Using Crontab in a Python Script

Question

I am trying to use the contents of a crontab inside a python script. I want to do everything using python. In the end I hope to take the contents of the crontab, convert it to a temporary textfile, read in the lines of the text file and manipulate it.

Is there any way i can use the contents of the crontab file and manipulate it as if it were a text file???

I've looked into the subprocess module but am not too sure if this is the right solution....

NOTE: I am not trying to edit the crontab in any way, I am just trying to read it in and manipulate it within my python code. In the end, the crontab will remain the same. I just need the information contained inside the crontab to mess with.

What have you tried so far? The answers to this question list some Python packages you might be able to use to parse a crontab. — cxw
– cxw, Commented Jul 25, 2016 at 13:44

Wayne Werner · Accepted Answer · 2016-07-25 13:43:47Z

2

If you were to try crontab -h, which is usually the help option, you'll get this:

$ crontab -h
crontab: invalid option -- 'h'
crontab: usage error: unrecognized option
Usage:
 crontab [options] file
 crontab [options]
 crontab -n [hostname]

Options:
 -u <user>  define user
 -e         edit user's crontab
 -l         list user's crontab
 -r         delete user's crontab
 -i         prompt before deleting
 -n <host>  set host in cluster to run users' crontabs
 -c         get host in cluster to run users' crontabs
 -x <mask>  enable debugging

Default operation is replace, per 1003.2

The line to note is the one that says -l list user's crontab. If you try that, you see that it lists out the contents of one's crontab file. Based on that, you can run the following:

import subprocess

crontab = subprocess.check_output(['crontab', '-l'])

And crontab will contain the contents of one's crontab. In Python3 it will return binary data so you'll need crontab = crontab.decode().

answered Jul 25, 2016 at 13:43

Wayne Werner

52.3k35 gold badges213 silver badges304 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Connor Meeks Over a year ago

this is very close to what i am searching for. Lets say instead of running the command "crontab -l" I wanted to run "crontab -u root -l" would i change the subprocess command to subprocess.check_output(['crontab', '-u', 'root' , '-l'])?

Connor Meeks Over a year ago

additionally, would crontab.decode() allow me to treat the crontab as if it were a textfile?

Mayank Diwedi · Accepted Answer · 2018-04-18 07:57:17Z

0

As you are trying to change the crontab entry (e.g.- deleting the completed tasks):

import os
import datetime
os.system("crontab -l > new")
read_file = open("new","r")
write_file = open("new_edit","w")
today= datetime.datetime.now()
current_date = today.day
current_month = today.month
for lines in read_file:
        if lines=="\n":
                pass
        else:
                sep = lines.split(" ")
                if (current_date < int(sep[2]) and current_month == int(sep[3])):
                        write_file.write(lines)
write_file.close()
os.system("sudo mv new_edit /var/spool/cron/ec2-user")

This code will help to delete the previous day tasks. I think this will help you.

answered Apr 18, 2018 at 7:57

Mayank Diwedi

2111 gold badge3 silver badges7 bronze badges

Collectives™ on Stack Overflow

Using Crontab in a Python Script

2 Answers 2

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related