Python script won't start via bash

Question

I have this bash script that start the python script ms.py What is the problem here ?

#!/bin/bash
if [ $(ps aux | grep -e 'ms.py$' | grep -v grep | wc -l | tr -s "\n") -eq 0 ]; 
then python /root/folder/ms.py &
fi

and this in my crontab

*/1 * * * * /root/folder/script.sh

When I start the script manually it works normal.

I would make sure your cron user has the necessary programs in the PATH, starting with Python. Perhaps /full/path/to/python /root/folder/ms.py — sberry
– sberry, Commented Dec 28, 2013 at 17:45
What does your cron debug output says? By default it should email to root@localhost? — Mikko Ohtamaa
– Mikko Ohtamaa, Commented Dec 28, 2013 at 20:29

glenn jackman · Accepted Answer · 2013-12-28 23:18:50Z

1

you are testing the output of that pipeline against the number zero. I assume you want to start your python program only if it's not already running:

pid=$(pgrep -f 'ms.py$')
if [[ $pid ]] && kill -0 $pid; then
    echo already running
else
    echo not running
    python /root/folder/ms.py &
fi

answered Dec 28, 2013 at 23:18

glenn jackman

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2 Comments

nandhp Over a year ago

[[ $pid ]] should be [[ "$pid" ]]. The former won't work if pgrep doesn't match -- it will become [[ ]], which is a syntax error.

glenn jackman Over a year ago

@nandhp, not in bash: the double brackets are smart enough to avoid that trap: x=""; [[ $x ]] && echo y || echo n

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