Change your Mac's screen resolution from the command line.

screenres.swift

#!/usr/bin/swift

// fix build errors with Swift 5. 
// Known issues: some resolution is not HiDPI

import Foundation

var shouldPrintUsage = true
var shouldPrintModes = true
var shouldSwitchMode = false
var didSwitchMode = false
var desiredDisplayNumber: Int? = nil
var desiredWidth: Int? = nil
var desiredHeight: Int? = nil
var desiredRefreshRate: Double? = nil

if CommandLine.arguments.count > 1 {
	desiredDisplayNumber = Int(CommandLine.arguments[1])
}
if CommandLine.arguments.count > 2 {
	desiredWidth = Int(CommandLine.arguments[2])
	shouldSwitchMode = true
	shouldPrintUsage = false
	shouldPrintModes = false
}
if CommandLine.arguments.count > 3 {
	desiredHeight = Int(CommandLine.arguments[3])
}
if CommandLine.arguments.count > 4 {
	desiredRefreshRate = Double(CommandLine.arguments[4])
}

if shouldPrintUsage {
	print("Usage: \(CommandLine.arguments[0]) [<displayNumber> <width>] [<height>] [<refreshRate>]")
	print("If no arguments are specified, then a list of available modes for each display will be printed.")
	print("If you specify a displayNumber and width (and optionally height and refreshRate) then that display will switch to the first mode that matches the values you specified.")
	print("After switching to a new mode, press Enter to quit the program and revert back to the default display mode.")
}

func isDesirableMode(displayNumber: Int, mode: CGDisplayMode) -> Bool
{
	if !shouldSwitchMode { return false }
	
	let height = mode.height
	let width = mode.width
	let refreshRate = mode.refreshRate
	
	if (desiredWidth == nil || width == desiredWidth) {
		if (desiredHeight == nil || height == desiredHeight) {
			if (desiredRefreshRate == nil || refreshRate == desiredRefreshRate) {
				return true
			}
		}
	}
	return false
}

let MAX_DISPLAYS : UInt32 = 32

var displays: [CGDirectDisplayID] = []
for _ in 0 ..< Int(MAX_DISPLAYS) { displays.append(0) }

var numDisplays: UInt32 = 0

CGGetActiveDisplayList (MAX_DISPLAYS, &displays, &numDisplays)

if numDisplays == 0 {
	print("ERROR: No displays found")
	exit(1)
}

for displayNumber in 0 ..< Int(numDisplays)
{
	if shouldPrintModes {
		print("Display: \(displayNumber)")
	}
	guard let modeArray = CGDisplayCopyAllDisplayModes (displays[displayNumber], nil) as [AnyObject]? else {
		print("ERROR: CGDisplayCopyAllDisplayModes returned nil")
		exit(2)
	}
	let count = CFArrayGetCount (modeArray as CFArray)
	if count == 0 {
		print("WARNING: Display \(displayNumber) has no modes.")
	}
	for modeNumber in 0 ..< count
	{
		let mode = modeArray[modeNumber] as! CGDisplayMode
		
		if shouldPrintModes {
			print("  \(mode.width) x \(mode.height) @ \(mode.refreshRate) Hz")
		}
		
		if (isDesirableMode(displayNumber: displayNumber, mode: mode)) {
			CGDisplaySetDisplayMode (displays[displayNumber], mode, nil)
			didSwitchMode = true
			break
		}
	}
}

if didSwitchMode {
	print("Press Enter to revert back to the default display mode.")
	_ = readLine()
}