bash
name='alice'Notes
Do not put spaces around `=` in shell variable assignments.
Linux Shell Scripting Cheat Sheet
High-value Linux shell scripting reference covering variables, expansion, conditionals, loops, functions, redirection, pipelines, traps, getopts, and script debugging.
Export
Copy the compact sheet, download it, or print it.
Download
`D` dense toggle · `C` copy all
Variables and Expansion
Define shell variables, expand strings, and work safely with parameters.
bash
export APP_ENV=productionNotes
Used for config values consumed by child commands and scripts.
Use default value if unset
Expand parameter with a fallback.
bashLINUXshellparameter-expansiondefaults
bash
echo "${PORT:-8080}"Notes
Useful in scripts where environment variables may be optional.
Require variable to be set
Fail fast if a variable is missing.
bashLINUXshellparameter-expansionvalidation
bash
echo "${DATABASE_URL:?DATABASE_URL is required}"Notes
Great for scripts that should stop immediately when config is missing.
bash
files=$(find . -type f | wc -l)Notes
Use `$(...)` instead of legacy backticks.
bash
printf '%s
' "$name"Notes
Double-quote variable expansions unless you intentionally want word splitting.
Conditionals Loops and Functions
Build shell scripts that branch, loop, and encapsulate logic.
bash
if [[ -f /etc/app.conf ]]; then echo 'exists'; fiNotes
Common script pattern for optional config files.
bash
if [[ -d releases ]]; then ls releases; fiNotes
Useful for deployment and housekeeping scripts.
bash
for f in *.log; do echo "$f"; doneNotes
Quote variables inside the loop body to handle spaces safely.
bash
while IFS= read -r line; do echo "$line"; done < input.txtNotes
Preferred pattern for preserving whitespace and backslashes.
bash
case "$1" in start) echo start ;; stop) echo stop ;; *) echo usage ;; esacNotes
Cleaner than long `if/elif` chains for command dispatch.
bash
greet() { echo "hello $1"; }Notes
Functions help keep scripts readable and avoid repetition.
bash
set -euo pipefailNotes
Widely used hardening pattern for production shell scripts.
bash
trap 'rm -f "$tmpfile"' EXITNotes
Useful for temporary files, locks, and service teardown in scripts.
Input Output and Pipelines
Redirect streams, build pipelines, and control output files.
bash
echo 'hello' > greeting.txtNotes
Use `>>` to append instead of overwrite.
bash
echo 'next line' >> app.logNotes
Common for quick logging in scripts.
bash
command 2> errors.logNotes
Useful when preserving errors separately from normal output.
bash
command > command.log 2>&1Notes
Common logging pattern in scripts and cron jobs.
Pipe stdout to another command
Send output of one command as input to another.
bashLINUXshellpipeunix
bash
ps aux | grep nginxNotes
Pipelines are the foundation of Unix composition.
Use process substitution
Pass command output as a pseudo-file.
bashLINUXshellprocess-substitutiondiff
bash
diff <(sort old.txt) <(sort new.txt)Notes
Handy when a command expects file arguments but you want to compare pipeline output.
bash
read -rp 'Enter environment: ' envNotes
Useful for operator-driven scripts and local helpers.
Print formatted output
Use printf instead of echo for predictable formatting.
bashLINUXshellprintfformat
bash
printf 'user=%s id=%s
' "$USER" "$UID"Notes
Preferred in scripts because format control is explicit.
Script Execution and Utilities
Run scripts, parse arguments, and debug shell behavior.
bash
#!/usr/bin/env bashNotes
Portable way to locate Bash on many systems.
bash
chmod +x deploy.shNotes
Then run it directly as `./deploy.sh`.
bash
./deploy.shNotes
Use an explicit path so the shell does not rely on `PATH`.
bash
bash -x ./deploy.shNotes
Very useful for debugging shell scripts and CI tasks.
bash
while getopts ':f:n:' opt; do case "$opt" in f) file="$OPTARG" ;; n) count="$OPTARG" ;; esac; doneNotes
Useful for small production scripts with predictable CLI flags.
bash
shellcheck deploy.shNotes
One of the highest-value tools for improving script quality.
More in Linux
Linux Permissions and Security Cheat Sheet
High-value Linux permissions and security reference covering users, sudo, ACLs, special mode bits, SSH access, SELinux, and AppArmor basics.
Linux Networking Admin Cheat Sheet
Comprehensive Linux networking administration reference covering iproute2, DNS, HTTP debugging, TLS, SSH tunnels, packet capture, and firewall inspection.
Linux Package Management Cheat Sheet
Comprehensive Linux package management reference for apt, dnf, yum, pacman, zypper, rpm, and dpkg workflows across common distributions.
Linux Command Cheat Sheet
Comprehensive Linux command reference covering navigation, files, text processing, permissions, processes, system information, networking, archives, services, storage, and troubleshooting.
Recommended next
Bash Scripting Patterns and Practical Recipes
BASH
Production-minded Bash script patterns for files, arguments, parsing, temp files, logging, retries, and common automation tasks.
Bash Builtins, Job Control, and Shell Behavior
BASH
Core Bash builtins, shell options, history, aliases, job control, traps, and interactive-shell behavior.
Bash Arrays, Strings, and Text Handling
BASH
Indexed and associative arrays, string handling, read/mapfile, and common Bash text-processing patterns.
Bash Conditionals, Loops, and Functions
BASH
Bash if/elif/case logic, test expressions, loops, functions, return codes, and robust control-flow patterns.
Bash Variables, Quoting, and Expansion
BASH
Bash variables, parameter expansion, quoting rules, command substitution, arithmetic, and shell expansion patterns.
Bash Cheat Sheet
BASH
Comprehensive Bash commands, shell syntax, quoting, variables, redirection, pipelines, and day-to-day scripting patterns.