unix

How to use the Linux ‘scp’ command without a password to make remote backups

Summary: How to create a public and private key pair to use ssh and scp without using a password, which lets you automate a remote server backup process.

Over the last two years I've ended up creating a large collection of websites and web applications on a variety of Linux servers that are hosted with different companies like GoDaddy and A2 Hosting. I recently embarked on a mission to automate the backup processes for all these sites, and as a result of this effort, I thought I'd share what I've learned here.

Linux crontab examples (every X minutes or hours)

Table of Contents1 - Linux crontab: How to run a command every minute2 - Descriptions of the crontab date/time fields3 - Run a crontab command every hour4 - Run a crontab entry every day5 - Run a crontab entry every 5 minutes6 - Unix and Linux “crontab every” summary7 - Unix and Linux crontab reference information

Linux crontab FAQ: How do I schedule Unix or Linux crontab jobs to run at intervals, like “Every five minutes,” “Every ten minutes,” “Every half hour,” and so on?

Solution: I’ve posted other Unix/Linux crontab tutorials here before (How to edit your Linux crontab file, Example Linux crontab file format), but I’ve never included a tutorial that covers the “every” options, so here are some examples to demonstrate this crontab syntax.

How to fire MacOS notifications with AppleScript and Scala

Table of Contents1 - A “Hello, world” MacOS AppleScript notification2 - AppleScript: Mac notification with a sound3 - How to add a title and subtitle to your notification4 - Running from Scala (or Java)5 - See also6 - Summary

Summary: This tutorial demonstrates how to fire MacOS system notifications with AppleScript and Scala (or Java).

In this article it helps if you already know a little bit about AppleScript, though that’s not completely necessary. Near the end of the tutorial I show how to invoke the AppleScript code using Scala, so feel free to skip down to there if you just want to see that — you can always read the stuff at the top for reference later.

Unix/Linux: Find all files that contain multiple strings/patterns

When using Unix or Linux, if you ever need to find all files that contain multiple strings/patterns, — such as finding all Scala files that contain 'try', 'catch', and 'finally' — this find/awk command seems to do the trick:

find . -type f -name *scala -exec awk 'BEGIN {RS=""; FS="\n"} /try/ && /catch/ && /finally/ {print FILENAME}' {} \;

As shown in the image, all of the matching filenames are printed out. As Monk says, you’ll thank me later. :)

(I should mention that I got part of the solution from this gnu.org page.)

Linux/Unix: How to copy a directory and save the date/time file information

If you need to copy a directory on Unix/Linux and want to preserve the date/time information while copying the directory and files, use the -p option to save the date/time information, and the -r option to copy the directory properly. For instance, I just used this cp command to copy a directory named OldDir to a new directory named NewDir, while retaining all of the date/time file information:

Using find and grep to print lines before and after what you’re searching for

A cool thing about the Unix/Linux grep command is that you can show lines before and after a pattern match with the -B and -A options. As an example, I just used this combination of find and grep to search for all Scala files under the current directory that contain the string null. This command prints five lines before and after each null line in each file:

$ find . -type f -name "*.scala" -exec grep -B5 -A5 null {} \;

That’s good stuff, but it prints a really long list of lines, and I can’t tell the output of one file from another. To fix this, I put the following code in a file named helper.sh, and made it executable:

A shell script to change between MacOS dark mode and light mode

If you want to create a shell script so you can change between MacOS dark mode and light mode from the Terminal (Unix) command line, put this source code in a file and name it something like dark:

osascript -e \
'tell application "System Events" to tell appearance preferences to set dark mode to not dark mode'

Then make that file executable, and make sure it’s on your PATH. Now you can type dark to toggle back and forth between dark mode and the regular light mode:

Jeyes, a Java version of Xeyes

Jeyes, a Java version of Xeyes

In my spare time back in 2011 I created a Java version of the old Unix/X-Windows “Xeyes” application. If you ever used Xeyes, you know it as a set of eyes that are displayed on-screen, and follow the mouse cursor as you move it around.

Now in 2019 I just brought it back to life, and here’s a 56-second video that shows how it works:

How to easily determine the blocksize of a filesystem

I just saw that this is a way you can easily determine the blocksize of a filesystem, at least a Mac/Unix/Linux filesystem:

$ echo foo > foo

$ du -h foo
4.0K    foo

I tried to do the same thing with touch foo, but that didn’t work. Without digging into it more, the key seems to be in having very little text in the file, at which point the du command shows the minimum block size for the file.