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Change OS X network location based on the Wi-Fi network name

You might have heard about Network locations in OS X. It allows you to have different network configurations and quickly switch between them. For instance, if you must to use a corporate proxy server at work and you don’t need it when you get back home, you might create a new location named “Work” (with any necessary network proxy settings) and keep the default “Automatic” location for home. But still, you will need to switch between those locations manually. How annoying!

Wouldn’t it be great if OS X could switch location automatically based on the name of Wi-Fi network that I’m connected to? Moreover, I would like to change automatically some Security Preferences, because I have to lock the computer immediately at work when I go away. But I found it annoying to have it at home.

So, how to change automatically OS X’s network location based on the name of Wi-Fi network or run arbitrary scrips when it happens? Pretty easy! We will be following a convention over configuration paradigm to reduce the overall complexity.

First of all, we have to name locations after Wi-Fi network names. For instance, if the name of your corporate wireless network is “Corp Wi-Fi”, you have to create a new location “Corp Wi-Fi”. If you connect to a wireless network that you don’t have a specific location for, then the default location “Automatic” will be used.

And of course we need a tool for doing that. The installation process is extremely easy:

$ curl -L https://github.com/eprev/locationchanger/raw/master/locationchanger.sh | bash

It will ask only for a root password to install locationchanger. Now, every time you connect to a wireless network it will change the location to either the corresponding or the default one.

That’s not all. We still want to change Security Preferences automatically when the location has been changed. Let’s create scripts that will be executed every time it happens. One is for “Corp Wi-Fi” location:

#!/usr/bin/env bash

# Require password immediately after sleep or screen saver
osascript -e 'tell application "System Events" to set require password to wake of security preferences to true'

Another is for the default location:

#!/usr/bin/env bash

# Don’t require password after sleep or screen saver
osascript -e 'tell application "System Events" to set require password to wake of security preferences to false'

Save them as ~/.locations/Corp Wi-Fi and ~/.locations/Automatic respectively. Voilà! You’re not limited by changing only the security preferences, you can do whatever you want to…

Converting PNG to SVG

Let’s say, you’ve found a funny black-and-white picture on the Internet and you want it badly in hi-res or vector which is even better. Well, there is a command-line tool called Potrace.

Installation

It has precompiled distributions for OS X, Linux and Windows. Potrace is also available in major package managers, including Homebrew:

$ brew install potrace

The manual installation is super easy, however. For OS X do the following:

$ cd potrace-1.12.mac-i386
$ sudo cp mkbitmap.1 potrace.1 /usr/share/man/
$ sudp cp mkbitmap potrace /usr/local/bin

Usage

Potrace works with bitmaps (PBM, PGM, PPM, or BMP format). It means you have to convert the image you have to one of those formats. We will be using ImageMagick’s convert program. If you don’t have it installed, you can use Homebrew to get it:

$ brew install imagemagick

Alright. Let’s say you’ve got this image (by Nation of Amanda) in PNG format with transparency: ‘Nap all day, sleep all night, party never’ by Nation of Amanda All you need to do is to run this:

$ convert -alpha remove party-never.png pgm: \
| mkbitmap -f 32 -t 0.4 - -o - \
| potrace --svg -o party-never.svg

It converts PNG file to PGM format, removes image transparency, outputs the result image to the standard input of mkbitmap that transforms the input with highpass filtering and thresholding into a suitable for the potrace program format, that finally generates SVG file. You can play around with highpass filtering (-f) and thresholding (-t) values until you have the final look that you want.

As a result you might have now: ‘Nap all day, sleep all night, party never’ by Nation of Amanda That’s it.

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