Looping Statements | Shell Script

Looping Statements in Shell Scripting: There are total 3 looping statements which can be used in bash programming

1. while statement
2. for statement
3. until statement

To alter the flow of loop statements, two commands are used they are,

1. break
2. continue

Their descriptions and syntax are as follows:

• while statement
  Here command is evaluated and based on the result loop will executed, if command raise to false then loop will be terminated
  Syntax

  while command
  do
     Statement to be executed
  done

• for statement
  The for loop operate on lists of items. It repeats a set of commands for every item in a list.
  Here var is the name of a variable and word1 to wordN are sequences of characters separated by spaces (words). Each time the for loop executes, the value of the variable var is set to the next word in the list of words, word1 to wordN.
  Syntax
  
  
  
  

  for var in word1 word2 ...wordn
  do
     Statement to be executed
  done

• until statement
  The until loop is executed as many as times the condition/command evaluates to false. The loop terminates when the condition/command becomes true.
  Syntax

  
  until command
  do
     Statement to be executed until command is true
  done
  

Example Programs

Example 1:
Implementing for loop with break statement

Output

$bash -f main.sh
Iteration no 1
Iteration no 2
Iteration no 3
Iteration no 4

Example 2:
Implementing for loop with continue statement

Output

$bash -f main.sh
Iteration no 1
Iteration no 2
Iteration no 3
Iteration no 4
Iteration no 6
Iteration no 7
Iteration no 8
Iteration no 9
Iteration no 10

Example 3:
Implementing while loop

Output:

$bash -f main.sh
0
1
2
3
4
5
6
7
8
9

Example 4:
Implementing until loop

Output:

$bash -f main.sh
0
1
2
3
4
5
6
7
8
9
10

Note: Shell scripting is a case-sensitive language, which means proper syntax has to be followed while writing the scripts.