Tech Reflect

If you use the defaults command to set preferences, it’s easy to forget that you ever did. Some implications of this:

• You could be filling up your drive with logs or slowing your system down
• You could run into other bugs later that are caused by the default itself
• An update to an app might not benefit you because the default you set is overriding behavior

Finding defaults

The defaults command has a find subcommand, but I’ve found that people generally aren’t aware of it. Let’s say you set some defaults relating to your trackpad, but don’t know what domain they are in:

defaults find trackpad

Found 3 keys in domain 'Apple Global Domain': {
     "com.apple.trackpad.forceClick" = 0;
     "com.apple.trackpad.scaling" = 3;
     "com.apple.trackpad.scrolling" = "0.75";
 }
 Found 3 keys in domain 'com.apple.AppleMultitouchTrackpad': {
     Clicking = 0;
     DragLock = 0;
     

… READ THE REST

One of the (few) nice things about a shell script is that if you share it with someone, they can look at the source code and see how it works or modify it for their own purposes.

It’s not as quick and dirty as a bash script, for example, but it has some big advantages:

• It’s Swift and it’s a great way to learn it and reduce the number of languages you need to know
• You can use Xcode to create the tool and have the full power of Xcode debugging
• Writing tools in bash can be very frustrating due to the unusual syntax and lack of some modern language features.

There’s one downside though. The output from Xcode is a compiled binary, so people have to check out your source code from a repository to see how it works. So, here’s what you can do after you’ve created your … READ THE REST

Rather than write a script for something you may only need once, there’s an easy way to repeat a series of command-line commands. This works in bash and may in other shells:

while [ 1 ]; do <some command>; <some other command>; sleep <some delay in seconds>; done;

So, for example:

while [ 1 ]; do date; uptime; sleep 10; done;

This will generate:
Mon Mar 19 13:20:30 PDT 2018
13:20 up 1:23, 3 users, load averages: 3.25 3.87 3.51
Mon Mar 19 13:20:40 PDT 2018
13:20 up 1:24, 3 users, load averages: 3.31 3.86 3.51
Mon Mar 19 13:20:50 PDT 2018
13:20 up 1:24, 3 users, load averages: 5.44 4.30 3.67

Just use Ctrl-C to end.

Extra credit

Add a counter so that it runs 10 times only:

for n in $(seq 1 10); do date; uptime; sleep 10; done

It seems like whenever I want to write an if-then or case statement in bash, I spent an hour searching the web and end up finding 12 different suggested ways of doing it. I try them all and maybe one of them works if I’m lucky.

I happened to find what I think is a really great reference for this that has been a great resource for me:

Bash Scripting Tutorial – 5. If Statements

Things like string comparisons, inspecting files, boolean operations, and nested flow control are some of the topics covered. Sure, there is the official bash documentation mentions this stuff, but it’s very terse and doesn’t provide good examples, if at all.

Having said all this, I highly recommend writing command-line tools in Swift:

Creating command-line tool in Swift

Not only will you be increasing your knowledge of Swift, it’s much more powerful, more easily debuggable, … READ THE REST

Shell aliases are woefully underused. Painfully, I frequently see people do the following:

• Type a shell command with the same 4 arguments cd into the same folders
• ssh into the same machines or devices
• Run the same sequence of commands

Aliases are super easy. Just open your ~/.bashrc file (or equivalent) and start adding them. I’ll now give a bunch of examples I use.

“ls” command

I have many variations I use on the “ls” command. I don’t even remember what the arguments mean anymore because I’ve been using these shortcuts for so long.

# default arguments I like
alias l='ls -AG' 

# Long listing
alias ll='ls -aAlGh'

# Do a grep afterwards (My most often used)
alias lg='ls -AlGOh@ | grep -i '

# Newest files at bottom (My second most often used)
alias lt='ls -AltrGhu' 

# Largest files at bottom
alias lz='ls -AlGrhS' 

# Extended attributes

… READ THE REST

If you’ve ever had a bizarre problem in Xcode and you’ve given up hope, this post is for you. Some frustrating things you might see:

• Breakpoints stop working
• A framework or library can’t be found that the compiler found moments ago
• Symbols in linked frameworks are no longer found
• This is not a comprehensive list.

I wrote this script a decade ago and in this frustrating moments, I run it, and go get a refreshing beverage while my computer reboots. It’s kind of unbelievable how often this has saved me. Maybe it will help you at least once in your life.

Note: Read the script first as it deletes your caches and DerivedData folder. It shouldn’t be a problem but you should be aware what it’s doing.

#!/bin/zsh

rm -rf ~/Library/Developer/Xcode/DerivedData 

#edit this to point to your DerivedData folder
rm -rf ~/Library/Caches/*Xcode*

sudo find /var/folders -iname xcode -exec mv \{\} 

… READ THE REST

It’s fairly straightforward to leverage launchd to run a script either at specified intervals or at specific times of the day. I find that most people only want to do fairly simple things, so I’ve kept this simple.

The way launchd works is that you create a plist, then run a command to either load or unload the plist. Here is an example plist that will run the script called “rsync-backup-work” every 3 hours. The first 3 lines are just boilerplate for a plist.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN"
     "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
     <key>Label</key>
          <string>org.cricket.rsync-backup-work</string
     <key>ProgramArguments</key>
          <array>
               <string>/Users/admin/bin/rsync-backup-work</string
          </array>
     <key>StartInterval</key>
          <integer>10800</integer>
</dict>
</plist>

This has only three keys:

• Label → Unique identifier (this can just be the name of the plist without the plist suffix to make it simple)
• ProgramArguments → First item in the array is the path to an executable, the rest would be

… READ THE REST

If you use multiple Macs, you may find yourself writing and editing scripts that could be useful on all of your machines. This is another potential use of iCloud Drive. Here’s what I do:

• I created a “bin” folder at the top level of my iCloud Drive
• I set up a symlink from my home directory to iCloud Drive on each of my machines using the same iCloud account:

ln -s /Users/admin/Library/Mobile\ Documents/com~apple~CloudDocs/bin ~/bin 

• I set up my shell config file to add ~/bin to the PATH variable.

export PATH=~/bin:/usr/bin:/bin:$PATH

• Start writing and editing scripts that are quickly available on all machines!

Related posts:

Many-to-many screensharing
Sharing shell settings between Macs
Multiple Macs, one location for screenshots

Multiple Macs, one location for screenshots

Sharing scripts between machines
Many-to-many screensharing
Sharing shell settings between Macs
Multiple Macs, one location for screenshots