bash
Synopsis
Bash is a powerful scripting language that is used by many developers. This cheat sheet is a collection of Bash tips and tricks that will help you write better Bash scripts.
Bash Basics
| Command | Description |
|---|
echo | Print a message to the console |
printf | Print a formatted message to the console |
cat | Print the contents of a file to the console |
pwd | Print the current working directory |
cd | Change the current working directory |
ls | List the contents of a directory |
mkdir | Create a new directory |
touch | Create a new file |
cp | Copy a file or directory |
mv | Move a file or directory |
rm | Remove a file or directory |
find | Find files or directories |
grep | Search for a string in a file |
wc | Count the number of lines, words, and characters in a file |
sort | Sort the lines in a file |
uniq | Remove duplicate lines in a file |
head | Print the first 10 lines of a file |
tail | Print the last 10 lines of a file |
man | Display the manual page for a command |
which | Display the location of a command |
type | Display the type of a command |
alias | Create an alias for a command |
history | Display the command history |
clear | Clear the console |
exit | Exit the console |
Variables
| Command | Description |
|---|
var="value" | Assign a value to a variable |
echo $var | Print the value of a variable |
echo ${var} | Print the value of a variable |
echo "$var" | Print the value of a variable |
echo "${var}" | Print the value of a variable |
echo '$var' | Print the literal value of a variable |
echo '${var}' | Print the literal value of a variable |
echo "${var:-default}" | Print the value of a variable or a default value if the variable is not set |
echo "${var:=default}" | Assign a default value to a variable if the variable is not set |
echo "${var:?error}" | Print an error message if the variable is not set |
echo "${var:+value}" | Print a value if the variable is set |
echo "${var:offset}" | Print a substring of a variable |
Functions
| Command | Description |
|---|
function_name() { ... } | Define a function |
function_name() { echo "Hello World"; } | Define a function |
function_name() { echo "Hello $1"; } | Define a function with parameters |
function_name() { echo "Hello $@"; } | Define a function with parameters |
Arrays
| Command | Description |
|---|
array=(value1 value2 value3) | Define an array |
echo ${array[0]} | Print the value of an array element |
echo ${array[@]} | Print the values of an array |
echo ${#array[@]} | Print the number of elements in an array |
echo ${#array[0]} | Print the length of an array element |
array[0]="value" | Assign a value to an array element |
array+=(value) | Append a value to an array |
unset array[0] | Remove an array element |
unset array | Remove an array |
Conditionals
| Command | Description |
|---|
if [ condition ]; then ... fi | If statement |
if [ condition ]; then ... else ... fi | If/else statement |
if [ condition1 ]; then ... elif [ condition2 ]; then ... else ... fi | If/elif/else statement |
case value in pattern1) ... ;; pattern2) ... ;; esac | Case statement |
case value in pattern1) ... ;; pattern2) ... ;; *) ... ;; esac | Case statement with a default case |
Loops
| Command | Description |
|---|
for var in value1 value2 value3; do ... done | For loop |
for var in $(command); do ... done | For loop |
for (( i=0; i<10; i++ )); do ... done | For loop |
while [ condition ]; do ... done | While loop |
until [ condition ]; do ... done | Until loop |
| Command | Description |
|---|
read var | Read input from the console |
read -p "Enter a value: " var | Read input from the console with a prompt |
read -a array | Read input from the console into an array |
read -d | Read input from the console until a delimiter is found |
read -s | Read input from the console without echoing the input |
read -n | Read a specified number of characters from the console |
read -t | Read input from the console with a timeout |
echo "Hello World" > file.txt | Redirect output to a file |
echo "Hello World" >> file.txt | Append output to a file |
echo "Hello World" 2> file.txt | Redirect error output to a file |
Debugging
| Command | Description |
|---|
set -x | Enable debugging |
set +x | Disable debugging |
set -v | Print shell input lines as they are read |
set +v | Do not print shell input lines as they are read |
set -n | Read commands but do not execute them |
set +n | Execute commands read from the command line |
Miscellaneous
| Command | Description |
|---|
echo "Hello World" | Print a string |
echo -n "Hello World" | Print a string without a newline |
echo -e "Hello\tWorld" | Print a string with escaped characters |
Bash Advanced
Bash Builtins
| Command | Description |
|---|
. | Execute a script in the current shell |
source | Execute a script in the current shell |
: | Do nothing |
true | Do nothing |
false | Do nothing |
break | Exit a loop |
continue | Skip to the next iteration of a loop |
return | Exit a function |
exit | Exit the shell |
set | Set shell options |
unset | Unset shell options |
export | Export a variable |
readonly | Make a variable read-only |
declare | Declare a variable |
typeset | Declare a variable |
local | Declare a local variable |
eval | Evaluate a string as a command |
exec | Execute a command |
shift | Shift positional parameters |
wait | Wait for a background process to complete |
pwd | Print the current working directory |
cd | Change the current working directory |
pushd | Push the current working directory onto the directory stack |
Bash Options
| Command | Description |
|---|
set -o | List shell options |
set -o noclobber | Do not overwrite existing files |
set -o errexit | Exit on error |
set -o errtrace | Exit on error in a function |
set -o nounset | Exit on unset variable |
set -o pipefail | Exit on pipe failure |
set -o xtrace | Print commands and their arguments as they are executed |
Bash Aliases
| Command | Description |
|---|
alias | List aliases |
alias name="command" | Create an alias |
unalias | Remove an alias |
Bash Functions
| Command | Description |
|---|
function name { ... } | Define a function |
name() { ... } | Define a function |
declare -f | List functions |
declare -f name | List a function |
Bash Arrays
| Command | Description |
|---|
array=(value1 value2 value3) | Create an array |
array[0]="value" | Assign a value to an array element |
array+=(value) | Append a value to an array |
unset array[0] | Remove an array element |
unset array | Remove an array |
declare -a | List arrays |
declare -a array | List an array |
declare -p | List variables |
declare -p array | List a variable |
Bash Conditionals
| Command | Description |
| -------------------------------- | ------------ | -------------- | ------------ |
| [[ condition ]] | If statement |
| [[ condition1 && condition2 ]] | If statement |
| [[ condition1 | | condition2 ]] | If statement |
| [[ ! condition ]] | If statement |
| [[ value1 == value2 ]] | If statement |
| [[ value1 != value2 ]] | If statement |
| [[ value1 < value2 ]] | If statement |
| [[ value1 > value2 ]] | If statement |
Bash Loops
| Command | Description |
|---|
for var in "${array[@]}"; do ... done | For loop |
for (( i=0; i<10; i++ )); do ... done | For loop |
while [[ condition ]]; do ... done | While loop |
until [[ condition ]]; do ... done | Until loop |
select var in "${array[@]}"; do ... done | Select loop |
| Command | Description |
|---|
read -p "Enter a value: " value | Read input from the console |
read -p "Enter a value: " -s value | Read input from the console without echoing the input |
read -p "Enter a value: " -n 5 value | Read a specified number of characters from the console |
Bash Arguments
| Command | Description |
|---|
$# | Specifies number of arguments |
$* | Specifies all positional arguments as a single word |
$@ | Specifies all positional arguments as separate words |
$1 | Specifies first argument passed |
$_ | Specifies last argument of the previous command |