Thursday, July 31, 2008

crontab to english translator

A couple of years ago I have written this script, that takes crontab entries from standard input, parses them and prints english translation. It is definitely not perfect and will bail at a lot of valid crontab entries, but for all it is worth here it is.


import re
import os
import sys
import string

class CronJob:
"""A class describing a scheduled job."""
def __init__(self, str):
Generate a new object from a crontab line. We should differentiate between the following types of crontabs:
1. something = something (raise exception)
2. (classic cron shedule)
3. [!&]word(arg)[,word(arg)...] (fcron style schedule)
4. #somestuff (comment, raise exception)
5. (empty line, raise exception)

if re.compile("^\s*$").search(str):
raise NotACronJobError("EMPTY")
elif re.compile("^\s*#").search(str):
m = re.compile("^\s*#(.*)").search(str)
raise NotACronJobError("COMMENT",
elif re.compile("^\s*\S+\s*=.+").search(str):
m = re.compile("^\s*(\S+?)\s*=\s*(.+)").search(str)
raise NotACronJobError("VARIABLE",,
elif re.compile("^(\*|\d+)").search(str) or re.compile("^[!&]\w+").search(str):
if re.compile("^!.+?\)\s*$").search(str): raise NotACronJobError("GARBAGE", str)
raise(NotACronJobError("GARBAGE", str))

def _parseLine(self, str):
if re.compile("^[!&]\w+").search(str):
self.type = "fcron"
m = re.compile("^\S+\s+(\S+)\s+(\S+)\s+(\S+)\s+(\S+)\s+(\S+)\s+(.+)").search(str)
self.type = "vixie"
m = re.compile("^(\S+)\s+(\S+)\s+(\S+)\s+(\S+)\s+(\S+)\s+(.+)").search(str)
self.min = self._parseDateTime(, "min") = self._parseDateTime(, "hr")
self.dom = self._parseDateTime(, "dom")
self.mon = self._parseDateTime(, "mon")
self.dow = self._parseDateTime(, "dow")
self.cmd = self._parseCmd(

def _parseDateTime(self, dt, type):
min = range(0,59)
hr = range(0,23)
dom = range(1,31)
mon = range(1,12)
dow = range(0-7)
if dt == "*":
return None
elif re.compile("^\d+$").search(dt):
return range(int(dt),int(dt) + 1)
elif re.compile(",").search(dt):
dts = dt.split(",")
parsed = [self._parseDateTime(x, type) for x in dts]
res = []
for x in parsed:
if res == None: res = []
res = res.extend(x)
return res
elif re.compile("\/").search(dt):
m = re.compile("(.+?)/(.+)").search(dt)
r =
st =
if r == "*":
r = eval(type)
(x,y) = r.split("-")
r = range(int(x),int(y))
return range(r[0], r[-1], int(st))
elif re.compile("-").search(dt):
m = re.compile("(\d+)-(\d+)").search(dt)
return range(int(,int(
raise NotACronJobError("GARBAGE", dt)

def _parseCmd(self, cmd):
if re.compile("^\s*root\s*").search(cmd):
cmd = re.compile("^\s*root\s*").sub("", cmd)
return cmd

def __str__(self):
s = "Run %s" % self.cmd
if self.mon != None:
months = ("Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec")
s = s + " in " + ",".join([months[x] for x in self.mon])
if self.dom != None:
tmp = ",".join(["%sth" % x for x in self.dom])
tmp = tmp.replace("1th", "1st")
tmp = tmp.replace("2th", "2nd")
tmp = tmp.replace("3th", "3rd")
s = s + " on " + tmp + " day"
if self.mon == None:
s = s + " of every month"
if self.dow != None:
week = ("sunday", "monday", "tuesday", "wednesday", "thirsday", "friday", "saturday")
s = s + " on " + ",".join([week[x] for x in self.dow])
if != None:
if len( == 1 and len(self.min) == 1:
s = s + " at %s:%s" % (string.zfill([0],2),string.zfill(self.min[0],2))
s = s + " at " + ",".join([str(x) for x in])
if self.dow == None and self.dom == None:
s = s + " every day"
s = s + " at %s minutes" % ",".join([str(x) for x in self.min]) + " of every hour "
return s

class NotACronJobError(Exception):
"""An exception raised by CronJob to indicate that the line in question doesn't contain a vaild cron schedule information."""
def __str__(self):
if self.args[0] == "EMPTY":
return "Empty Line"
elif self.args[0] == "COMMENT":
return "A comment: %s" % self.args[1]
elif self.args[0] == "VARIABLE":
return "An environment variable: %s = %s" % (self.args[1], self.args[2])
elif self.args[0] == "GARBAGE":
return "Uncronish thingamabob: %s" % self.args[1]
return "If you don't know how to play with me, go to the other sandbox!"

if __name__ == "__main__":
for line in sys.stdin:
print CronJob(line)
except NotACronJobError, err:
print err


  1. Thursday is spelt incorrectly, and it doesn't seem to parse this correctly:

    0 7 * * 2-5 echo hello

    Run echo hello on tuesday,wednesday,thirsday at 07:30

    I believe it should also cover friday (5)

  2. I made a try to do something similar in javascript. Cron translator:

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