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.
Month: September 2018
I knew that day that the Shortcuts app has paved the way for automation in iPhone, but I didn’t realize that it can also be used to keep a track on the proliferating police abuse.
Source: This Siri Shortcut Automatically Triggers Camera Every Time Cops Pull You Over (Fossbytes)
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.
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.