CS - Unix, Shell, and alike

Terminal

Shell

A personal cheat sheet of Unix / macOS terminal commands, shortcuts and workflows.

Published

July 22, 2026

A personal collection of terminal commands, keyboard shortcuts and small workflows I keep coming back to on Unix and macOS.

Terminal — useful commands

Command	What it does
`diff -w file1 file2 > diff.txt`	Compare two files ignoring whitespace and save the differences to a file.
`open -a Application file`	macOS: open a file with a specific application.
`echo -e "first_line\nsecond_line"`	Print text interpreting escape sequences such as `\n` (newline); `-e` enables them.
`ssh -v user@gateway -t ssh user@internal`	Verbose SSH that jumps through a gateway/firewall host to reach an internal host.
`sshfs user@host:/remote/dir /local/dir`	Mount a remote directory over SSH as if it were a local folder.
`screen -S name`	Start a named, detachable terminal session that keeps running in the background.
`curl "url" -O`	Download/transfer data from a URL (the Unix counterpart to `wget`); `-O` saves it to a file.
`echo "hello, world!"` \| `tee file.txt`	Print to the screen and write the same output to a file at once.
`iconv -f utf-8 -t iso-8859-1 in.txt > out.txt`	Convert a text file from one character encoding to another.
`file -I filename`	Show a file’s type and character encoding (`-I` on macOS, `-i` on GNU/Linux).
`nmap -n -sn 10.0.0.0/24`	Ping-scan a subnet to discover live hosts (`-sn`; the old `-sP` is deprecated).
`top -d seconds`	Monitor running processes, refreshing every N seconds.
`awk '{print FNR "\t" $0}' file.txt` \| `open -f`	Prepend pseudo line numbers and open the result in TextEdit (macOS; use ⌥+drag for column selection).

Terminal — keyboard shortcuts

These are the default Emacs-style line-editing bindings in bash/zsh.

Shortcut	Action
`Ctrl` + `A`	Move to the beginning of the line.
`Ctrl` + `E`	Move to the end of the line.
`Ctrl` + `U`	Delete from the cursor back to the beginning of the line.
`Ctrl` + `K`	Delete from the cursor to the end of the line.
`Ctrl` + `W`	Delete the word before the cursor.
`Ctrl` + `Y`	Paste (yank) the text that was just deleted.
`Ctrl` + `C`	Cancel / interrupt the current command.
`Ctrl` + `L`	Clear the screen.
`Ctrl` + `R`	Reverse-search command history; press again to step through matches.

`screen` shortcuts

Shortcut	Action
`Ctrl` + `A`, then `D`	Detach from the current `screen` session (it keeps running).
`Ctrl` + `A`, then `[`	Enter scrollback / copy mode.

Sun Grid Engine essentials

Basic job-scheduling commands on a Sun Grid Engine (SGE) cluster.

Command	What it does
`qsub script.sh`	Submit a job to the queue.
`qdel jobid`	Delete/cancel a job; `qdel -u user` cancels all of a user’s jobs.
`qstat -f`	Show the full status of queues and jobs.
`qstat -j jobid`	Show detailed information about a specific job.
`qstat -explain c`	Explain why a queue/job is in a given state.
`qstat -F attribute`	List queues filtered by resource attributes.
`qhost -j`	List cluster hosts together with the jobs running on them.

macOS — fast symbols with the Option key

Hold ⌥ Option and press a key (US keyboard layout). Entries marked (dead key) combine with the next character you type — e.g. ⌥+e then a gives á.

Keys	Symbols
`⌥` + `1 2 3 4 5 6 7 8 9 0`	¡ ™ £ ¢ ∞ § ¶ • ª º
`⌥` + `q w e r t y u i o p`	œ ∑ ´ ® † ¥ ¨ ˆ ø π
`⌥` + `a s d f g h j k l`	å ß ∂ ƒ © ˙ ∆ ˚ ¬
`⌥` + `z x c v b n m`	Ω ≈ ç √ ∫ ˜ µ
`⌥` + `=`	≠
`⌥` + `[ ] \`	” ’ «
`⌥` + `; '`	… æ
`⌥` + `, . /`	≤ ≥ ÷

Combine with Shift for a second set of symbols:

Keys	Symbol
`⌥` + `Shift` + `K`	Apple logo ()
`⌥` + `Shift` + `2`	€
`⌥` + `Shift` + `8`	°
`⌥` + `Shift` + `V`	◊

Dead keys: ⌥+e = acute (´), ⌥+u = umlaut (¨), ⌥+i = circumflex (ˆ), ⌥+n = tilde (˜).

Miscellaneous workflows

Record a voice-over with `say`

macOS can read a text file aloud and save it as audio:

say -f file.txt -o output.aiff -r <words_per_minute> -v <voice>

-v picks a voice (e.g. Alex, Bruce, Luciana). List installed voices with say -v '?'.

`.zshrc` and `.zshenv`

macOS uses Z shell as the default shell.

Put your preferences in ~/.zshrc, then reload them with source ~/.zshrc.
If you already have a .bash_profile, the quickest way to keep things working is to source it from a .zshenv:

echo 'source ~/.bash_profile' > ~/.zshenv && source ~/.zshenv

See this discussion.

Convert image files in batch

Replace FORMAT with png, jpeg or tiff and EXT with the matching extension (EPS may not work):

for i in *; do sips -s format FORMAT "$i" --out "${i%.*}.EXT"; done

Or with ImageMagick:

brew install imagemagick
magick A.jpg A.png   # `magick convert` on older ImageMagick 6

Create a password-protected ZIP file

zip -er file.zip folder_to_zip/

-e encrypts the archive (prompts for a password); -r adds the folder recursively.

Install Jekyll on Apple silicon (M1/M2)

Jekyll is a solid backend for static sites, but on Apple silicon the system Ruby can cause architecture problems. A reliable workaround:

Don’t use the Ruby bundled with macOS — install it from Homebrew, following the official steps.
Homebrew’s Ruby is keg-only and not symlinked, so add it (and the gem executables) to ~/.zshenv:

export PATH="/opt/homebrew/opt/ruby/bin:$PATH"
export PATH="$HOME/.gem/ruby/3.1.0/bin:$PATH"

Restart the shell and confirm ruby -v points to the Homebrew version.
Install jekyll, bundler and webrick (the last one is required) locally:

gem install --user-install bundler jekyll webrick

Convert `.m4a` to `.mp3`

brew install ffmpeg
ffmpeg -i in.m4a -codec:a libmp3lame -qscale:a 1 out.mp3

Remove printing restrictions from a PDF

brew install qpdf
qpdf --decrypt in.pdf out.pdf

Convert a PDF to plain text

brew install xpdf
pdftotext -enc UTF-8 in.pdf out.txt

Merge PDFs from the command line

Use pdfunite (part of Poppler). It may conflict with xpdf, since both depend on Poppler:

pdfunite in1.pdf in2.pdf merged.pdf