Execute shell script:

./script.sh
bash script.sh
source script.sh

Read user input:

read

Echo text to screen:

echo

Arithmetic operations:

let
expr

Conditional statements:

if
case

Loops:

for
while

Array operations:

declare 
read -a

Check file/directory existence:

[file] -e 
[file] -d 
[file] -f

Check file permissions:

1. r
2. w
3. x

Check file type:

1. b
2. c
3. L
4. S