Dash Shell Scripting Cheatsheet

Dash Fundamentals

Comments	`# This is a comment`
Variables	`variable=value` `echo $variable`
String literals	`'Single quoted'` `"Double quoted"`
Command Substitution	`$(command)` or `command`
Exit Status	`$?` (Exit status of last command)
Shebang	`#!/bin/sh` (Specifies the interpreter)

`if` statement	`if [ condition ]; then # commands fi`
`if-else` statement	`if [ condition ]; then # commands else # commands fi`
`if-elif-else` statement	`if [ condition ]; then # commands elif [ condition ]; then # commands else # commands fi`
`case` statement	`case $variable in pattern1) commands ;; pattern2) commands ;; *) commands ;; esac`
`while` loop	`while [ condition ]; do # commands done`
`until` loop	`until [ condition ]; do # commands done`

`ls`	List directory contents
`cp`	Copy files or directories
`mv`	Move or rename files or directories
`rm`	Remove files or directories
`mkdir`	Create directories
`touch`	Create an empty file or update timestamp

`echo`	Display a line of text
`cat`	Concatenate and display files
`grep`	Search for a pattern in files
`sed`	Stream editor for text manipulation
`awk`	Pattern scanning and processing language
`wc`	Word, line, and byte count

`uname`	Print system information
`date`	Print or set the system date and time
`pwd`	Print working directory
`whoami`	Print effective userid
`uptime`	Show how long the system has been running
`free`	Display amount of free and used memory

`+`	Addition
`-`	Subtraction
`*`	Multiplication
`/`	Division
`%`	Modulo
`**`	Exponentiation (not POSIX standard, may not work on all shells)

`-e file`	True if file exists
`-f file`	True if file exists and is a regular file
`-d file`	True if file exists and is a directory
`-r file`	True if file exists and is readable
`-w file`	True if file exists and is writable
`-x file`	True if file exists and is executable

function function_name {
  # commands
}

# or

function_name () {
  # commands
}

Example:

my_function() {
  echo "Hello, world!"
}

my_function

Accessing arguments	`$1`, `$2`, … `$n`
All arguments	`$@`
Number of arguments	`$#`
Example	`my_function() { echo "First argument: $1" echo "Second argument: $2" } my_function "arg1" "arg2"`

Executing a script	`./script.sh # or sh script.sh`
Making a script executable	`chmod +x script.sh`
Sourcing a script	`. script.sh # or source script.sh`
Differences between executing and sourcing	Executing runs in a subshell, sourcing runs in the current shell.