validate datasets exist before running

- this allows for early exit as well as better error messaging

CHANGES.md

@@ -6,11 +6,18 @@ Not Yet Released
 
 (nothing yet)
 
+`v1.5.0`
+--------
+
+- Sanity check datasets existence before running
+ - `-q` will hide warnings for datesets not existing
+ - Based on ([#9](https://github.com/bahamas10/zfs-prune-snapshots/pull/9))
+
 `v1.4.1`
 --------
 
 - Allow snapshot datasets to contain spaces
-  ([#18](https://github.com/bahamas10/zfs-prune-snapshots/pull/18)
+  ([#18](https://github.com/bahamas10/zfs-prune-snapshots/pull/18))
 
 `v1.4.0`
 --------

zfs-prune-snapshots

@@ -69,7 +69,7 @@ EOF
 }
 
 debug() {
-	((verbosity >= 1)) && echo "$@" >&2
+	((verbosity >= 1)) && echo '>' "$@" >&2
 	return 0
 }
 
@@ -174,6 +174,7 @@ verbosity=0
 prefix=
 suffix=
 invert=false
+quiet=false
 while getopts 'hniqlRp:s:vV' option; do
 	case "$option" in
 		h) usage; exit 0;;
@@ -182,7 +183,7 @@ while getopts 'hniqlRp:s:vV' option; do
 		l) listonly=true;;
 		p) prefix=$OPTARG;;
 		s) suffix=$OPTARG;;
-		q) exec 1>/dev/null;;
+		q) quiet=true; exec 1>/dev/null;;
 		R) recursive=true;;
 		v) ((verbosity++));;
 		V) echo "$VERSION"; exit 0;;
@@ -221,13 +222,10 @@ fi
 
 shift
 
-pools=("$@")
 destroyargs=()
 code=0
 totalused=0
 numsnapshots=0
-humanpools=${pools[*]}
-humanpools=${humanpools:-<all>}
 
 if $recursive; then
 	destroyargs+=('-R')
@@ -243,6 +241,36 @@ if ! command -v zfs &>/dev/null; then
 	exit 1
 fi
 
+# validate pools given, print warnings if not in quiet mode
+pools=()
+for arg in "$@"; do
+	debug "checking '$arg' exists"
+
+	error=$(zfs list "$arg" 2>&1 1>/dev/null)
+	code=$?
+	debug "zfs list '$arg' -> exited $code"
+
+	if ((code == 0)) && [[ -z $error ]]; then
+		debug "adding dataset '$arg'"
+		pools+=("$arg")
+	else
+		msg="dataset '$arg' invalid: $error"
+		debug "$msg"
+		if ! $quiet; then
+			echo "$msg" >&2
+		fi
+	fi
+done
+
+# it is an error if arguments were given but all datasets were invalidated
+if [[ -n $1 && -z ${pools[0]} ]]; then
+	echo 'no valid dataset names provided' >&2
+	exit 1
+fi
+
+humanpools=${pools[*]}
+humanpools=${humanpools:-<all>}
+
 # first pass of the pools (to calculate totals and filter unwanted datasets
 lines=()
 while read -r line; do