#N/A: Add gem unknown command rule

thefuck/rules/gem_unknown_command.py

@@ -0,0 +1,32 @@
+import re
+import subprocess
+from thefuck.utils import for_app, eager, replace_command
+
+
+@for_app('gem')
+def match(command):
+    return ('ERROR:  While executing gem ... (Gem::CommandLineError)'
+            in command.stderr
+            and 'Unknown command' in command.stderr)
+
+
+def _get_unknown_command(command):
+    return re.findall(r'Unknown command (.*)$', command.stderr)[0]
+
+
+@eager
+def _get_all_commands():
+    proc = subprocess.Popen(['gem', 'help', 'commands'],
+                            stdout=subprocess.PIPE)
+
+    for line in proc.stdout.readlines():
+        line = line.decode()
+
+        if line.startswith('    '):
+            yield line.strip().split(' ')[0]
+
+
+def get_new_command(command):
+    unknown_command = _get_unknown_command(command)
+    all_commands = _get_all_commands()
+    return replace_command(command, unknown_command, all_commands)