Daemon Loop

Daemon loop is simple and clean CLI utility to run programs periodically.

It's better alternative to running commands like:

while true; do date >> date.log; sleep 5; done 

(or even running such commands in screen/tmux sessions)

Installation

pip3 install daemon-loop

Usage

usage: loop [-h] [-n N] [-p PERIOD] [--log FILENAME] [-e] [-v] [-d]
            command [command ...]

Run command in loop (with features)

positional arguments:
  command               command with arguments

optional arguments:
  -h, --help            show this help message and exit
  -n N                  Run N times and exit (default: 0 = infinite)
  -p PERIOD, --period PERIOD
                        Run every N seconds (default: 60)
  --log FILENAME        Write command stdout to this file
  -e, --err             Write command stderr to logfile)
  -v, --verbose         Write loop technical info to logfile)
  -d, --daemon          Work as daemon

Example usage

Simple and almost useless - run date every second until Ctrl-C:

$ loop date
Sun Dec 20 05:18:21 +07 2020
Sun Dec 20 05:19:21 +07 2020
Sun Dec 20 05:20:21 +07 2020
^C

Run date +%s (print unixtime) 3 times every 10 seconds and quit

$ loop -p 10 -n 3 -- date +%s
1608416485
1608416495
1608416505

And now something more useful - make our date program a daemon!

$ loop -dvep 10 --log /tmp/loop.log -- date +%s
$ pidof -x loop
25934

• -d: run as daemon
• -v: include technical info about time of start/stop, status code and daemon pid
• -e (--err): include stderr to logfile
• -p (--period): period is 10 seconds
• --log: logfile

log file will look like this:

# 2020-12-20 05:39:01 my pid: 25934 run: date +%s
1608417541
# 2020-12-20 05:39:01 finished with status 0

# 2020-12-20 05:39:11 my pid: 25934 run: date +%s
1608417551
# 2020-12-20 05:39:11 finished with status 0

Caveats

If --daemon used, loop will chdir to '/'. Loop will automatically adjust path to logfile and executable, but you should care about other parameters. For example, command loop -d -- touch myfile started from user home will touch /myfile (in root), and most likely will fail.