Shells provide four types of control instructions as given below:  

• Sequence Control Instruction: This ASSURES that a program's command RUNS in the sequence they are listed. As SOON as the first command in the sequence has been completed, the second command follows, and so on.
• Decision Control Instruction: It is also known as Selection Control Instruction. This instructs the computer which instruction it should execute next. In this, checking a condition is the basis for deciding which section to execute. If a given condition is True, a statement or set of STATEMENTS will be executed; otherwise, they will be ignored.
• Loop Control Instruction: It is also known as Repetition Instruction. This instruction allows a computer to continuously run a particular sequence of code. In a loop structure, the statements can be repeated until a condition is True or False, a particular number of times, or once for each element within the collection
• Case-Control Instruction: This is used for selecting among several CHOICES. Typically, they are used to execute only a particular block of statements within a series of statements.