Macos – Ruby commands are turning off tty echo

There's no way to step through a script to see how it would execute without actually doing that. In your example, there are no if statements or loops. But in real scripts, there are often lots of conditional statements. Which branch will get taken will often depend on what happened when the shell ran the previous command. If it doesn't run the command, there's no way for the shell to know what output it would have generated or what the return code would have been, which the next conditional branch or assignment statement might depend on.

If the point is that you'd like to scrutinize a script and know what it does before you run it, that's not a bad idea. But realistically, about the best way to do that is by just browsing the file with less or vi or something similar.

Added

If you're developing a script and you're wanting to step through it the first time, testing the logic but not actually doing any damage if you've got a bug, the solution I'm often able to use is to modify only the statements that could do any damage by pasting an echo onto the front.

This often works in typical real-life scripts because (a) generating the lists of items you'll iterate over or the value to which you'll set a variable can often be generated without changing the filesystem and (b) it's usually sufficient to assume that if you did run the command, it would succeed.

http://www.cultofmac.com/176329/turn-off-internal-lcd-display-of-your-macbook-air-os-x-tips/

You can try these, Tip 1 has worked for me however you must close the lid during start-up/reboot before the logo appears. Once the login screen appears you can open the lid and the screen should be off. Can check with the brightness control buttons.

This is not an ideal solution as closing/opening the lid every time can be quite bothersome but it works (more info below). An option from Apple to turn this off with external monitors connected would be ideal.

Link: http://gizmodo.com/5938452/a-trick-to-make-using-an-external-monitor-with-your-macbook-way-better

Here is a terminal command thats fairly simple that will allow you to keep the lid open for adequate cooling but while using the external display only. I've been using this method with my Thunderbolt display and MacBook Air since the beta of Mountain Lion came out and it works perfect. Has all the same characteristics of good old clamshell mode. Be sure to keep this written down someplace in the off chance you need to re-install, do a PRAM reset, or just want to undo it.

To execute in Terminal:

sudo nvram boot-args="iog=0x0"

To undo in Terminal:

sudo nvram -d boot-args

Once you type it into terminal I believe you need to enter your password. I then restart my machine. Now the TRICK is to either restart your machine with the lid already closed (hit restart then slam the lid!) OR turn the machine on for the first time (then quickly slam the lid!) once you are past the login screen you can open the lid.

ALSO: if the machine is asleep, and you simply forget and open the lid, it will wake up both displays. So just remember to wake the machine up with an external bluetooth mouse or keyboard.