Script inside launchd plist

Question

Hi,
playing with lauchd plists to get some feeling about how certain things works I came up with this script inside the plist
<key>ProgramArguments</key>
<array>
<string>/bin/sh</string>
<string>-c</string>
<string>/bin/df -k| /usr/bin/grep /dev/ | /usr/bin/awk '{ OFS="     "; "date +%d-%b-%Y-%I:%M| getline; print $6, $1, $4, $5;}'</string>
</array>
Its close to what I try to do in my trial stage one (1), but see some unwanted and unexpected issues
1. why is there a tab at the first line?
2. Where is the first Item, is it replaced with the date or just ignored?
3. Should I see the result(s) of date as a multi word? If I keep a space between +%d-%b-%Y and %I:%M i get a wrong result.
*this is what I get*
29-May-2010-10:53
/Volumes/TimeMachine /dev/disk5s3 303667180 69%
/Volumes/RAID01 /dev/disk4 55598552 93%
/Volumes/Repository /dev/disk0s3 96066032 2%
/Volumes/Data /dev/disk0s4 506853520 40%
/Volumes/Applications /dev/disk1s4 11657776 73%
*This what I actually did expect with the current script ( not what I want );*
29-May-2010-10:53 / /dev/disk1s3 16190024 62%
29-May-2010-10:53 /Volumes/TimeMachine /dev/disk5s3 303667180 69%
29-May-2010-10:53 /Volumes/RAID01 /dev/disk4 55598552 93%
29-May-2010-10:53 /Volumes/Repository /dev/disk0s3 96066032 2%
29-May-2010-10:53 /Volumes/Data /dev/disk0s4 506853520 40%
29-May-2010-10:53 /Volumes/Applications /dev/disk1s4 11657776 73%
I thought that the date line will get printed every time for each line from the previous piped command
*This is what I want ( stage 1 )*
29-May-2010 10:53
/ /dev/disk1s3 16190024 62%
/Volumes/TimeMachine /dev/disk5s3 303667180 69%
/Volumes/RAID01 /dev/disk4 55598552 93%
/Volumes/Repository /dev/disk0s3 96066032 2%
/Volumes/Data /dev/disk0s4 506853520 40%
/Volumes/Applications /dev/disk 1s4 11657776 73%
*This is what I finally want ( stage 2 )*
29-May-2010 10:53
/ 1s3 16190024 62%
TimeMachine 5s3 303667180 69%
RAID01 4 55598552 93%
Repository 0s3 96066032 2%
Data 0s4 506853520 40%
Applications 1s4 11657776 73%
Any help or ideas are welcome.
Thanks
PS.
Here the total launchd plist script for copy>test ( check output path )
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Debug</key>
<true/>
<key>InitGroups</key>
<false/>
<key>Label</key>
<string>net.test.PlayWithMeScript2</string>
<key>LowPriorityIO</key>
<true/>
<key>ProgramArguments</key>
<array>
<string>/bin/sh</string>
<string>-c</string>
<string>/bin/df -k| /usr/bin/grep /dev/ | /usr/bin/awk '{ OFS="     "; "date+%d-%b-%Y-%I:%M"| getline; print $6, $1, $4, $5;}'</string>
</array>
<key>RunAtLoad</key>
<true/>
<key>ServiceDescription</key>
<string>Play With me script</string>
<key>StandardOutPath</key>
<string>/Volumes/TestBedDevelopment/TestLogs/log3.txt</string>
<key>StartInterval</key>
<integer>60</integer>
<key>WorkingDirectory</key>
<string>/</string>
</dict>
</plist>

Answer 1

Absolutely true, but to learn the effects of the shell created by the launchd and a comment somewhere on the web about "if it can in launchd do it there" and that I dont want to install to much, I choose for this, for now.
Then, with all due respect to whoever wrote that article, he's an idiot
Launchd has many uses, but it's not the right place to put a multi-step script with umpteen pipes and dependencies.
Besides, I'm actually surprised it even remotely works, since launchd normally requires each element in the command to be in a separate <ProgramArguments> array element. In other words, your original:
<key>ProgramArguments</key>
<array>
<string>/bin/sh</string>
<string>-c</string>
<string>/bin/df -k| /usr/bin/grep /dev/ | /usr/bin/awk '{ OFS="\t"; "date+%d-%b-%Y-%I:%M"| getline; print $6, $1, $4, $5;}'</string>
</array>
should really be more like:
<key>ProgramArguments</key>
<array>
<string>/bin/sh</string>
<string>-c</string>
<string>/bin/df</string>
<string>-k</string>
<string>|</string>
<string>/usr/bin/grep</string>
<string>/dev/</string>
<string>|</string>
<string>/usr/bin/awk</string>
<string>'{</string>
<string>OFS="\t";</string>
<string>"date+%d-%b-%Y-%I:%M"</string>
<string>|</string>
<string>getline;</string>
<string>print</string>
<string>$6,</string>
<string>$1,</string>
<string>$4,</string>
<string>$5;}'</string>
</array>
and now you can see why it's a really, really bad idea to do. Far easier to just:
<key>ProgramArguments</key>
<array>
<string>/usr/local/bin/myscript.sh</string>
</array>
and put all the logic in a separate file.
The first line is gone because you're using getline within your awk statement, which tells awk to skip to the next line.
I did hoped that didn't effect everything after the ;
No. As per man awk:
The ``function'' getline sets $0 to the next input record from the current input file;
so getline moves onto the next line.
How can I return a value from a launchd?
What do you mean 'return a value from launchd'? You don't normally interact with launchd, so getting a return value from it doesn't make much sense.
And why does my script keep running?
because that's what launchd is for. By default, launchd is tasked with launching a process and keeping it running. So if a process fails it automatically gets restarted. This is normally what you want for system-level processes.
Now, that said, launchd has a number of variations that you can use to tell it to launch processes at specific times, or when certain events happen, or only at boot time, etc., but you need to add them to your .plist so that launchd knows when (and when not) to launch/restart your process.