bash
name='Jonathan'Notes
Do not put spaces around = in shell assignment.
Bash Variables, Quoting, and Expansion
Bash variables, parameter expansion, quoting rules, command substitution, arithmetic, and shell expansion patterns.
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Variables
Assign, export, inspect, and unset variables.
bash
echo "$name"Notes
Double quotes preserve spaces and most characters.
bash
export APP_ENV=productionNotes
Needed when subprocesses should receive the value.
bash
unset nameNotes
Useful for cleanup and testing default expansion behavior.
Default value expansion
Use a fallback if variable is unset or empty.
bashANYparameter-expansiondefaults
bash
echo "${PORT:-3000}"Notes
One of the most common parameter expansion patterns.
Assign default value
Assign default if variable is unset or empty.
bashANYparameter-expansiondefaults
bash
echo "${PORT:=3000}"Notes
Be careful because this mutates the variable.
Require variable
Abort expansion with error if variable is missing.
bashANYparameter-expansionvalidation
bash
echo "${DATABASE_URL:?DATABASE_URL is required}"Notes
Great for defensive scripts and deployment checks.
Alternate value expansion
Use alternate text when variable is set and non-empty.
bashANYparameter-expansionconditional
bash
echo "${DEBUG:+enabled}"Notes
Good for optional flags and output labels.
Quoting
Single quotes, double quotes, escaping, and ANSI-C quoting.
bash
echo 'Path is $HOME'Notes
Use when you need literal shell characters.
Expandable double-quoted string
Double quotes allow variable and command expansion.
bashANYquotesexpansion
bash
echo "Path is $HOME"Notes
Usually the safest choice around variable expansions.
bash
echo "A quote: \""Notes
Needed when embedding quotes in strings.
bash
printf '%s
' $'line1
line2'Notes
Bash supports $'...' expansion for escaped literals.
bash
echo '\$HOME'Notes
Handy when writing examples or templates.
Parameter and Command Expansion
Substring, replacement, command substitution, and arithmetic.
bash
today=$(date +%F)Notes
Prefer $(...) over backticks for clarity and nesting.
bash
echo $((2 + 3 * 4))Notes
Useful for counters, lengths, and simple math.
bash
echo "${#name}"Notes
Works for strings and arrays.
bash
echo "${name:0:4}"Notes
Offsets are zero-based.
bash
echo "${file/.txt/.bak}"Notes
Useful for filename transforms.
bash
echo "${path//\//:}"Notes
The doubled slash means global replacement.
bash
echo "${path#*/}"Notes
Handy for path processing.
bash
echo "${file%%.*}"Notes
Useful for basename-like operations and extensions.
Globbing and Brace Expansion
Filename matching and brace generation.
bash
printf '%s
' *.txtNotes
Globs are expanded by the shell before command execution.
bash
printf '%s
' file-{a,b,c}.txtNotes
Brace expansion happens before pathname expansion.
bash
printf '%s
' {1..5}Notes
Great for loops and quick test data.
bash
shopt -s nullglobNotes
Safer than leaving a literal pattern in loops.
bash
shopt -s dotglobNotes
Useful for file moves and maintenance tasks.
More in Bash
Bash Scripting Patterns and Practical Recipes
Production-minded Bash script patterns for files, arguments, parsing, temp files, logging, retries, and common automation tasks.
Bash Builtins, Job Control, and Shell Behavior
Core Bash builtins, shell options, history, aliases, job control, traps, and interactive-shell behavior.
Bash Arrays, Strings, and Text Handling
Indexed and associative arrays, string handling, read/mapfile, and common Bash text-processing patterns.
Bash Conditionals, Loops, and Functions
Bash if/elif/case logic, test expressions, loops, functions, return codes, and robust control-flow patterns.
Bash Cheat Sheet
Comprehensive Bash commands, shell syntax, quoting, variables, redirection, pipelines, and day-to-day scripting patterns.
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