when I forget to include sudo in my command:

sudo !!

I use $_ a lot, it allows you to use the last parameter of the previous command in your current command

mkdir something && cd $_

nano file
chmod +x $_

As a simple example.

If you want to create nested folders, you can do it in one go by adding -p to mkdir

mkdir -p bunch/of/nested/folders

Good explanation here:
https://koenwoortman.com/bash-mkdir-multiple-subdirectories/q

Sometimes starting a service takes a while and you're sitting there waiting for the terminal to be available again. Just add --no-block to systemctl and it will do it on the background without keeping the terminal occupied.

systemctl start --no-block myservice

Ctrl-z to suspend the running program.

bg to make it continue running in the background.

jobs to get an overview of background programs.

fg to bring a program to the foreground.

It isn't a command but an application. I cannot do my work without it.

screen

I only recently started using C-r to search in the command history. Game changer!

The watch command is very useful, for those who don't know, it starts an automated loop with a default of two seconds and executes whatever commands you place after it.

It allows you to actively monitor systems without having to manually re-run your command.

So for instance, if you wanted to see all storage block devices and monitor what a new storage device shows up as when you plug it in, you could do:

watch lsblk

And see in real time the drive mount. Technically not "real time" because the default refresh is 2 seconds, but you can specify shorter or longer intervals.

Obviously my example is kind of silly, but you can combine this with other commands or even whole bash scripts to do some cool stuff.

find /path/to/starting/dir -type f -regextype egrep -regex 'some[[:space:]]*regex[[:space:]]*(goes|here)' -exec mv {} /path/to/new/directory/ \;

I routinely have to find a bunch of files that match a particular pattern and then do something with those files, and as a result, find with -exec is one of my top commands.

If you're someone who doesn't know wtf that above command does, here's a breakdown piece by piece:

• find - cli tool to find files based on lots of different parameters
• /path/to/starting/dir - the directory at which find will start looking for files recursively moving down the file tree
• -type f - specifies I only want find to find files.
• -regextype egrep - In this example I'm using regex to pattern match filenames, and this tells find what flavor of regex to use
• -regex 'regex.here' - The regex to be used to pattern match against the filenames
• -exec - exec is a way to redirect output in bash and use that output as a parameter in the subsequent command.
• mv {} /path/to/new/directory/ - mv is just an example, you can use almost any command here. The important bit is {}, which is the placeholder for the parameter coming from find, in this case, a full file path. So this would read when expanded, mv /full/path/of/file/that/matches/the/regex.file /path/to/new/directory/
• \; - This terminates the command. The semi-colon is the actual termination, but it must be escaped so that the current shell doesn't see it and try to use it as a command separator.

I'd say that journalctl is not only boot, but every service that runs on the computer has its logs collected through it, so you can use it as journalctl --grep="your regex". You can also add -k to check kernel logs, -b -n to check nth precedent boot or -b n to check the absolute nth boot. There is a lot that you can check with it and it is quite nice :)

Otherwise, I like eza as an ls replacement, or batcat as a human friendly cat

nc is useful. For example: if you have a disk image downloaded on computer A but want to write it to an SD card on computer B, you can run something like

user@B: nc -l 1234 | pv > /dev/$sdcard

And

user@A: nc B.local 1234 < /path/to/image.img

(I may have syntax messed up--also don't transfer sensitive information this way!)

Similarly, no need to store a compressed file if you're going to uncompress it as soon as you download it---just pipe wget or curl to tar or xz or whatever.

I once burnt a CD of a Linux ISO by wgeting directly to cdrecord. It was actually kinda useful because it was on a laptop that was running out of HD space. Luckily the University Internet was fast and the CD was successfully burnt :)

echo 'dXIgbW9tCmhhaGEgZ290dGVtCg==' | base64 -d

I'm a big enjoyer of pushd and popd

so if youre in a working dir and need to go work in a different dir, you can pushd ./, cd to the new dir and do your thing, then popd to go back to the old dir without typing in the path again

systemd-run lets you run a command under some limitations, ie

systemd-run --scope -p MemoryLimit=1000M -p CPUQuota=20% ./heavyduty.sh

https://blog.sanctum.geek.nz/series/unix-as-ide/

# list all recursive files sorted by size  
$ fd -tf "" -x du -h | sort -h  
8.0K      ./asdfrc  
 20K      ./nvim/lua/lush_theme/bleak.lua  
 32K      ./alacritty.yml  

# find files by extension  
$ fd -e lua  
nvim/colors/bleak.lua  
nvim/init.lua  
nvim/lua/config/autocmds.lua  

# list found files in tree view  
$ fd -e lua | tree --fromfile  
.  
└── nvim  
    ├── colors  
    │   └── bleak.lua  
    ├── init.lua  

# Run "npm test" when a file changes in the src or test directories  
$ fd src test | entr -- npm test  

# find out how often you use each command  
history | cut -d " " -f 1 | sort | uniq -c | sort -n | tail -n 10  
  80 rm  
  81 lsd  
 107 asdf  
 136 npx  
 161 find  
 176 fd  
 182 cd  
 185 rg  
 247 brew  
 250 nb  
 465 npm  
 867 git  

Another one of my favorite is ctrl+r to quickly search for a previous command.

Then type in a word from the command you are looking for and then hit tab to find the right command if there is more than one with that word.

Search for github repos of dotfiles and read through people's shell profiles, aliases, and functions. You'll learn a lot.

Something that really improved my life was learn to properly use find, grep, xargs and sed. Besides that, there are these two little 'hacks' that are really handy at times...

1- find out which process is using some local port (i.e. the modern netstat replacement):

$ ss -ltnp 'sport = :<port-number>'

2- find out which process is consuming your bandwidth:

$ sudo nethogs

Not a command but the tab key for auto complete. This made it much easier for me.

parallel, easy multithreading right in the command line. This is what I wish was included in every programming language's standard library, a dead simple parallelization function that takes a collection, an operation to be performed on the members of that collection, and optionally the max number of threads (should be the number of hardware threads available on the system by default), and just does it without needing to manually set up threads and handlers.

inotifywait, for seeing what files are being accessed/modified.

tail -F, for a live feed of a log file.

script, for recording a terminal session complete with control and formatting characters and your inputs. You can then cat the generated file to get the exact output back in your terminal.

screen, starts a terminal session that keeps running after you close the window/SSH and can be re-accessed with screen -x.

Finally, a more complex command I often find myself repeatedly hitting the up arrow to get:

find . -type f -name '*' -print0 | parallel --null 'echo {}'

Recursively lists every file in the current directory and uses parallel to perform some operation on them. The {} in the parallel string will be replaced with the path to a given file. The '*' part can be replaced with a more specific filter for the file name, like '*.txt'.

List open files sudo lsof -i -P

Network traffic by hardware sudo tcpdump -i en1 -nn -s0

Current processes top -l 1

ripgrep

fzf is great for quickly finding files e.g. in large code repositories.

tcpdump can help diagnose network issues.

I'm not much of a one-liner collector but I like this one:

vim +copen -q <(grep -r -n <search> .) 

which searches for some string and opens all instances in vim's quickfix list (and opens the quickfix window too). Navigate the list with :cn and :cn. Complex-ish edits are the obvious use case, but I use this for browsing logs too.

Neovim improves on this with nvim -q - and [q/]q, and plenty of fuzzy finder plugins can do a better version using ripgrep, but this basic one works on any system that has gnu grep and vim.

Edit:

This isn't exactly a command, but I can't imagine not knowing about this anymore:

$ man grep
/  -n       # double space before the dash!

brings you directly to the documentation of the -n option. Not the useless synopsis or any other paragraphs that mention -n in passing, but the actual doc for this option (OK, very occasionally it fails due to word wrap, but assuming the option is documented then it works 99% of the time).

Bash/ZSH aliases are invaluable for commands that you run often. I use micro as my terminal editor so I have alias m for micro and sm for sudo micro. Just 2 of maybe a dozen aliases I use. Docker has quite a large list of aliases with ZSH. Super super useful. 

pkill journalctl -b nvtop tail are great but I like: LANGUAGE=en_GB LC_ALL=en_GB.UTF-8 LANG=en_GB.UTF-8 <your GUI program> to run a GUI program in English for more universal compatibility for helping newbies and creating/reading non-terminal based documentation

I get a lot of mileage out of the line editing commands. I think they are Emacs based and optional... but like Ctrl k, Ctrl u, Ctrl a.

(Fixed the bolding issue)

From a file I keep since I started using Linux near 5 years ago:

Display the RAM usage:
watch -n 5 free -m
Useful if you open way too much stuff and/or you're running on budget processing power, and don't want your computer freezing from 3 hours.
Also useful if you use KDE's Konsole integrated into the Dolphin file manager and you must for some reason not close the Dolphin window. You'd just need to open Dolphin's integrated Konsole (F4), run the command and without closing it, press F4 again to hide the Konsole.

Terminal-based file browser that sorts by total size:
ncdu
why is the cache folder 50 GB big?

Mass-check MD5 hashes for all files in the path, including subfolders:
find -type f \( -not -name "md5sum.txt" \) -exec md5sum '{}' \; > md5sum.txt
Change md5sum (and optionally the output file's name) for your favorite/needed hash calculator command.

For mounting ISOs and similar formats:
sudo mount -o loop path/to/iso/file/YOUR_ISO_FILE.ISO /mnt/iso

And unmounting the file:
sudo umount /mnt/iso
Beware there's no N in the umount command

For creating an ISO from a mounted disc:
dd if=/dev/cdrom of=image_name.iso

And for a folder and its files and subfolders:
mkisofs -o /path/to/output/disc.iso /path/from/input/folder

Compress and split files:
7z -v100m a output_base_file.7z input_file_or_folder

Changes the capslock key into shiftlock on Linux Mint (not tested in other distros):
setxkbmap -option caps:shiftlock
Was useful when the shift key from a previous computer broke and I didn't have a spare keyboard.

If you want to run Japanese programs on Wine, you can use:
LC_ALL=ja_JP wine /path/to/the/executable.exe
There are other options but this is one that worked the better for me so I kinda forgor to take note of them.

List all files in a given path and its subfolders:
find path_to_check -type f
Tip: add > output.txt or >> output.txt if you'd rather have the list in a TXT file.

Running a program in Wine in a virtual desktop:
wine explorer /desktop=session_name,screen_size /path/to/the/executable.exe

E.g.:
wine explorer /desktop=MyDesktop,1920x1080 Game.exe

Useful if you don't want to use the whole screen, there are integration issues between Linux, Wine and the program, or the program itself has issues when alt-tabbing or similar (looking at you, 2000's Windows games)

Download package installers from with all their dependencies:
apt download package_name
Asks for sudo password even when not running as sudo. Downloaded files come with normal user permissions thankfully. Also comes with an installation script but if you want to run it offline, iirc you need to change apt install in the script for dpkg -i.

If you use a program you'd rather not connect to the internet but without killing the whole system's connection, try:
firejail --net=none the_command_you_want_to_run

Or if you want to run an appimage:
firejail --net=none --appimage the_command_you_want_to_run

If you want to make aliases (similar to commands from Windows' PATH) and your system uses bash, edit the file $HOME/.bashrc (e.g. with Nano) and make the system use the updated file by either logging out and in, or running . ~/.bashrc

Python/Pip have some nifty tools, like Cutlet (outputs Japanese text as Romaji), gogrepoc (for downloading stuff from your account using GOG's API), itch-dl (same as gogrepoc but for Itch.io), etc. If you lack the coding skills and doesn't mind using LLMs, you could even ask one to make some simpler Python scripts (key word though: simpler).

If you want to run a video whose codec isn't supported by your system (e.g. Raspberrian which only supports H.264, up to 1080p):
ffmpeg -i input_video.mkv -map 0 -c:v libx264 -preset medium -crf 23 -vf scale=1920:1080 -c:a copy -c:s copy output_video.mkv

sudo shutdown 0

Prevents 99% of bugs and mistakes

ripgrep has mostly replaced grep for me, and I am extremely conservative about replacing core POSIX utilities - muscle memory is critical. I also tend to use fd, mainly because of its forking -x, but its advantages over find are less stark þan rg's improvements over grep.

nnn is really handy; I use it for everything but the most trivial renames, copies, and moves - anyþing involving more þan one file. It's especially handy when moving files between servers because of þe built-in remote mounting.

cd `pwd`

for when you want to stay in a dìr that gets deleted and recreated.

cat /proc/foo/exe > program
cat /proc/foo/fd/bar > file

to undelete still-running programs and files still opened in running programs