Prevent unnecessary writes and the -m option

Author: dvershinin

README.md

@@ -96,20 +96,36 @@ pip install sde
 
 ## Notes
 
+### Quoting in JSON
+
 Quoting is avoided for `null`, `true`, `false`, and numeric values.
 To ensure that a given value is quoted, use `-s` (or `--string`) option:
 
 ```bash
 sde -s key null file.json
 ```
 
+### Force-fail on missing keys
+
 If you must *edit* the file, by ensuring to update only the existing key, use `-e` (`--must-exist`)
 option. The program will exit without adding the key which doesn't exist.
 
 ```bash
 sde -e key val file.json
 ```
 
+### Force-fail on unchanged file
+
+If the data is unchanged after running `sde` (values already match), you can force
+a failure exit code `2` by passing the `-m` option:
+
+```bash
+sde -m key sameval file.json
+# > exit code 0
+sde -m key sameval file.json
+# > exit code 2
+```
+
 ## TODO
 
 ### Work with stdin

sde/__about__.py

@@ -1 +1 @@
-__version__ = '1.1.8'
+__version__ = '1.1.9'

sde/sde.py

@@ -24,15 +24,17 @@
 
 def edit_file(key, value, file, fmt, must_exist=False):
     data = DottedDict(read_file(file, fmt))
-    if must_exist:
-        try:
-            # this is the way I found it works for array vals too
-            # e.g. fruits.0.name
-            data[key]
-        except KeyError:
+    try:
+        # this is the way I found it works for array vals too
+        # e.g. fruits.0.name
+        if data[key] == value and type(data[key]) == type(value):
+            # prevents writing to the file is value is matching already
+            return False
+    except KeyError:
+        if must_exist:
             raise ValueError('{} is not present in {}'.format(key, file))
     data[key] = value
-    write_file(file, fmt, data)
+    return write_file(file, fmt, data)
 
 
 def read_file(file, fmt):
@@ -60,6 +62,7 @@ def write_file(file, fmt, data):
             fd.write(to())
             fd.close()
             os.rename(tmp, file)
+            return True
         except Exception:
             # We can assume we can remove it, because we successfully created
             # it with O_EXCL above.
@@ -103,11 +106,13 @@ def main():
     parser.add_argument('file', metavar='<filename>', help='Filename to edit')
     parser.add_argument('-e', '--must-exist', dest='must_exist', action='store_true',
                         help='Throw error and exit if the key does not already exist')
+    parser.add_argument('-m', '--must-change', dest='must_change', action='store_true',
+                        help='Exit with status code 2 if the values already match and file unchanged')
     parser.add_argument('-s', '--string', dest='is_string', action='store_true',
                         help='Always treat value as a string by quoting it')
     parser.add_argument('--version', action='version',
                         version='%(prog)s {version}'.format(version=__version__))
-    parser.set_defaults(is_string=False, must_exist=False)
+    parser.set_defaults(is_string=False, must_exist=False, must_change=False)
     args = parser.parse_args()
 
     if args.is_string:
@@ -123,7 +128,9 @@ def main():
         sys.exit(1)
 
     try:
-        edit_file(args.key, val, args.file, fmt, must_exist=args.must_exist)
+        res = edit_file(args.key, val, args.file, fmt, must_exist=args.must_exist)
+        if args.must_change and res is False:
+            sys.exit(2)
     except ValueError as e:
         print("\033[91mError: \033[0m" + str(e), file=sys.stderr)
         sys.exit(1)