Bash Scripting Cheat Sheet

Interactive Bash scripting reference with variables, loops, conditions, functions, arrays, and string operations. Searchable examples. Free, no signup required.

Variables

Declare variable

name="Alice"
age=30

Read-only variable

readonly PI=3.14159

Unset variable

unset name

Default value

${var:-default}   # use default if var unset
${var:=default}   # assign default if var unset
${var:?error msg} # error if var unset

String length

${#str}

Substring

${str:offset:length}  # e.g. ${str:2:4}

Uppercase / Lowercase

${str^^}  # uppercase
${str,,}  # lowercase

String Operations

Concatenation

full="$first $last"

Remove prefix

${str#prefix}   # shortest
${str##prefix}  # longest

Remove suffix

${str%suffix}   # shortest
${str%%suffix}  # longest

Replace

${str/old/new}   # first occurrence
${str//old/new}  # all occurrences

Check if contains substring

[[ "$str" == *"sub"* ]] && echo "found"

Split string

IFS="," read -ra arr <<< "$csv"

Arrays

Declare array

arr=(one two three)
declare -a arr

Access element

${arr[0]}

All elements

${arr[@]}

Array length

${#arr[@]}

Append

arr+=(four)

Slice

${arr[@]:1:2}  # elements 1 and 2

Iterate

for item in "${arr[@]}"; do
  echo "$item"
done

Associative array

declare -A map
map["key"]="val"
echo ${map["key"]}

Conditionals

if / elif / else

if [ "$x" -eq 1 ]; then
  echo "one"
elif [ "$x" -eq 2 ]; then
  echo "two"
else
  echo "other"
fi

Test operators

# Numeric: -eq -ne -lt -le -gt -ge
# String:  = != -z (empty) -n (not empty)
# File:    -f -d -e -r -w -x -s

case statement

case "$opt" in
  start) echo "Starting";;
  stop)  echo "Stopping";;
  *)     echo "Unknown";;
esac

Double bracket [[ ]]

[[ "$a" =~ ^[0-9]+$ ]] && echo "numeric"

Ternary-like

[[ condition ]] && echo "yes" || echo "no"

Loops

for loop (list)

for i in 1 2 3 4 5; do
  echo "$i"
done

for loop (range)

for i in {1..10}; do echo "$i"; done
for ((i=0; i<10; i++)); do echo "$i"; done

while loop

while [ $count -gt 0 ]; do
  echo $count
  ((count--))
done

until loop

until [ $done -eq 1 ]; do
  check_condition
done

Loop over files

for f in /var/log/*.log; do
  echo "$f"
done

read lines from file

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

break / continue

break     # exit loop
continue  # skip to next iteration

Functions

Define function

greet() {
  local name="$1"
  echo "Hello, $name!"
}

Call function

greet "Alice"

Return value

add() { echo $(( $1 + $2 )); }
result=$(add 3 5)

Return exit code

is_root() {
  [ "$(id -u)" -eq 0 ]
}
is_root && echo "root"

Local variables

func() {
  local x=10  # scoped to function
}

File Tests

Test operators

-e file   # exists
-f file   # is regular file
-d dir    # is directory
-r file   # readable
-w file   # writable
-x file   # executable
-s file   # size > 0
-L file   # is symlink
f1 -nt f2 # f1 newer than f2
f1 -ot f2 # f1 older than f2

Example usage

if [ -f "/etc/nginx/nginx.conf" ]; then
  echo "nginx config exists"
fi

Special Variables

Exit status

$?   # exit code of last command (0=success)

Script PID

$$   # PID of current shell/script

Argument count

$#   # number of positional arguments

All arguments

$@   # all args as separate words
$*   # all args as single string

Script name

$0   # name of the script

Positional params

$1 $2 $3 ... # individual arguments

Last background PID

$!   # PID of last background job

IFS

$IFS  # Internal Field Separator (default: space/tab/newline)

Heredoc

Basic heredoc

cat <<EOF
This is line 1
This is line 2
EOF

Heredoc to file

cat > /etc/motd <<EOF
Welcome to my server!
EOF

Suppress tab indent

cat <<-EOF
	indented content
	EOF

No variable expansion

cat <<'EOF'
$PATH won't expand here
EOF

Process Substitution & Redirection

Redirect stdout

cmd > file.txt

Redirect stderr

cmd 2> err.txt

Both stdout & stderr

cmd > out.txt 2>&1
cmd &> all.txt

Append

cmd >> file.txt

Process substitution

diff <(sort file1) <(sort file2)

Pipe

cmd1 | cmd2 | cmd3

Named pipe (FIFO)

mkfifo mypipe
cmd1 > mypipe & cmd2 < mypipe

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A searchable, interactive reference for Bash scripting fundamentals. Quickly find syntax examples for variables, loops, functions, and string operations without leaving your browser. Perfect for developers who need fast, practical Bash answers.

How it works

1Search for Bash syntax or concepts in the searchable index
2Browse interactive examples with code snippets and explanations
3Copy working code samples directly into your scripts
4Reference common patterns for loops, functions, and conditionals

Who uses this tool

✓System administrators automating infrastructure and server tasks
✓DevOps engineers writing deployment and CI/CD pipeline scripts
✓Developers learning Bash scripting fundamentals quickly
✓Linux users creating shell scripts for file and data processing
✓Students studying command-line automation and shell programming

Frequently Asked Questions

How do I use Bash Cheat Sheet?

Browse by category (variables, loops, functions) or search for a specific syntax. Each example is runnable and copyable.

Is Bash Cheat Sheet free?

Yes, Bash Cheat Sheet on ToolPix is 100% free with no signup or installation required.

Is my data safe?

This is a static reference tool. No data is entered or transmitted.

What is the difference between sh and bash?

sh is the original POSIX shell. bash is a superset with arrays, [[]], string manipulation, and more. Use #!/bin/bash if you need bash-specific features.

How do I run a bash script?

Make it executable with chmod +x script.sh then run with ./script.sh. Or run directly with bash script.sh without needing execute permission.

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