How to get arguments of NSRunningApplication?

Question

How do I get the list of arguments using during launch for a NSRunningApplication, similar to the ones I see when I run ps aux:

let workspace = NSWorkspace.shared
let applications = workspace.runningApplications

for application in applications {
    // how do I get arguments that were used during application launch?
}

Answer 1

The "ps" tool uses sysctl() with KERN_PROCARGS2 to get the arguments of a running process. The following is an attempt to translate the code from adv_cmds-153/ps/print.c to Swift. That file also contains a documentation of the memory layout of the raw argument space and explains how to locate the string arguments in that memory.

func processArguments(pid: pid_t) -> [String]? {
    
    // Determine space for arguments:
    var name : [CInt] = [ CTL_KERN, KERN_PROCARGS2, pid ]
    var length: size_t = 0
    if sysctl(&name, CUnsignedInt(name.count), nil, &length, nil, 0) == -1 {
        return nil
    }
    
    // Get raw arguments:
    var buffer = [CChar](repeating: 0, count: length)
    if sysctl(&name, CUnsignedInt(name.count), &buffer, &length, nil, 0) == -1 {
        return nil
    }
    
    // There should be at least the space for the argument count:
    var argc : CInt = 0
    if length < MemoryLayout.size(ofValue: argc) {
        return nil
    }
    
    var argv: [String] = []
    
    buffer.withUnsafeBufferPointer { bp in
        
        // Get argc:
        memcpy(&argc, bp.baseAddress, MemoryLayout.size(ofValue: argc))
        var pos = MemoryLayout.size(ofValue: argc)
        
        // Skip the saved exec_path.
        while pos < bp.count && bp[pos] != 0 {
            pos += 1
        }
        if pos == bp.count {
            return
        }
        
        // Skip trailing '\0' characters.
        while pos < bp.count && bp[pos] == 0 {
            pos += 1
        }
        if pos == bp.count {
            return
        }
        
        // Iterate through the '\0'-terminated strings.
        for _ in 0..<argc {
            let start = bp.baseAddress! + pos
            while pos < bp.count && bp[pos] != 0 {
                pos += 1
            }
            if pos == bp.count {
                return
            }
            argv.append(String(cString: start))
            pos += 1
        }
    }
    
    return argv.count == argc ? argv : nil
}

There is only a simple error handling: if anything goes wrong, the function returns nil.

For an instance of NSRunningApplication you can then call

processArguments(pid: application.processIdentifier)