I call this the unofficial bash strict mode. This causes bash to behave in a way that makes many classes of subtle bugs impossible. You’ll spend much less time debugging, and also avoid having unexpected complications in production.
Source: Use the Unofficial Bash Strict Mode (Unless You Looove Debugging) (aaron maxwell)
Use iptables to create a VPN killswitch to protect against data leaks.
If you’re connected to a VPN, you need a killswitch. No, it’s not as metal as it sounds. It’s just a mechanism that stops your Internet connection when you’re disconnected from the VPN. It protects you from inadvertently leaking sensitive information onto the Internet when the VPN connection drops.
Source: How To Create A VPN Killswitch Using Iptables on Linux – LinuxConfig.org
The ls command is used to list directory contents and the results can be sorted upon several criteria such as by date, alphabetical order of filenames, modification time, access time, version and file size.
In this article, I will show you how to sort files by date using ls command in Linux.
Source: Guide to Sort Files by Date Using LS Commandline in Linux (LinOxide)
Ever wondered why programming in Bash is so difficult? Bash employs the same constructs as traditional programming languages; however, under the hood, the logic is rather different.
Source: Understanding Bash: Elements of Programming | Linux Journal
Every so often something really useful appears on Reddit, and this is such a case. You may encounter a situation where you want to execute the contents of a bash script, but not more frequently than every few seconds. A Reddit user wanted to know How to check if a command in .bashrc has been executed within last 10 seconds if yes don’t execute the command again. The response by Reddit user mdaffin is brilliant in its simplicity, and can be used in any bash script where you don’t want the contents executed too often:
Write a time stamp to some file, check said file before you run the command if now – timestamp > 10s run the command and update the timestamp.
EDIT: Like this (with modification times instead):
if [[ ! -f "$TS_FILE" ]] || [[ "$(expr "$(date +%s)" - "$(stat -c %Y "$TS_FILE")")" -gt 10 ]]; then
You’d replace the
echo "running" line with the part of the bash script you want to run only if it’s been 10 seconds since the last time the script was run, or whatever number of seconds you specify after the
-gt. If the bash script actually outputs a file as part of its normal operation then you could specify that file in the
TS_FILE= line; there would be no need to create a separate timestamp file (unless some other process could also modify that same file).
This doesn’t actually stop the bash script from running; it just prevents it from executing the part of the script that you don’t want executed too frequently. This could be very useful in a situation where without such protection, the too-frequent execution of the script might cause something undesirable to happen (such as getting locked out of an online site for hammering it with requests). Depending on the situation there may be other, perhaps even better ways to avoid this possibility, but in other cases this may indeed be the best approach.
Grepping is awesome, as long as you don’t glob it up! This article covers some grep and regex basics.
Source: Globbing and Regex: So Similar, So Different | Linux Journal
SSH-key-based authentication provides a more secure alternative to password-based authentication. In this tutorial we’ll learn how to set up SSH key-based authentication on a Debian 9 installation.
Source: How to Set Up SSH Keys on Debian 9 | DigitalOcean
We originally set out to do this because we were having problems getting an older model laser printer, specifically a Konica Minolta PP1350W, to work with MacOS High Sierra (10.13). With previous versions of MacOS we’d been able to connect the printer directly to the computer, and with some fiddling with drivers and other software, get it to work. But newer versions of MacOS seem to be far less tolerant of this, and we had a spare Raspberry Pi, so the idea came to us to use the Raspberry Pi as a bridge between the printer and any computers on the local network from which we wanted to be able to print. The bonus is that the printer is no longer tethered to a single machine, but instead can potentially be used by any computer on the local network.
You do not need to have a Raspberry Pi to make this work – any computer that can run Linux will do. And of course the Raspberry Pi or other Linux computer can be used for other purposes besides this. We do not guarantee that this technique will work for every older printer out there, but this will work with a surprising number of them.
Source: Convert an older model USB printer to a networked printer using a Raspberry Pi or other Linux-based computer — also works well for making an older printer compatible with a newer version of MacOS – Two “Sort Of” Tech Guys
This tutorial will provide you the ways to send emails from Linux command line. This is useful for sending email through our shell scripts, cron jobs etc.
Source: 5 Ways to Send Email From Linux Command Line | TecAdmin
Looking to take your Python code from the world of command lines and into the convenience of a GUI? Have a Raspberry Pi with a touchscreen that’s going to waste because you don’t have the time to learn a GUI SDK? Look no further, you’ve found your GUI package.
Source: PySimpleGUI (Github)
Note: Scroll down the page for instructions and sample usage. This really does seem like an easy way for Python users to add GUI interfaces to their Python scripts. The author has said in a Reddit post that “It’s based only on tkinter. Zero package dependencies. And it’s a single .py file. That means not much can go wrong.” And that it “Works in Windows, Linux, Mac. Running on my Pi board that has 3.4 installed on it.”