⌨️ how-to linux

or, the “the wisdom of the tee” part.

tl;dr

• absolute basics: cd, ls, rm, mv, vim
• shortcuts: [ctrl] + [a|e|c|k|z]
• intermediate: |, history, grep (ripgrep), cat, less, man, find (fd), df, du (dust), sudo, tail, touch, alias, sh, exit
• processes: &, >, top, ps, kill, killall, which, locate, fg
• network: curl, whois, traceroute, ping, lsof, scp
• handy commands: SSH key generation, handling archives, replacing en masse, permissions, JSON parsing, shell script checks, zx

learning how to use the terminal of your computer is a console without any buttons. you are expected almost to know which “buttons” are hidden there below the surface. no one ever gave me a primer and it was painful to learn over time through trial and error what those hidden commands are. here’s a compilation of some useful commands to get you through most basic functions and some more interesting ones.

btw, god help you if you need to write shell scripts. ugh, i think they’re the worst syntactically. my tendency is to write node or python scripts instead because at least they make bore sense to me.

absolute basics

• cd [name] — change directory
  • ~ is shorthand for your home directory
  • .. is shorthand for the parent directory
  • . is shorthand for the current directory
  • - is shorthand for the previous directory you were in (like your browser’s “back” button)
  • e.g. cd .. will take you to the parent directory
• ls — list contents of the directory you’re in
  • ls -lah is useful to list hidden files as well
• rm [file] — remove a file
  • rm -r [file] — remove a directory
• mv \[origin\] [destination] — move a file somewhere else
  • clear — also, clears screen
• vim [file] — edit a file
  • i to go to insert mode
  • esc to go back to command-mode
  • / to search in the file
  • :w (in command mode) to save
  • :q (in command mode) to quit

shortcuts

this is a pet peeve of mine that no one ever taught me these super handy shortcuts and i didn’t know about them for many years.

[ctrl] + a — go to beginning of the line [ctrl] + e — go to the end of the line [ctrl] + c — kill the currently running program [ctrl] + k — clear screen [ctrl] + z — pause the currently running program

intermediate

• | — the “pipe”. pass the output from one process to another, e.g. history | grep cd
• history — see the list of commands you’ve tried in the past
• grep [pattern] * — search the files in the current directory for the pattern
  • tip: easier, faster alternative is ripgrep, you can install via brew install ripgrep
• grep [pattern] * -rsiI — search recursively, case-insensitive, ignoring binary files
• history | grep [pattern] — find relevant commands in your history you’ve used before
• cat [file] — output the contents of a file
• less [file] — scroll through the contents of a file (space to page through, q to quit)
• man [command] — show help file for a command, [cmd] -h or [cmd] --help also can work
• find . -name '[file]' — find a file by a specific name
  • tip: easier alternative is fd, you can install via brew install fd
• df -h — show local hard disk space
• du -sch * |sort -hr — show the biggest files under a particular subdirectory
  • tip: easier alternative is dust, you can install via brew install dust
• sudo [command] — run command with elevated privileges
• tail -f [file] — see real-time updates to a file, used especially with a log file on a server
• touch [file] — creates file if doesn’t exist, or updates its timestamp
  • useful to kick off a process that might be waiting for a file to change before running
• alias [shortcut]='[command to run]' — take a long command that’s hard to remember and create a shortcut for it, e.g. alias v='ls -lah'
• sh — open up another shell (zsh if you’re using that)
  • exit — to exit the shell

processes

• [cmd] & — adding the ampersand at the end of a command will run it in the background
• [cmd] > output.txt — adding a > will save output of the program to a particular file
• top — find out what’s current running on your machine
• ps aux — see the processes currently running on your machine
• ps aux | grep [name] — super common way to find the process you’re looking for
• kill [process id] — you can grab a process id from the ps aux list and kill it
• killall [name] — kill process(es) matching the name
• which [command] — find out the directory where a program lives
• locate [pattern] — find files on your local machine matching the pattern (macOS only)
• fg — start a paused program again (via [ctrl] + z), or, use bg to run it in the background

network

• curl -O [url] — retrieve a webpage and save it disk
• whois [domain] — find out info about a particular website
• traceroute [domain] — show computer hops from router to router to a destination
• ping [domain] — simple test to see if a website is up or not
  • ping6 [domain] — same as above, but for IPv6
• lsof -i :[port] — see which process is using which port.
  • lsof -t -i tcp:[port] | xargs kill -9 — to easily kill whatever’s on a port.
• scp username@remotehost:/path/to/file /path/to/save/locally — copy a file from a remote server

handy commands

• ssh-keygen -t rsa -b 4096 -C "[example@email.com]" — generate SSH key
• ssh-add -K ~/.ssh/id_rsa — add password to your keychain to save time
• tar -czvf \[name\] [file] — compress a file/directory into an archive
• tar -xzvf [file] — uncompress an archive
• grep [pattern] * -rsiIl | xargs sed -i '' s/[pattern]/[replacewith]/g —
  • replace a pattern in all the files found recursively within a particular directory
• sudo chown -R $USER:$USER file — transfer ownership of a directory and its files to yourself
• jq '[selector]' < example.json — if your server logs are in JSON format you can query them using the jq command
• fc — fix command. open up the last command you tried to run in an editor.
• <( somecommand ) — treat a command output as a file. e.g. try diff <(ls) <(ls -a)
• cmatrix — make it look like you’re doing something important 😉
• shellcheck — check your shell script for errors before running it.
• zx — a handy JS tool around shell scripting that makes running multiple commands a little more intuitive for those of us that don’t live on the command line day-to-day (i.e. most of us).