My personal doodle pad about everything that has anything to do with technology...
Let’s assume that an MP4 video file has two audio streams, but you only want to keep one.
The following line will create a new mp4 video file that only has the first audio stream:
ffmpeg -i input.mp4 -map 0:v:0 -map 0:a:0 -c copy output.mp4The following line will create a new mp4 video file that only has the second audio stream:
ffmpeg -i input.mp4 -map 0:v:0 -map 0:a:1 -c copy output.mp4(Last update on September 19, 2026 was done by Editor F.)
So, you have downloaded a file that is supposed to be a JSON. Before processing the file, it might be wise to check if that file is actually a valid JSON file.
Here is how to check if a file is indeed a valid JSON file:
if jq empty $File 2>/dev/null; then
ThisFileIsAValidJSONFile="true"
else
ThisFileIsAValidJSONFile="false"
fi (Last update on September 2, 2026 was done by Editor F.)
Sometimes, one wants to check if Apache2 is running. This is one way how to do it in BASH:
if [ "$(systemctl is-active apache2)" = "active" ]; then
echo "Apache2 is active"
ApacheIsRunning=1
else
echo "Apache2 is not active"
ApacheIsRunning=0
fi(Last update on September 1, 2026 was done by Editor F.)
Sometimes, one wants to put a nextcloud installation into “Maintenance mode” from the command line. Assuming your nextcloud is installed in /var/www/nextcloud/, the following command will put it in maintenance mode:
sudo -u www-data php /var/www/nextcloud/occ maintenance:mode --onThe following command will deactivate maintenance mode:
sudo -u www-data php /var/www/nextcloud/occ maintenance:mode --offIf you want to check the state of maintenance mode:
if [ "$(sudo -u www-data php /var/www/nextcloud/occ status | grep -c "maintenance: true")" != "0" ]; then
echo "Nextcloud is in maintenance mode"
else
echo "Nextcloud is not in maintenance mode"
fi
(Last update on September 2, 2026 was done by Editor F.)
Sometimes, one wants to put a yourls installation into “Maintenance mode” from the command line. Assuming your yourls is installed in /var/www/example.com/x/, the following command will put it in maintenance mode:
touch /var/www/example.com/x/.maintenanceThe following command will deactivate maintenance mode:
rm -f /var/www/example.com/x/.maintenance(Last update on September 1, 2026 was done by Editor F.)
Sometimes, one wants to put a wordpress installation into “Maintenance mode” from the command line. Assuming your wordpress blog is installed in /var/www/myblog.example.com/, the following command will put it in maintenance mode:
echo '<?php $upgrading = '"$(date +%s)"'; ?>' > /var/www/myblog.example.com/.maintenanceThe following command will deactivate maintenance mode:
rm -f /var/www/myblog.example.com/.maintenance(Last update on September 1, 2026 was done by Editor F.)