diff --git a/cmdutils.py b/cmdutils.py
new file mode 100644
index 0000000..6590286
--- /dev/null
+++ b/cmdutils.py
@@ -0,0 +1,95 @@
+'''
+call external tools to do things.
+'''
+
+import os
+import re
+import subprocess
+from functools import lru_cache
+from collections import namedtuple
+from typing import List
+
+@lru_cache(maxsize=20)
+def lookupip(ip, cmd='cip'):
+  return subprocess.getoutput(subprocess.list2cmdline([cmd, ip])).replace('CZ88.NET', '').strip() or '-'
+
+def check_mediafile(file):
+  '''intergrity check with ffmpeg
+
+  also return ``False`` when reading the file fails
+
+  From http://superuser.com/a/100290/40869
+  '''
+
+  p = subprocess.Popen(
+    ['ffmpeg', '-v', 'error', '-i', file, '-f', 'null', '-'],
+    stderr = subprocess.PIPE)
+  _, e = p.communicate()
+  return not bool(e.strip())
+
+PingResult = namedtuple('PingResult', 'loss avg mdev')
+
+def ping(host, *, count=4):
+  p = subprocess.Popen(
+    ['ping', '-c', str(count), host],
+    stdout = subprocess.PIPE)
+  out, _ = p.communicate()
+  out = out.decode()
+  _, loss, stat, _ = out.rsplit('\n', 3)
+  loss = re.findall(r'\d+(?=%)', loss)[0]
+  loss = float(loss) / 100
+  if stat:
+    stat = stat.split()[3]
+    _, avg, _, mdev = stat.split('/')
+  else:
+    avg = mdev = -1
+  return PingResult(loss, float(avg), float(mdev))
+
+def get_directory_size(d):
+  return int(subprocess.check_output(
+    ['du', '-sb', d]).decode().split(None, 1)[0])
+
+def get_entropy(input):
+  if isinstance(input, bytes):
+    stdin = subprocess.PIPE
+    data = input
+  else:
+    stdin = input
+    data = None
+  p = subprocess.Popen(
+    ['ent', '-t'],
+    stdin = stdin,
+    stdout = subprocess.PIPE,
+  )
+  out = p.communicate(data)[0].decode()
+  header, data = out.splitlines()
+  header = header.split(',')[1:]
+  data = [float(x) for x in data.split(',')[1:]]
+  data[0] = int(data[0])
+  return {h: d for h, d in zip(header, data)}
+
+def so_depends(sopath: os.PathLike) -> List[str]:
+  env = os.environ.copy()
+  env['LANG'] = env['LC_ALL'] = 'C'
+  out = subprocess.check_output(
+    ['objdump', '-p', sopath],
+    env=env, encoding='utf-8')
+
+  libs = []
+
+  for line in out.splitlines():
+    line = line.strip()
+    if line.startswith('NEEDED '):
+      libs.append(line.split(None, 1)[-1])
+
+  return libs
+
+def diff_text(a, b):
+  import tempfile
+  with tempfile.NamedTemporaryFile(mode='w') as af, \
+      tempfile.NamedTemporaryFile(mode='w') as bf:
+    af.write(a)
+    af.flush()
+    bf.write(b)
+    bf.flush()
+    subprocess.run(['git', 'diff', '--', af.name, bf.name])