The Robservatory

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Unix

View app-specific log messages in Terminal

It’s not often I get to use a tweet by Many Tricks own Peter Maurer as the inspiration for a tip. But this tip is such a case, as he recently complained about Console and its inability to see old output. A response from @fzwob taught me something I didn’t know:

That command browses the captured macOS log data and pulls out anything that matches the specified process name. This could be useful if you’re having troubles with an app and wonder if anything was logged relative to your troubles. Or you might be asked to send the log data if you’re working with the developer on your issue.

Unfortunately, the quotes and dashes in the command as tweeted have been prettified (by Twitter?); here it is in raw Terminal form, using our own Moom as an example:

log show --predicate 'processImagePath CONTAINS[c] "Moom"'

When you press Return, the command will start digging into the log file, and soon start spewing output—possibly a lot of output—to your screen.

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Edit long Terminal commands in a visual editor

Here’s a quickie tip for those of us who occasionally string together complex commands at Terminal’s prompt: You may want to add this simple line to your .profile (or whatever init file you use):

set -o vi

What does it do? It tells Unix/Terminal to set the input line editor to vi. When might this be useful? Let’s say you’ve typed a long command, like the one to launch a background screen saver:

/System/Library/Frameworks/ScreenSaver.framework/Resources/ScreenSaverEngine.app/Contents/MacOS/ScreenSaverEngine -module "Arabesque" -background &

Before you hit Return, you notice a couple of typos early in the command. You could use cursor movement keys to move around, of course, but with the above command in place, just press Escape and hit v: The entered command will open for editing in vi. Make your changes, then do the usual :wq vi exit dance, and your edited command will then execute.

Note that if you edit a command but then don’t save it (i.e. you press :q!, you may have to hit Return on the command line to get out of an odd “waiting for v to edit” mode. (At least that’s the only way I found to return to normal typing.)

Open Unix man pages in their own Terminal window

A while back, I wrote about opening Unix man pages in Preview, and this is still my preferred method of browsing man pages. However, there may be times where Preview is overkill, and you want to stay in Terminal, maybe for a short help file such as that for ln. But opening a new window by hand is a bit of a pain, and tabs won’t work because you can’t see both the window and the man page at the same time.

While browsing the old Mac OS X Hints site, I found this nice solution: Open man pages in a new Terminal window, one that’s set up just for reading such pages. It looks something like this (though I’ve customized my setup; keep reading)…

Adding a few lines to your shell’s startup file makes opening these ‘in their own window’ man pages as easy as opening ‘regular’ man pages.

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The little I know about regex…and where to learn more

First off, regex is shorthand for a regular expression. And what, exactly, is a regular expression? According to the linked Wikipedia page, a regular expression is…

…in theoretical computer science and formal language theory, a sequence of characters that define a search pattern. Usually this pattern is then used by string searching algorithms for “find” or “find and replace” operations on strings.

That’s a mouthful, but what it means is that you can write some really bizarre looking code that will transform text from one form to another form. And if you know just a bit of regex, and where to go to look up what you don’t know, then you can use regex to do many useful things.

For example, consider this filename on a scanned-to-PDF receipt:

The Party Place [party supplies] - 02-06-2017

Perhaps you’d prefer it if the date came first, in year-month-day order, so that your receipts were ordered by date, like this:

2017-02-06 - The Party Place [party supplies]

Sure, you could manually rename this one file, but what if you have 500 receipts that you need to rename? Enter regular expressions—they’ll let you do this text manipulation, and many more. What follows is a very brief summary of my knowledge of regex, along with pointers to sites where I go when (very often) the problem I need to solve is beyond my regex skill level.

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Create a workload for your CPUs

Over the weekend, I was testing how some of our apps work when the CPUs are busy. One way to load the CPUs is to rip a Blu-ray disc, but I was looking for a more controllable CPU load.

A quick search through the Mac OS X Hints archive (use this tip to search the site) found the answer from 15 years ago: Just say yes in Terminal to generate sizable CPU loads…

More specifically, use this command in Terminal:

yes > /dev/null &

If there’s an award for strangest Unix utility, yes might just be the winner. All it does is output y (or whatever you list after the y; the man page suggests an expletive) until you kill the task.

The above command sends the output (via the > redirect) to the null device, which discards it. The ampersand sends the job to the background, so you get your Terminal prompt back.

You can run this command multiple times, each loading the CPU even more heavily (the screenshot shows three yes tasks running). Keep an eye on Activity Monitor to see just how much CPU it takes—as shown above, it does a great job at loading the CPU.

You can kill the tasks by issuing the command killall yes in Terminal, or by quitting Terminal—you’ll be told that quitting will terminate the tasks.

Install and configure Apache, PHP, and MySQL on macOS Sierra

Fair warning: Today’s tip is over-the-top geeky.

After many years of not doing anything with web serving on my local Mac, I recently had a need to look at some mySQL/PHP-based web packages. While I could install these on robservatory as tests, I generally like to install things locally first, because I’ll install a handful of packages until I find the one I like. But it’d been so long, I didn’t have anything configured. (Remember when enabling Apache—i.e. web sharing—was a feature of the System Preferences’ Sharing panel? Ah, good times!)

I could have opted to use the built-in Apache, but I wanted something that I could more easily keep up to date, and that, if I chose, would be easy to remove. The good news is that Homebrew has packages available for Apache, PHP, and MySQL. Homebrew installs everything in its own directory tree, and adding and removing packages is simple—exactly the setup I wanted.

So in theory, installation was as easy as three brew tap commands. The reality, though, is that the installation is a bit more complex. OK, it’s a lot more complex. The good news is that, this being the age of the internet, help is but a search away. Or the advice of a friend away, which is what I used in this case.

A friend pointed me to this excellent installion guide that walks through the entire process, including installing two versions of PHP with the ability to switch between them on the fly.

It was this on-the-fly switching, though, that gave me troubles: I couldn’t get a site to load unless I specified “index.php” or “index.html” as part of the URL. (Apache is configured to grab those files automatically.) Solving that one took a bit of time…

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Start Terminal sessions with a possibly-witty quote

Really long-time Unix users—as in mainframe-based Unix—are probably familiar with fortune. This silly little program grabs a random line from a collection of files holding quotes, sayings, jokes, etc. The Unix I used many decades ago would print an entry from fortune each time you started a new session. Here are some examples of what might greet me each time…

"It's a dog-eat-dog world out there, and I'm wearing Milkbone underware."
-- Norm, from _Cheers_

Mobius strippers never show you their back side.

All constants are variables.

Years ago, I had set up my Mac’s Terminal to output a fortune each time I opened a new session (window). At some point, though, I forgot to set it up on a new system, so it was gone. While fortune isn’t included in macOS’ Unix core by default, there are many ways to get it back, and it’s relatively simple to do so. Here’s one way…

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Easily create animated GIFs from video via ffmpeg

I recently explained how I captured a series of screenshots and turned them into a movie. While I was working on my tweet about the write-up, I thought an animated GIF of the final movie would be a nice way to show what it was I was trying to do. So that’s what I wound up doing:

So how did I create the animated GIF from the movie file? I know there are any number of great apps that will do this (ScreenFlow, for one), but I had another thought: While working on the animated screenshot movie (which I created using ffmpeg), I had happened to read about ffmpeg’s ability to create high quality animated GIFs, so I thought I’d give that a try.

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Get more details from transcode-video

While working on my massive Blu-ray ripping comparison, I wanted more information about what some of the transcode-video presets were doing. That is, if you pick --target big, exactly what settings are being used to rip the video?

It turns out there’s --dry-run option for transcode-video that will tell you exactly that. (I’ve added some line breaks for readability here.)

What’s neat is that you can also use this to see what the default options are for transcode-video when you don’t supply it with any options. Just use the --dry-run parameter option but leave off any of the presets (i.e. --target big), and the output will show you the defaults.

In addition, you can use it on already-ripped media to get their details as well, regardless as to how you ripped the movie.

In a related vein, I was having issues with the above rip, because I thought that the surround sound track wasn’t being ripped. Again, thanks to Don, I learned about a second command line option for transcode-video that reveals exactly what’s in a ripped video.

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Semi-automatic Homebrew and video-transcode updates

As I’ve written about in the past, I use Don Melton’s video transcoding tools to rip Blu-Ray discs. I also use Homebrew to install some of the transcode video dependencies, as well as other Unix tools.

Keeping these tools current isn’t overly difficult; it only requires a few commands in Terminal:

$ brew update
$ brew upgrade
$ sudo gem update video_transcoding

My problem is that I often forget to do this, because—unlike most GUI Mac apps and the Mac App Store—there’s no built-in “hey, there’s an update!” system. Suddenly, two months and many revisions later, I finally remember (usually when I see a tweet about a new version of something.) So I thought I’d try to write my own simple update reminder.

I didn’t really want a scheduled task, like a launchd agent—it’s not like these tools need to stay current on a daily basis. (And one of them needs to run with admin privileges, which complicates things.) I just wanted something that would remind me if it’d been a while since I last checked for updates, and then install the updates if I wanted it to do so.

After mulling it over, I came up with a script that runs each time I open a Terminal window (which I do daily). The referenced script looks at the date on a check file, and asks me if I’d like to check for updates if that date is more than a week older than today’s date. This is perfect for my needs: The reminder is automatic, but I can choose when to install the updates based on what I’m doing at the time. If it’s been under a week since I last checked, nothing at all is different about my Terminal launch.

Read on for the script and implementation details. (Note: This is not written for a Terminal beginner, as it assumes some knowledge about how the shell works in macOS.)

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