MacOS – Launch daemon not processing program arguments

The Program key specifies the file to execute, & the ProgramArguments key specifies the arguments which will be passed to the executing process. Strictly speaking you can pass whatever arguments you want to a process, but the convention is that the first one should be the name by which the process was invoked, so most programs ignore their first argument.^‡ The file to execute is obviously necessary information, but if the Program key is is missing, launchd pretends it has the same value as the first argument in ProgramArguments purely as a convenience.

Your first example starts boinccmd & gives it arguments that would be equivalent to the terminal command

--host\ localhost --passwd\ gobbledygook --project\ http://setiathome.berkeley.edu/\ update

which tells boinccmd that you invoked it as "--host localhost" & only passed it two weird arguments.

Your second example separates the arguments correctly, but as Eddie Kelley suggested it needs one inserted at the front. It tells boinccmd that you invoked it as "--host", then passed another six arguments. boinccmd can recognise the last five as being two options, but has no idea what the "localhost" business is about. As far as boinccmd can tell, it was invoked from the terminal as

/Library/Application\ Support/BOINC\ Data/boinccmd localhost --passwd gobbledygook --project http://setiathome.berkeley.edu/ update

(note the missing "--host").

boinccmd is probably one of the great majority of programs that don't care what their first argument is, so you could probably actually just shove <string>HELLO</string> at the head of the ProgramArguments array, but it's probably cleaner to remove the Program key altogether & just use this:

<key>ProgramArguments</key>
    <array>
        <string>/Library/Application Support/BOINC Data/boinccmd</string>
        <string>--host</string>
        <string>localhost</string>
        <string>--passwd</string>
        <string>gobbledygook</string>
        <string>--project</string>
        <string>http://setiathome.berkeley.edu/</string>
        <string>update</string>
    </array>

^‡ It can seem like a meaningless redundancy, but some programs use this to good effect: bash et al. act as login shells if their first argument begins with -, & Vim enters various emulation modes if its first argument is ed or vi instead of vim.

The second launchd job ticket format is almost correct. Only a set of quotes need removing.

Quotes

The quotes are no longer needed in the second launchd job ticket, so change:

<string>"set volume output volume 0"</string>

…to…

<string>set volume output volume 0</string>

Grouping Arguments

In this case, the quotes grouped the set of arguments for osascript to see as one item. Thus osascript gets two arguments, the flag -e and the script. This meets the requirements from the osascript manual.

When called through Terminal.app and thus through the shell, the quotes are needed to perform the grouping. When osascript gets the arguments, the shell has removed the quotes.

Without quotes, spaces subdivide each item passed via the shell.

When called through a launchd job ticket, the grouping is intrinsic within the array passed as ProgramArguments. In your first ticket, the array contained nine items and in the second ticket, the array contained three.

LaunchAgent

Be sure to add this launchd job as a ~/Library/LaunchAgents as osascript requires an active user with a graphical session.

This approach approximates what I do with Power Manager in How to Set the Volume When Logging In.