] || usage
HOST=$1

if [ -z "$ID_FILE" ] && keys=$(ssh-add -L 2>/dev/null) && [ -n "$keys" ]; then
	KEYS=$keys
	FROM="the agent"
else
	if [ -z "$ID_FILE" ] || [ "$ID_FILE" = default ]; then
		ID_FILE=$(ls -t "$HOME"/.ssh/id_*.pub 2>/dev/null | head -n 1)
		[ -n "$ID_FILE" ] || { echo "$0: ERROR: No identities found" >&2; exit 1; }
	fi
	case "$ID_FILE" in *.pub) ;; *) [ -r "$ID_FILE.pub" ] && ID_FILE=$ID_FILE.pub ;; esac
	[ -r "$ID_FILE" ] || { echo "$0: ERROR: failed to open ID file '$ID_FILE'" >&2; exit 1; }
	KEYS=$(grep -v '^[[:space:]]*\(#\|$\)' "$ID_FILE")
	FROM="\"$ID_FILE\""
fi
printf '%s\n' "$0: INFO: Source of key(s) to be installed: $FROM" >&2

if [ -n "$DRY_RUN" ]; then
	printf '%s\n' "$KEYS" | sed 's/^/would add: /' >&2
	exit 0
fi

# Run with sh on the remote side whatever the login shell is.
REMOTE=$(cat <<'REMOTE'
umask 077
t="$1"
d=$(dirname "$t")
mkdir -p "$d" && touch "$t" || exit 1
n=0
while IFS= read -r k; do
	[ -n "$k" ] || continue
	grep -qxF "$k" "$t" && continue
	[ -z "$(tail -c1 "$t")" ] || echo >> "$t"
	printf '%s\n' "$k" >> "$t" || exit 1
	n=$((n + 1))
done
command -v restorecon >/dev/null 2>&1 && restorecon -F "$d" "$t" >/dev/null 2>&1
echo "$n"
REMOTE
)
quoted=$(printf %s "$REMOTE" | sed "s/'/'\\\\''/g")
target_q=$(printf %s "$TARGET_PATH" | sed "s/'/'\\\\''/g")
remote_cmd="exec sh -c '$quoted' sh '$target_q'"
# Rebuild the collected ssh options as arguments (they were quoted for this).
eval "set -- $OPTS"
# $SSH may carry its own options: split it on purpose.
# shellcheck disable=SC2086
added=$(printf '%s\n' "$KEYS" | $SSH "$@" -- "$HOST" "$remote_cmd") || {
	echo "$0: ERROR: failed to install the key(s)" >&2
	exit 1
}
echo
echo "Number of key(s) added: $added"
echo
echo "Now try logging into the machine, with: \"$SSH$OPTS '$HOST'\""
echo "and check to make sure that only the key(s) you wanted were added."
echo