launchd plist character substitution

Question

I have LaunchAgent plist file that contains the following Program Arguments

<key>ProgramArguments</key>
    <array>
        <string>/Applications/UniFi.app/Contents/PlugIns/jre1.8.0_121.jre/Contents/Home/jre/bin/java</string>
        <string>-Djava.awt.headless=true</string>
        <string>-Xmx1024M</string>
        <string>-jar</string>
        <string>/Applications/UniFi.app/Contents/Resources/lib/ace.jar</string>
        <string>start</string>
    </array>

The initial path to the embedded java distribution (int this case version jre1.8.0_121.jre) changes when the people from Ubiquiti update their application, but the installed that they provide does not include the LaunchAgent modification, so I have to do it by hand every time.

I tried to put something like

<string>/Applications/UniFi.app/Contents/PlugIns/jre*.jre/Contents/Home/jre/bin/java</string>

… but as I have read here there is no substitution inside the plist file.

Any ideas on how to achieve this? This way the plist file can stay the same regardless the updated version of the embedded distribution.

Thank you you all

Answer 1

I haven't tested it, but you should be able to add <EnableGlobbing><true/> to the plist file, and use the wildcard. From the launchd.plist man page:

EnableGlobbing <boolean>

This flag causes launchd to use the glob(3) mechanism to update the program arguments before invocation.

Since this doesn't seem to be working, another possibility that occurred to me is to run a shell, and let it to the wildcard expansion. You could create a short script, and have launchd run that, or just use bash -c:

<key>ProgramArguments</key>
    <array>
        <string>/bin/bash</string>
        <string>-c</string>
        <string>exec /Applications/UniFi.app/Contents/PlugIns/jre*.jre/Contents/Home/jre/bin/java -Djava.awt.headless=true -Xmx1024M -jar /Applications/UniFi.app/Contents/Resources/lib/ace.jar start</string>
    </array>

Note that since it's being passed to a shell via -c, the entire command (including arguments) must be passed as a single long argument separated by spaces rather than as separate arguments. Also, I added exec so the shell will replace itself with the java executable rather than hanging out as a (useless) parent process.