if no input, try again instead of adding... support fetching an "empty" md

ui/fixtures/cmd.basic.json

@@ -47,6 +47,12 @@
 	"exit": 1,
 	"stderr": "ERROR: file not found: 'newfile.txt'\n"
 },
+{
+	"title": "Test file with no tag, with --empty --json",
+	"cmd": [ "list", "--json", "--empty", "newfile.txt" ],
+	"exit": 0,
+	"stdout": "{}\n"
+},
 {
 	"title": "invalid tag",
 	"cmd": [ "modify", "+tag", "newfile.txt" ],

ui/medashare/cli.py

@@ -1305,16 +1305,18 @@ def cmd_interactive(options, persona, objstr, cache):
 
 		inp = sys.stdin.readline().strip()
 
-		if inp == '1':
+		if not inp:
+			continue
+		elif inp == '1':
 			idx = max(0, idx - 1)
 			continue
-		if inp == '2':
+		elif inp == '2':
 			idx = min(len(files) - 1, idx + 1)
 			continue
-		if inp == '3':
+		elif inp == '3':
 			files, idx = getnextfile(files, idx)
 			continue
-		if inp == '4':
+		elif inp == '4':
 			files = sorted(curfile.parent.iterdir())
 			try:
 				idx = files.index(curfile)
@@ -1322,7 +1324,7 @@ def cmd_interactive(options, persona, objstr, cache):
 				print('WARNING: File no longer present.')
 				idx = 0
 			continue
-		if inp == '5':
+		elif inp == '5':
 			files = [ pathlib.Path(x) for x in options.files ]
 			try:
 				idx = files.index(curfile)
@@ -1330,7 +1332,7 @@ def cmd_interactive(options, persona, objstr, cache):
 				print('WARNING: File not present.')
 				idx = 0
 			continue
-		if inp == '6':
+		elif inp == '6':
 			print('Tag?')
 			try:
 				tag, value = sys.stdin.readline().strip().split('=', 1)
@@ -1345,11 +1347,11 @@ def cmd_interactive(options, persona, objstr, cache):
 				objstr.loadobj(metadata)
 
 			continue
-		if inp == '7':
+		elif inp == '7':
 			subprocess.run(('open', curfile))
 			continue
 
-		if inp.lower() == 'q':
+		elif inp.lower() == 'q':
 			break
 
 		try:
@@ -1421,6 +1423,10 @@ def cmd_list(options, persona, objstr, cache):
 
 				objs = objstr.by_file(i)
 			except (FileNotFoundError, KeyError) as e:
+				if options.empty and options.json:
+					print('{}')
+					continue
+
 				print('ERROR: file not found: %s' % repr(i), file=sys.stderr)
 				exit = 1
 				continue
@@ -1815,6 +1821,8 @@ def main():
 	parser_list = subparsers.add_parser('list', help='list tags on file(s)')
 	parser_list.add_argument('--json', action='store_true',
 	    help='output data as series of JSON objects')
+	parser_list.add_argument('--empty', action='store_true',
+	    help='output an empty JSON object if file not found or not metadata')
 	parser_list.add_argument('files', nargs='+',
 	    help='files to modify')
 	parser_list.set_defaults(func=cmd_list)