Introduction

This is a small bash handbook with examples. I made it just for fun, practice and not forget the bash basics..

Content

• Stream
• Redirections
• Lists of Commands
• Pipe
• Expansion
  • Brace
  • Parameter
• Variables
• Arrays
• Arguments
• Arithmetic
• Conditional
  • Expressions
  • Statements
• Loops
• Functions
• Exit
• Builtins
• Commands

Stream

These are three standard streams that are established when a Linux command is executed.

Code	Descriptor	Description
0	stdin	The standard input.
1	stdout	The standard output.
2	stderr	The errors output.

Redirections

Operator	Description
<	Redirecting Input
>	Redirecting Output
[&>][>&][>word 2>&1]	Redirecting Standard Output and Standard Error
>>	Appending Redirected Output
[&>>][>>word 2>&1]	Appending Standard Output and Standard Error
<<	Here Documents
<<<	Here Strings

# Redirecting Output
$ ls > /dev/stdout

# Redirecting Standard Output and Standard Error
$ ls &> /dev/stdout 
$ ls > /dev/stdout 2>&1
$ ls 2>&1 > /dev/stdout

# Here Documents  
$ cat >&2 <<END_USAGE
main: Cheat Sheet Bash Script

USAGE:
	main.sh [FLAGS] 

FLAGS:
	-h, --help				  Prints help information 

END_USAGE


# Here Strings  
string="This is a string of words."

read -r -a Words <<< "$string" 

echo "First word in String is:    ${Words[0]}"   # This
echo "Second word in String is:   ${Words[1]}"   # is
echo "Third word in String is:    ${Words[2]}"   # a
echo "Fourth word in String is:   ${Words[3]}"   # string
echo "Fifth word in String is:    ${Words[4]}"   # of
echo "Sixth word in String is:    ${Words[5]}"   # words.
echo "Seventh word in String is:  ${Words[6]}"   # (null)

Lists of Commands

    # command2 is executed if, and only if, command1 returns an exit status of zero (success).
    command1 && command2

    # command2 is executed if, and only if, command1 returns a non-zero exit status.
    command1 || command2

Pipe

The Pipe is a command in Linux that lets you use two or more commands such that output of one command serves as input to the next.

   ls -al | grep ".sh"

Also see

• Bash Reference Manual
• The Linux Documentation Project
• bash-hackers
• Google Shell Style Guide