Unix tips and tricks

Small things that save time

· Updated

I keep coming back to this story: in 1986, Jon Bentley asked Donald Knuth to demonstrate literate programming by writing a program to count word frequencies. Knuth wrote an elegant 10+ page solution. Doug McIlroy, asked to review Knuth’s work, offered an interesting counterpoint in just 6 lines of shell:

tr -cs A-Za-z '\n' | tr A-Z a-z | sort | uniq -c | sort -rn | sed ${1}q

Worth mentioning: this wasn’t a competition or a criticism. Knuth is one of the greatest programmers alive. He was demonstrating how to write complete programs from scratch. McIlroy was showing what happens when you compose small tools that already exist.

Once the Unix philosophy clicks, you start seeing these shortcuts everywhere. Here are the ones I actually use.

History

!! repeats the last command. sudo !! is your friend when you forget sudo.

!$ gets the last argument. Create a directory and cd into it:

mkdir /tmp/new
cd !$

^foo^bar runs the previous command replacing foo with bar. Great for typos.

Ctrl + r searches history. But if you install fzf, it replaces the default search with a fuzzy finder. Game changer. seriously, install fzf

Prevent accidents

I’ve lost files to careless rm and mv. Now I use these aliases:

alias cp='cp -i'
alias mv='mv -i'
alias rm='rm -i'

The -i flag asks before overwriting or deleting.

Readline shortcuts

Navigation:

  • Ctrl + a beginning of line
  • Ctrl + e end of line
  • Alt + b back one word
  • Alt + f forward one word

Editing:

  • Ctrl + w delete word backward
  • Ctrl + u delete to beginning of line
  • Ctrl + k delete to end of line
  • Ctrl + y paste what you deleted

Search:

  • Ctrl + r search history backward
  • Ctrl + g cancel search

Directory tricks

cd - returns to the previous directory.

mkdir -p creates nested directories:

mkdir -p project/{src,tests,docs}

For jumping to frequently used directories, zoxide learns your habits. After visiting a directory once, z project takes you there from anywhere.

Brace expansion

Copy a file with a new extension without typing the name twice:

cp config.json{,.backup}

Rsync

Once you use rsync, you never go back to scp. It only transfers what changed:

rsync -avz ./local/ user@server:/remote/

Quick commands

Pretty print JSON:

jq . file.json

If you don’t have jq installed: python3 -m json.tool file.json

Get your external IP:

curl ifconfig.me

Serve current directory over HTTP:

python3 -m http.server 8000

Empty a file:

> file.log

Job control

You started a long download and forgot to use nohup. Now you need to leave. Don’t cancel it:

Ctrl + z    # pause
bg          # resume in background
disown %1   # detach from session

Now you can close the terminal and the job keeps running.

macOS specific

Copy command output to clipboard:

cat file.txt | pbcopy

Paste from clipboard:

pbpaste > file.txt

Open files or URLs with default app:

open file.pdf
open https://example.com
open .   # opens current folder in Finder

Prevent sleep during a long task:

caffeinate -i long_running_script.sh

Quick Look from terminal:

qlmanage -p file.pdf 2>/dev/null

Flush DNS cache:

sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder