Create filelist to merge
ls *.avi | while read each; do echo "file '$each'" >> mylist.txt; done
use ffmpeg to concatenate files.
ffmpeg -f concat -i mylist.txt -c copy video_draft.avi

search text in file
find /path/to/folder -type f -exec grep -H "search_term" {} \;

show all dirs & files with size and sort by size
du -sh | sort -n

find files bigger than 20M
find . -type f -size +20M

awk

find all not matching (EXACT!!!) "#" and copy to new file
awk '$0!="#"' config >> config_clean

find all mathing/not matching PATTERN

awk '/#/' config
awk '!/#/' config

expand to 1:1 aspect ratio and resize
magick input.png -gravity center -background none -extent 145 -resize 128 output.png
create icon from file
magick code-logo.png -define icon:auto-resize=128,64,48,32,16 code-logo.ico
convert to avif
magick input.png -define heic:speed=2 output.avif

log in on A as user a and generate a pair of authentication keys. all commands from a@A:~>

ssh-keygen -t rsa

create a directory ~/.ssh as user b on B.

ssh b@B mkdir -p .ssh

append a's new public key to b@B:.ssh/authorized_keys:

cat .ssh/id_rsa.pub | ssh b@B 'cat >> .ssh/authorized_keys'

ln -s /path/to/file /path/to/symlink