Shell scripting: Iterate over a list line-by-line instead of word-by-word

Let’s say a directory contains these files:

My First File.txt
My Second File.txt

If you wanted to take an action on each distinct file, you might try something like this:

for file in `ls ~`; do echo $file; done

The output will look like below, because the spaces and line breaks are both treated delineators of a new item in the list (ie. a new assignment to the “file” variable.)

My 
First
File.txt
My
Second
File.txt

If your intent was to act on the complete filename (using only line breaks as indicators of a new item) then you can instead pipe your output through a “while” loop like this:

ls ~ | while read item; do echo $item; done

Which will yield the desired output:

My First File.txt
My Second File.txt

Monitoring Apple Caching Server Status via MunkiReport

Occasionally the Caching service on macOS will stop working due to a network outage or a glitch on Apple’s end.

It’s a simple enough fix — all you have to do is turn the service off and on again. But how do you know that it’s offline? It’s easy if you use MunkiReport with the Caching module enabled.

Just save the code below as a script on your MunkiReport database server and set it up as an hourly cron job. It looks for caching activity reported in the last two hours, and kicks off an alert if no results are found. (Be sure to read the notes below.)

#!/bin/bash

cachingactivity=`/bin/mysql munkireport -e "select \
collectiondate from caching where collectiondate > \
timestampadd(hour, +6, now()) order by \
collectiondate desc;"`;

if [[ $cachingactivity == "" ]]; then
     echo "Caching service may be offline."
fi

Considerations:

  • The user who runs the script needs to have a MySQL credential stored in their .my.cnf file.
  • Make sure cron is able to send you alerts. (Working MTA, and MAILTO=”user@domain” appears before this job is listed.)
  • You may need to modify the timezone offset (+6) to something suitable for your location. I’m at UTC-8, so +6 means my script looks for caching server activity reported within the last two hours.
  • Depending on how many clients there are, and whether any of them are on 24/7, you may need to adjust how far back your cron job is looking for records to avoid false error reports. Or only schedule it to check weekdays but not weekends.
  • Obviously this doesn’t provide up-to-the-minute alerting, but it should still help you notice if something is wrong before anyone else does.
  • With multiple caching servers, one could go down and you would not be alerted. The true purpose of this script is make sure that the caching service is working somewhere. It’s not concerned about calling out individual servers.

Munki, Monolithic Imaging, and Microsoft Office 2016 Volume License Serializer

If you have Macs that were cloned from an already-activated system (either via monolithic imaging, or one-off machines that were migrated or experienced hardware failure) you will find that your Office 2016 activation is broken. You will also find that Munki doesn’t know it needs to re-run the Office 2016 serializer since a receipt already exists for it.

I was able to work around this by adding a couple scripts to the serializer’s pkgsinfo. First I added an installcheck_script that looks for a file in /Users/Shared which contains the serial of the computer on which Office was activated. If it doesn’t match the computer’s serial, or if it doesn’t exist, then the serializer package will run. Then we use a postinstall_script to write the serial number of the current computer to this file so we know it’s been activated on this machine and doesn’t need to run again.

installcheck_script:

#!/bin/bash

machineserial=`system_profiler SPHardwareDataType | awk '/Serial/ {print $4}'`

activatedserial=`cat /Users/Shared/.office2016activatedserial`

if [[ $machineserial == $activatedserial ]]; then

exit 1

fi

postinstall_script:

#!/bin/bash

system_profiler SPHardwareDataType | awk '/Serial/ {print $4}' > /Users/Shared/.office2016activatedserial

Deploying Epson EasyMP Multi PC Projection for Mac

When adding Epson EasyMP Multi PC Projection 2.1.0 to Munki, I found that the built-in postinstall script fails.

Some digging revealed that the script was expecting a file to exist at </tmp/mpp-72B3FDFF-9513-4CED-96C3-34881FC77AB8>. It reads that file and uses the value contained for the “ClientMode” preference in </Library/Preferences/com.epson.EasyMP_Multi_PC_Projection.Settings/mppsettings.xml>

On a successful install the the GUI, that preference is just the integer “0”. So I added the following preinstall script to my Munki pkgsinfo.

#!/bin/bash
echo "0" > /tmp/mpp-72B3FDFF-9513-4CED-96C3-34881FC77AB8

The postinstall script is appeased and EasyMP Multi PC Projection 2.1.0 installs successfully. No direct modification or repackaging necessary.

Using SSH Keys for Passwordless Authentication

SSH keys can provide an additional layer of security (if you also disable password authentication on the server), or they can simplify the process of connecting to remote servers. For our purposes we’re interested in the latter – connecting to the server without entering a password.

The basic idea is that you create a public/private key pair on your computer, then upload the public key to the remote server. When you connect to the remote server, your computer can use the private key to authenticate instead of entering your password.

First we’ll create the key:

ssh-keygen -f ~/.ssh/id_rsa -N ""

If a key already exists, you’ll be asked if you want to overwrite it. If this happens you can respond by pressing “n” (no) and continue to the next step.

Next we need to upload the key to the server. Replace “user” with your username, and “host” with the address of the SSH server.

ssh-copy-id -i ~/.ssh/id_rsa user@host

If it worked, you should now be able to SSH to the remote host without entering your password.

Desktop Picture Profile Creator

DesktopPictureProfileCreator is a simple bash script that generates mobileconfig profiles for managing the desktop picture on macOS computers.

Run the script followed by the path to the image you want to set as the desktop picture. For example “sh DesktopPictureProfileCreator.sh /Library/Desktop\ Pictures/Aqua\ Blue.jpg”. Whatever path you specify must exist in the same location on the computer(s) you intend to deploy it to.

The profile will be created on the desktop of whichever user runs the script. In the example above, the profile would appear at ~/Desktop/Desktop-Aqua-Blue-jpg.mobileconfig

For more info and to download, check out my mobileconfigs repository on GitHub.

Yosemite Captive Portal Fix

A number of Yosemite Macs are having problems with our organization’s Wi-Fi captive portal.

If you don’t first sign in via the window presented by Captive Network Assistant, the system appears to have zero network connectivity. You can’t ping anything, you can’t perform DNS lookups, etc. It’s as if the OS is actively blocking all attempted connectivity until it knows you have succeeded in authenticating.

Consequently, Browsers throw errors instead of presenting our captive portal page. This is a big problem, since in many cases the Captive Network Assistant app was previously disabled or deleted!

I found I could whitelist our network so that it lets applications try connecting even if the Captive Network Assistant has not yet been placated.

Just copy the command below, replacing NAMEOFNETWORK with the SSID of your captive portal network. A reboot may be necessary, but it may also be enough to simply switch Wi-Fi off and on again.

sudo /usr/libexec/PlistBuddy -c "Add ScrapingParameters:DisabledRealms:0 string @NAMEOFNETWORK" /Library/Preferences/SystemConfiguration/CaptiveNetworkSupport/Settings.plist

AirPrintProfileCreator

AirPrintProfileCreator is a simple bash script which aids you in creating mobileconfig profiles that enable iOS devices to print to a CUPS server.

Download and run the script on your server (“sudo sh AirPrintProfileCreator.sh”) and follow the prompts on screen. When the profile has been created, you can install it on your iOS device via Configurator, MDM, or just post it online or email it to yourself.

The script should work on any recent Mac or other *nix systems with CUPS installed, but I have only tested on OS X v 10.9. Your CUPS server must have a static/reserved IP.

For more info and to download, check out my mobileconfigs repository page on GitHub.