#N/A: Add gem unknown command rule

README.md

@@ -164,6 +164,7 @@ using the matched rule and runs it. Rules enabled by default are as follows:
 * `fab_command_not_found` – fix misspelled fabric commands;
 * `fix_alt_space` – replaces Alt+Space with Space character;
 * `fix_file` – opens a file with an error in your `$EDITOR`;
+* `gem_unknown_command` – fixes wrong `gem` commands;
 * `git_add` – fixes *"pathspec 'foo' did not match any file(s) known to git."*;
 * `git_bisect_usage` – fixes `git bisect strt`, `git bisect goood`, `git bisect rset`, etc. when bisecting;
 * `git_branch_delete` – changes `git branch -d` to `git branch -D`;

tests/rules/test_gem_unknown_command.py

@@ -0,0 +1,82 @@
+import pytest
+from six import BytesIO
+from thefuck.rules.gem_unknown_command import match, get_new_command
+from tests.utils import Command
+
+stderr = '''
+ERROR:  While executing gem ... (Gem::CommandLineError)
+    Unknown command {}
+'''
+
+gem_help_commands_stdout = b'''
+GEM commands are:
+
+    build             Build a gem from a gemspec
+    cert              Manage RubyGems certificates and signing settings
+    check             Check a gem repository for added or missing files
+    cleanup           Clean up old versions of installed gems
+    contents          Display the contents of the installed gems
+    dependency        Show the dependencies of an installed gem
+    environment       Display information about the RubyGems environment
+    fetch             Download a gem and place it in the current directory
+    generate_index    Generates the index files for a gem server directory
+    help              Provide help on the 'gem' command
+    install           Install a gem into the local repository
+    list              Display local gems whose name matches REGEXP
+    lock              Generate a lockdown list of gems
+    mirror            Mirror all gem files (requires rubygems-mirror)
+    open              Open gem sources in editor
+    outdated          Display all gems that need updates
+    owner             Manage gem owners of a gem on the push server
+    pristine          Restores installed gems to pristine condition from files
+                      located in the gem cache
+    push              Push a gem up to the gem server
+    query             Query gem information in local or remote repositories
+    rdoc              Generates RDoc for pre-installed gems
+    search            Display remote gems whose name matches REGEXP
+    server            Documentation and gem repository HTTP server
+    sources           Manage the sources and cache file RubyGems uses to search
+                      for gems
+    specification     Display gem specification (in yaml)
+    stale             List gems along with access times
+    uninstall         Uninstall gems from the local repository
+    unpack            Unpack an installed gem to the current directory
+    update            Update installed gems to the latest version
+    which             Find the location of a library file you can require
+    yank              Remove a pushed gem from the index
+
+For help on a particular command, use 'gem help COMMAND'.
+
+Commands may be abbreviated, so long as they are unambiguous.
+e.g. 'gem i rake' is short for 'gem install rake'.
+
+'''
+
+
+@pytest.fixture(autouse=True)
+def gem_help_commands(mocker):
+    patch = mocker.patch('subprocess.Popen')
+    patch.return_value.stdout = BytesIO(gem_help_commands_stdout)
+    return patch
+
+
+@pytest.mark.parametrize('script, command', [
+    ('gem isntall jekyll', 'isntall'),
+    ('gem last --local', 'last')])
+def test_match(script, command):
+    assert match(Command(script, stderr=stderr.format(command)))
+
+
+@pytest.mark.parametrize('script, stderr', [
+    ('gem install jekyll', ''),
+    ('git log', stderr.format('log'))])
+def test_not_match(script, stderr):
+    assert not match(Command(script, stderr=stderr))
+
+
+@pytest.mark.parametrize('script, stderr, result', [
+    ('gem isntall jekyll', stderr.format('isntall'), 'gem install jekyll'),
+    ('gem last --local', stderr.format('last'), 'gem list --local')])
+def test_get_new_command(script, stderr, result):
+    new_command = get_new_command(Command(script, stderr=stderr))
+    assert new_command[0] == result

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)