linux shell

bash 5+ / POSIX 2017

Quick reference for everyday Linux / macOS shell commands: file operations, text processing, permissions, processes, networking, archive and storage — with common options and practical examples.

40 commands

Files & Navigation

pwd

Print the absolute path of the current working directory.

pwd

ls

List directory contents.

-l long format; -a include hidden; -h human sizes; -t sort by mtime; -r reverse

ls -lah /var/log

cd <dir>

Change the current working directory.

cd ~/-projects/app && pwd

tree <dir>

Recursively list a directory as a tree; great for overview (may need install).

-L <n> max depth; -a show hidden; -d dirs only; -I pattern

tree -L 2 -I 'node_modules|.git' .

File Operations

mkdir -p <dir>

Create a directory (and any missing parents) in one shot.

-p create parents; -v verbose; -m <mode> set permissions

mkdir -p src/components/ui

cp <src> <dest>

Copy files or directories.

-r recursive (for dirs); -i interactive; -v verbose; -p preserve mode/time

cp -rv src/ backup/

mv <src> <dest>

Move (rename) files or directories.

-i interactive; -v verbose; -n no-overwrite

mv README.md readme.md && mv ../tmp .

rm <path>

Remove files or directories. ⚠️ there is no trash — double-check paths.

-r recursive; -f force; -i interactive; -v verbose

rm -rf build/ node_modules/

ln -s <target> <link>

Create a symbolic link at <link> pointing to <target>.

-s symbolic (default: hard); -f overwrite existing; -n do not follow existing

ln -s /opt/app-v2 current

touch <file>

Create an empty file or update its mtime without changing contents.

touch .gitignore

Text & Viewing

cat <file>

Print the entire contents of a file to stdout.

-n number lines; -A show non-printing chars; -s squeeze blanks

cat -n package.json

less <file>

Open a file in a paginator (use /, n, N to search; q to quit).

-N line numbers; -S no wrap; +F auto-follow tail-like

less -NS /var/log/syslog

head -n 10 <file>

Output the first N lines (default 10) of a file.

head -n 30 /etc/passwd

tail -n 50 -f <file>

Show the last N lines and follow the file as it grows (for logs).

-f follow; -F follow & retry; -n lines (default 10); -c bytes; --pid=PID stop when PID dies

tail -f -n 50 /var/log/nginx/access.log

Search & Filter

grep <pattern> <files>

Search lines matching a pattern; supports extended and PCRE regex.

-i case-insensitive; -r recursive; -n line numbers; -v invert; -E extended regex

grep -rni "TODO" src/

find <path> -name <pattern>

Walk a directory tree and list files matching criteria.

-type f|d; -name glob; -iname case-insensitive; -size +1M; -mtime -7; -maxdepth

find . -type f -name "*.log" -mtime +7 -delete

awk '<prog>' <file>

Pattern-action text scanner — slicing columns, summing values, etc.

-F fs field separator; -v var=value; -f script file

awk -F'\t' 'NR>1 {sum+=$3} END {print sum}' data.tsv

sed 's/<a>/<b>/' <file>

Stream editor — substitution, deletion, insertion per-line.

-i edit in place; -E extended regex; -e combine exprs; s/from/to/[g] [p]

sed -i '' 's/version = "1\.."/version = "1.9"/' pyproject.toml

sort | uniq -c | sort -nr

Pipeline idiom: count occurrences and sort by frequency descending.

awk '{print $1}' access.log | sort | uniq -c | sort -nr | head

Permissions

chmod <mode> <file>

Change file permissions (e.g., 755, u+x, g-w, o=r).

-R recursive; --reference=<file> copy mode

chmod -R u=rwX,go=r ./docs

chown <user>[:<group>] <file>

Change file owner and group.

-R recursive; -h affect symlinks (with -R)

chown -R www-data:www-data /var/www/html

umask

Show/set the default permission mask for newly created files.

-S symbolic; -p umask preserved for portability

umask 022

Processes & System

ps aux

Show all processes with detailed info (BSD-style columns).

-e all; -f full; -L threads; --sort=-%mem

ps auxf | grep -v grep | grep nginx

top / htop

Live, interactive process viewer (htop has nicer UI; may need install).

P/CPU M/MEM sort; k kill; r renice; q quit

htop -u www-data

kill [-9|<sig>] <pid>

Send a signal to a process. SIGTERM (15) is polite; SIGKILL (9) is forceful.

-9 SIGKILL; -l list signals; -s specify signal by name

kill -TERM 12345 && sleep 2 && kill -9 12345

jobs / bg / fg / nohup

Manage job control — list, background, foreground, run immune to hangups.

nohup ./long-task.sh > out.log 2>&1 &

systemctl <verb> <unit>

Control systemd services and units (status, start, stop, enable, logs).

status / start / stop / restart / enable / disable; -u <user>

systemctl status nginx && systemctl reload nginx

Network

wget <url>

Non-interactive downloader; recursive / mirror friendly.

-c continue; -q quiet; --no-check-certificate; -r recursive

wget -c https://example.com/big-archive.tar.gz

ssh <user>@<host> [cmd]

Open an SSH session or run a one-off command on a remote host.

-p <port>; -i <key>; -L / -R / -D port forwardings; -N no remote cmd; -f background

ssh -i ~/.ssh/id_ed25519 user@host 'sudo systemctl restart nginx'

scp / rsync

Copy files to/from a remote host. rsync is faster for partial / repeated transfers.

scp -r / rsync -avz --progress src/ user@host:/dst/

rsync -avz --progress ./build/ deploy@server:/srv/app/

ping / traceroute / ss

Diagnose reachability, path and listening sockets.

ping -c N count; ss -tulnp listen info; ss -s summary

ss -tulnp | grep -E ':80|:443'

Archive & Compress

tar -czf out.tgz <paths>

Create or extract tar archives, optionally with gzip/bzip2/xz.

-c create; -x extract; -t list; -z gzip; -j bzip2; -J xz; -v verbose; -C <dir>

tar -czf - src/ | ssh server 'tar -xzf - -C /srv/app'

zip -r out.zip <paths>

Create a zip archive recursively.

-r recurse; -9 max compression; -e encrypt; -j junk paths

zip -r9 build-$(date +%Y%m%d).zip dist/

unzip [-d <dir>] file.zip

Extract a zip archive, optionally to a target directory.

-d target dir; -o overwrite; -l list; -p to stdout; -q quiet

unzip -o build.zip -d ./extracted

Disk & Storage

df -h

Show mounted filesystem disk space usage, human-readable.

-h human; -T print filesystem type; -i inodes

df -hT /

du -sh <path>

Estimate file space usage; -s summarizes a directory.

-s summarize; -h human; -a all; --max-depth=N; -x stay on one fs

du -sh node_modules/ build/ .

Shell Built-ins

history / !! / !$

Browse, replay and re-use previous commands.

history N; !<n> rerun line N; !$ = last arg of last command; !! rerun last

git add . && git commit -m "$(!!)"

alias / unalias

Define or list shell command shortcuts (often in ~/.bashrc / ~/.zshrc).

alias ll='ls -lah' && alias gs='git status'

env / export / unset

List, set and clear environment variables for child processes.

export DATABASE_URL=postgres://localhost/dev && env | grep DATABASE

Help

man <cmd> / <cmd> --help

Read the manual page (man) or built-in help for a command.

man -k keyword search; man -t <cmd> print to PDF; --help short usage

man -k 'tar archive'

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About the Linux / POSIX shell

The shell is the command interpreter that turns keystrokes into operating-system actions on every Unix-like system — Linux, macOS, BSD, and the WSL on Windows. The most common shells today are bash (the GNU Bourne-again shell, default on most Linux distros, current line 5.2+), zsh (default on modern macOS since Catalina), and the POSIX-conforming dash / ash that power many embedded Linuxes. The shell exposes a powerful pipeline of small commands — `grep`, `awk`, `sed`, `find`, `xargs`, `sort`, `uniq`, `tee` — and a scripting language with variables, control flow, functions, and process substitution. The Linux shell follows the POSIX 1003.1 standard, which keeps scripts portable across distros when you stick to POSIX features rather than bash-isms. Use the shell for one-off file processing, system administration, build automation, and writing portable scripts; reach for `xargs -0` (not bare `xargs`) when filenames may contain spaces, and always quote `"$var"` to defeat word-splitting. The shell is local: nothing you type leaves your machine unless a command you run explicitly does so (such as `curl` or `ssh`).

Cheatsheet version 1.0.0