What's it all about, Alfie?

Surprising Fact: Cron Jobs aren’t in a Shell

Today I was surprised to learn that cron jobs are not run in a shell. That was really a surprise. The reason it shocked me was that I had the following in a crontab:

  15 05 * * mon-fri  $HOME/bin/startQL | $HOME/bin/campfire -p

where I'd written a nice little bash script to send a piped message to our Campfire room, and I wanted to pipe the output of the startQL command to that room so we'd be able to see what happened without having to check our email.

The script takes stdin and sends it on as a pass-through, but with a copy being send to Campfire. It's a pretty nice little script that just uses the Campfire curl API:

#!/bin/bash # # This script takes stdin and sends it to the QuantumLead Campfire room as # Canadarm. This can take an optional '-p' argument so that the stdin will # be treated as a "paste" and go in as a fix-edwidth font paste. Otherwise, # it'll appear as a simple proportional font "message" # # Let's make sure all the commands we need are accessible to us... export PATH="/usr/local/bin:/usr/local/sbin:/usr/sbin:/sbin:$HOME/bin:$PATH" # start with the AuthToken for Canadarm and the QuantumLead room token="969baac86c42c23ff715f0000000000000000000:X" room="511111" # see if we have the option to treat it as a 'paste' paste='' for arg in "$@"; do case "$arg" in -p) paste='<type>PasteMessage</type>' ;; esac done # grab all of stdin - unless there is nothing, and put in something body=$(cat) if [ ${#body} -eq 0 ]; then body='empty' fi # now we can build up the curl command and ship it out msg="<message><body>${body}</body>$paste</message>" url="https://thepoint.campfirenow.com/room/$room/speak.xml" ans=`curl -u "$token" -H 'Content-type: application/xml' -d "$msg" $url 2>/dev/null | grep 'starred type'` if [ ${#ans} -eq 0 ]; then echo 'Bad news - sending to campfire failed!' fi echo "${body}"

What I found was that the pipe wasn't working because we weren't in a real shell. It was easy enough to fix - just put the commands in a new file and call that, or use a subshell:

  15 05 * * mon-fri  ($HOME/bin/startQL | $HOME/bin/campfire -p)

Learn something new every day!

This entry was posted on Monday, October 8th, 2012 at 11:30 am and is filed under Coding, Cube Life. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

Surprising Fact: Cron Jobs aren’t in a Shell

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