Bash scripting cheat sheet

Variables, tests, for/while loops and functions: the core Bash syntax for writing a reliable script.

Free Updated on September 11, 2026

Variables

name="Ana"                   # no space around the =
echo "Hello $name"           # use the variable
readonly PI=3.14              # constant
unset name                    # remove a variable

Conditions

if [ "$age" -ge 18 ]; then
    echo "adult"
elif [ "$age" -ge 13 ]; then
    echo "teenager"
else
    echo "child"
fi

Test	Meaning
`-eq` `-ne`	equal / not equal (numbers)
`-lt` `-le` `-gt` `-ge`	<, <=, >, >= (numbers)
`=` `!=`	equal / not equal (strings)
`-z` `-n`	string is empty / non-empty
`-f` `-d`	file exists / directory exists

Loops

for f in *.txt; do
    echo "Processing $f"
done

for i in {1..5}; do echo $i; done

while read -r line; do
    echo "$line"
done < file.txt

Functions and arguments

greet() {
    echo "Hello $1"
}
greet "Ana"

echo "Script: $0, first argument: $1, all: $@, count: $#"

Always quote variables ("$variable") to avoid surprises with values containing spaces or empty strings. set -euo pipefail at the top of a script turns errors loud instead of silent.

Variables

Conditions

Loops

Functions and arguments

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