--- a/checker.py	Sat Jul 30 13:35:44 2016 +0800
+++ b/checker.py	Sat Jul 30 13:40:27 2016 +0800
@@ -91,13 +91,31 @@
     return ok
 
 
-def combined_env(lenv, penv):
-    if lenv and penv:
-        env = lenv.copy()
-        env.update(penv)
+def combined(a, b):
+    if a and b:
+        result = a.copy()
+        result.update(b)
     else:
-        env = lenv or penv
-    return env
+        result = a or b
+    return result
+
+
+def process_config(lc, pc):
+    c = {
+        'env': combined(lc.get('env'), pc.get('env')),
+        'vars': combined(lc.get('vars', {}), pc.get('vars', {}))
+    }
+
+    def render(items):
+        return [item % c['vars'] for item in items]
+
+    for key in ('flags', 'post_flags'):
+        c[key] = render(lc.get(key, []) + pc.get(key, []))
+
+    c['setup'] = [render(steps) for steps in lc.get('setup', [])]
+    c['exec'] = render(lc['exec'])
+    c['version'] = render(lc['version'])
+    return c
 
 
 def git_clone(url, dest):
@@ -223,41 +241,51 @@
         if name not in distinct:
             distinct.append(name)
 
-    print('# C&O installing linters: {}'.format(' '.join(distinct)))
-
     linter_config = {}
-
-    for linter in linters:
-        name = linter['name']
+    for name in distinct:
         if name in linter_config:
             continue
 
         lc = read_linter_config(name)
-
         if lc is None:
             print("# C&O skipping '{}': no config".format(name))
             continue
-
         if 'exec' not in lc:
             print("# C&O skipping '{}': no 'exec' in config".format(name))
             continue
 
         linter_config[name] = lc
 
-        for item in lc.get('setup', []):
-            if not run(item):
-                return False
+    installing = [name for name in distinct if name in linter_config]
+    print('# C&O installing linters: {}'.format(' '.join(installing)))
+    installed = []
+    setup_cache = set()
+    for linter in linters:
+        name = linter['name']
+        if name not in linter_config:
+            continue
+
+        lc = process_config(linter_config[name], linter)
+
+        if 'setup' in lc and str(lc['setup']) not in setup_cache:
+            for item in lc['setup']:
+                if not run(item):
+                    return False
+            setup_cache.add(str(lc['setup']))
 
         if 'version' in lc:
-            env = combined_env(lc.get('env'), linter.get('env'))
-            if not run(lc['exec'] + lc['version'], env=env):
+            if not run(lc['exec'] + lc['version'], env=lc['env']):
                 return False
 
-    print('# C&O linters installed: {}'.format(' '.join(linter_config.keys())))
+        if name not in installed:
+            installed.append(name)
+
+    print('# C&O linters installed: {}'.format(' '.join(installed)))
 
     print('# C&O task: checks')
     for linter in linters:
-        if linter['name'] not in linter_config:
+        name = linter['name']
+        if name not in linter_config:
             continue
 
         if config['scm'] == 'git':
@@ -267,15 +295,12 @@
         if files is False:
             return False
 
-        lc = linter_config[linter['name']]
+        lc = process_config(linter_config[name], linter)
 
         for f in files:
-            cmd = lc['exec']
-            flags = lc.get('flags', []) + linter.get('flags', [])
-            pf = lc.get('post_flags', []) + linter.get('post_flags', [])
+            cmd = lc['exec'] + lc['flags'] + [f] + lc['post_flags']
             codes = lc.get('codes', (1,))
-            env = combined_env(lc.get('env'), linter.get('env'))
-            if not run(cmd + flags + [f] + pf, ignore_codes=codes, env=env):
+            if not run(cmd, ignore_codes=codes, env=lc['env']):
                 return False
 
     return True