Variables

Basis

myVar=myValue
Assign a value to the variable (warning, no space!).

myVar=$(whoami)
Assign command output to the variable.

$myVar
Access variable content.

Array

myArray=()
Create an empty array.

myArray=( 12 12 )
Create an array with values (note the space between values).

myArray[0]=myValue
Assign a value to the first value of the array.

myArray+=(myValue)
Append value at the end of the array (add a value).

${myArray[0]}
Return the first value of the array.

${myArray[@]}
Return the whole array.

${myArray[3:@]}
Return the values form third to last.

${#myArray[@]}
Return the array size.

Special Variables

$?
Output code of previously executed program.

$0
Path of the currently called script.

$1, $2 ...
Arguments passed to the script.

$#
Arguments numbers.

$@
Return all the arguments.

date
Return date, time, and time difference.

date "+%H"
Return the current hour. (%H = hour, %M = minute, %S = second, …).

seq 1 12
Return a number sequence.

Structures

Condition

if [ boolean ]
then
	...
elif
then
	...
else
	...
fi

For Loop

for i in `seq 0 100`
do
	...
done

for i in {1..100}
do
	...
done

directories=( myDir1 myDir2 myDir3)

for directory in "${directories[@]}"; do
	mkdir -p $directory
	...
done

While Loop

# Read lines for file
while read line
do
	echo $line
done < myFile

while read line; do echo $line; done < myFile.txt
One liner version of while loop to read file.

Redirections

Chevrons

>
Redirects to a file (if it already exists, it will be overwritten).

>>
Redirects to the end of a file (if it doesn't exist, it will be created).

2>
Redirects errors to a file (if it already exists, it will be overwritten).

2>>
Redirects errors to the end of a file (if it doesn't exist, it will be created).

2>&1
Redirects errors in the standard output.

< myFile
Sends a file as a input command.

KEYWORD <<
Switches the console to keyboard input mode, line by line. All the lines will be sent when the end keyword has been written.

<<< myString
Sends a string as a input command.

Ampersand

cmd1 & cmd2
First command will be executed in background.

cmd1 && cmd2
Second command is executed if the first command return code is 0 (ok).

Pipe

cmd1 | cmd2
Chains commands (output from command 1 is sent to command 2).

cmd1 || cmd2
Second command is executed if the first command return code is not 0 (error).