Shell doesn't run python ONLY when executed by crontab

Question

I have a shell script which runs python then attaches a pdf to an email via mutt.

Shell script:

cd ./pod_reports/script/
whereareyou=`pwd`
OUT=`python3 dummy.py`
cd ..
filename=$(ls *.pdf -1t | head -1)
strt="echo Did we get python? "
mailmutt="| mutt -s 'Subject Line' -a $filename -- [email protected]"
stmt="$strt$whereareyou$OUT$mailmutt"
echo $stmt
eval $stmt

Python Script, dummy.py

import sys
OUT = sys.stdout.write(" I did python!! ")
sys.exit(0)

When the shell script is run directly from the command line, I get the expected pwd via 'wherareyou' and the 'I did python!!' statement in the email body, along with the expected attachment. When the script scheduled via crontab, I get the same expected 'whereareyou' and attachment, but I do not get the message from python. My understanding from this is that python is not getting run at all when the shell is executed by crontab.

I don't understand why. Is this somehow expected behavior from crontab? If so, how can a series of scripts be scheduled if not within a shell?

Answer 1

Answer: crontab may have different program paths than your command line.

As it so happens, in our system the 'mutt' (email) program was stored in /usr/bin/ and this path was known by whatever mechanism runs crontab and so it was successfully able to send emails. However, many programs I wanted to run in this shell, including python3, were located in a different directory: /usr/local/bin/. Programs in this local folder were not known by crontab (indeed, even running which python3 from within a shell scheduled by crontab would return nothing). This is despite both mutt and python3 working when I run a shell from my command line.

The solution is to run the programs of interest (in my case python3) from their absolute paths:

cd ./pod_reports/script/
whereareyou=`pwd`
OUT=`/usr/local/bin/python3 dummy.py`
cd ..
filename=$(ls *.pdf -1t | head -1)
strt="echo Did we get python? "
mailmutt="| mutt -s 'Subject Line' -a $filename -- [email protected]"
stmt="$strt$whereareyou$OUT$mailmutt"
echo $stmt
eval $stmt