crontab.py

#!/usr/bin/python

##############################################################################
#  copyright Vincent Lemoine, credits to Emilio Schapira
#
#  This program is free software; you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation; either version 2 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software
#  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
#  MA 02110-1301, USA.
#
##############################################################################

##############################################################################
#
# 	usage: 	python crontab.py [crontab.txt]
#
#			this program can be used in Windows to schedule task specified
#			in crontab.txt. The program is simular to the linux cron utility
#
#           All files are supposed to be in the sam directory
#
##############################################################################

import datetime
import os
import signal
import sys
import tempfile
import time

filetime = 0

cwd = f"{os.getcwd()}"      # get current working directory


def deltasleep(t=60):    	# due to crontab startup delay, starttime is synced up to t seconds
    sec = float(datetime.datetime.now().strftime("%S.%f"))  # get seconds.microseconds
    delta = 0.0          	# init delta
    r = sec % t          	# calculate remainder
    delta = t - r        	# calculate time diff in seconds so 0 <= delta <= t
    return float(delta)  	# return delta as sleep time


def log(msg):				# print msg and log msg logfile
    f = open(logFileName, 'a')
    f.write(time.ctime(time.time()) + " cron: " + msg + "\n")
    print(time.ctime(time.time()) + " cron: " + msg)
    f.close()


def signal_handler(signal, frame):  # handle keyboard signals and quit
    print('You pressed Ctrl+C!')
    sys.exit(0)


def run(command):
    try:
        # For windows prepend "start" to spawn the shell command in another process and avoid waiting
        startprefix = ''
        if os.name == 'nt':
            startprefix = 'start '
            ext = command.split()[0][-5:-1]
            if ext in ('.bat', '.cmd'):
                startprefix += 'cmd /C '

        cmd = startprefix+command
        log(cmd)
        os.system(cmd)
    except:
        log('last command failed to start')


def match(value, expr, interval=1):

    # print "value="+str(value)+"; expr="+str(expr)+"; interval="+str(interval)

    if expr == '*':					# return 1 when expr="*"
        return 1

    values = expr.split('-')       # expr like n-m
    if len(values) > 1:				# return 1 for every value in interval n-m
        try:
            if value >= int(values[0]) and value <= int(values[1]):
                return 1
        except:
            pass

    values = expr.split('/')		# expr like */n
    if len(values) > 1:				# return 1 for every n occurence
        if int(interval) != 0:
            try:
                if int(value) % int(values[1]) == 0:
                    # print "/ 1"
                    return 1
            except:
                pass

    values = expr.split(',')		# expr like n,m,o,p
    for v in values:
        try:
            if int(v) == value:
                return 1
        except:
            pass

    return 0


def CheckCrontabUpdate(crontabFileName):

    # whenever crontabFileName has been changed a new internal $crontab.bin is generated
    #	- replace symbolic names (@daily, @mon, etc)
    #	- remove comment and empty lines

    global filetime

    try:
        # os.stat(filename) get file attributes
        mtime = int(os.stat(crontabFileName).st_mtime)
    except:
        log(f"error reading config file, crontab = {crontabFileName}")
        sys.exit(4)

    if filetime != mtime:  # check if modified time has been changed

        filetime = mtime

        try:
            lines = open(crontabFileName, 'r').readlines()  # Read the crontab file

            # replace special keywords by standard syntax before processing
            lines = [keywords.replace('@year', '0 0 1 1 *') for keywords in lines]
            lines = [keywords.replace('@daily', '0 0 * * *') for keywords in lines]
            lines = [keywords.replace('@midnight', '0 0 * * *') for keywords in lines]
            lines = [keywords.replace('@noon', '0 12 * * *') for keywords in lines]
            lines = [keywords.replace('@hourly', '0 * * * *') for keywords in lines]
            lines = [keywords.replace('@monthly', '0 0 1 * *') for keywords in lines]
            lines = [keywords.replace('@weekly', '0 0 * * 0') for keywords in lines]
            lines = [keywords.replace('@mon', '0 0 * * 0') for keywords in lines]
            lines = [keywords.replace('@tue', '0 0 * * 1') for keywords in lines]
            lines = [keywords.replace('@wed', '0 0 * * 2') for keywords in lines]
            lines = [keywords.replace('@thu', '0 0 * * 3') for keywords in lines]
            lines = [keywords.replace('@fri', '0 0 * * 4') for keywords in lines]
            lines = [keywords.replace('@sat', '0 0 * * 5') for keywords in lines]
            lines = [keywords.replace('@sun', '0 0 * * 6') for keywords in lines]
            lines = [keywords.replace('@reboot', '#reboot') for keywords in lines]  # ignore reboot

            log("generating internal crobtab: %s" % crontabGenerated)
            cron = open(crontabGenerated, 'w')
            for line in lines:
                if line[0] != '#' and len(line.strip()) != 0:
                    cron.write(line)
            cron.close()

        except:  # issue error message when crontab cannot be opened
            log('error opening %s file' % crontabFileName)


# init #############################################################################

signal.signal(signal.SIGINT, signal_handler)  # setup signal handler

tmpdir = tempfile.gettempdir()  # get the current temporary directory

if os.name == 'nt':
    tmpdir = tmpdir+"\\"
else:
    tmpdir = tmpdir+"/"

# default file names, pid and log file to temp dir
crontabFileName = f"{cwd}/crontab.txt"
logFileName = tmpdir+"crontab.log"
pidFileName = tmpdir+"crontab.pid"
crontabGenerated = f"{cwd}/$crontab.bin"
#print(tmpdir, crontabFileName, logFileName, pidFileName, crontabGenerated)

try:  # override defaults with arguments
    crontabFileName = sys.argv[1]
except:
    pass

# Write the pid in the current directory.
f = open(pidFileName, 'w')
f.write(str(os.getpid()))
f.close()

# Log cron start
log('Python version %s.%s.%s' % sys.version_info[:3])
log('started with file %s' % crontabFileName)
log('wait %s seconds for first crontab scan' % round(deltasleep(60), 2))

# wait to next minute (hh:mm:00)
# time.sleep(deltasleep(60))

# start here #############################################################################

while 1:  # loop forever

    #log('scanning for tasks to be executed')
    time.sleep(1)				# to be sure we passed the minute (hh:mm:01)

    # generated new internal $crontab.bin if crontab.txt has been changed
    CheckCrontabUpdate(crontabFileName)

    curTime = time.localtime()  # get current localtime

    # 	format curTime : time.struct_time(tm_year=2016, tm_mon=11, tm_mday=10, tm_hour=12, tm_min=11, tm_sec=4, tm_wday=3, tm_yday=315, tm_isdst=0)
    #
    #	0	=	year	(tm_year)	year
    #	1	=	month	(tm_mon)	(1,...,12)
    #	2	=	day		(tm_mday)	(0,...,28[,29[,30[,31]]])
    #	3	=	hour	(tm_hour)	(0,...,23)
    #	4	=	minute	(tm_min)	(0,...,59)
    #	5	=	second	(tm_sec)	(0,...,59)
    #	6	=	weekday	(tm_wday)	(0,...,6)	(0=Mon,...,6=Sun)
    #	7	=	ytd		(tm_yday)	day of year (1,...,365[,366])
    #	8	=	dst		(tm_isdst)	daylight saving time [0|1]
    #

    try:
        lines = open(crontabGenerated, 'r').readlines()  # Read the generated $crontab.bin file
        lineNum = 1										# line numbering

        for line in lines:								# process every line in lines
            if line[0] != '#' and len(line.strip()) != 0:  # Ignore comments and empty lines
                try:
                    tokens = line.split()
                    #print(line, tokens)
                    # See if the cron entry matches the current time minute
                    cronMatch = match(curTime[4], tokens[0])
                    # See if the cron entry matches the current time hour
                    cronMatch = cronMatch and match(curTime[3], tokens[1])
                    # See if the cron entry matches the current day
                    cronMatch = cronMatch and match(curTime[2], tokens[2])
                    # See if the cron entry matches the current month
                    cronMatch = cronMatch and match(curTime[1], tokens[3])
                    # See if the cron entry matches the current weekday (in crontab 0=Monday,...,6=Sunday)
                    cronMatch = cronMatch and match(curTime[6], tokens[4], 0)

                    if cronMatch:  # if true fire command
                        cmd = " ".join(tokens[5:])
                        #print(tokens, cmd)
                        run(cmd)

                except:  # issue error message when crontab contains errors
                    log('error parsing line %i of %s' % (lineNum, crontabGenerated))

            lineNum = lineNum + 1

    except:  # issue an error message when crontab cannot be opened
        log('error opening %s file' % crontabGenerated)

    time.sleep(deltasleep(60))  # wait 60 seconds, until next minute