Module-8 How to use select statement in bash scripting

Table of contents

• Introduction
• Select statement syntax
• Practical example on select statement used in bash script
• Using the select statement with arrays instead of the direct string
• How to use select statement along with the case statement to execute a block of the statements

Introduction

Select statements are used to build a menu from the input values like array or  strings, etc. 

It waits for inputs , we can provide the inputs by using the menu item number as prompted and then it  assigns that menu item to a variable and executes other lines of codes. It won’t exit after one set of execution as it works like a loop , it waits for another input to execute the same set of codes again assigning new value to the variable . We had to ctrl +c to exit the code. 

In this Article we will see how to use the select statements in the bash scripting

Select statement syntax 

select item in < strings or array expansion >
do 
   <other code block>
 done 

Practical example on select statement used in bash script

In the following script example 

Step1 : we feeded the select statement with set of strings to create the menu 

Step2 : when we selected one of the menu item , that is assigned to the variable item and used in the further lines of the code 

Step3 : it prompts for inputs again 

Step4 : to exit we need hit ctrl + c

#script 
[root@discoveringsystems select-statement]# cat select-statement-script
#!/bin/bash


echo " Select one of the options available"

select item in apple orange banana grapefruit

do
  echo " the selected fruit is $item "

done

#script execution
[root@discoveringsystems select-statement]# ./select-statement-script
 Select one of the options available
1) apple
2) orange
3) banana
4) grapefruit
#? 1
 the selected fruit is apple
#? 3
 the selected fruit is banana
#? ^C
[root@discoveringsystems select-statement]#

Using the select statement with arrays instead of the direct string 

In this example , we did the same like before , but this time we were using the arrays in place of set of strings 

#script
[root@discoveringsystems select-statement]# cat select-statement-script
#!/bin/bash


echo " Select one of the options available"

array=('apple' 'orange' 'banana' 'grapefruit')

select item in ${array[@]}

do
  echo " the selected fruit is $item "

done

#script execution
[root@discoveringsystems select-statement]# ./select-statement-script
 Select one of the options available
1) apple
2) orange
3) banana
4) grapefruit
#? 1
 the selected fruit is apple
#? 3
 the selected fruit is banana
#? ^C

How to use select statement along with the case statement to execute a block of code

We know that it required ctrl + c to exit the select statement used in the scripts , so we incorporated the case statement with an option to help exit the select statement without hitting the ctrl +c , but through other inputs 

If you are new to case statement , please go through our other article on how to use case statements for more clarity 

How to use case statements in bash scripts

Step1: Same array is used to feed the menu items in the select statement 

Step2: User input creates a variable called item due to select statement 

Step3 : This variable is used in the case statement to select one option and execute the block of codes 

Step4 : one such option is executing the break statement to exit the select statement loop 

#script 
[root@discoveringsystems select-statement]# cat select-statement-script-2
#!/bin/bash


echo " select the username from the list "

array=('alice' 'bob' 'charlie' 'exit')

select item in ${array[@]}

do


  case $item in

    Alice | alice)
      echo "Welcome Alice ! you role is network admin "
      ;;

    Bob | bob)
      echo "Welcome Bob ! your role is network operator "
      ;;

    Charlie | charlie)
      echo " Welcome Charlie ! your role is general operator "
      ;;

    exit | Exit)
      echo " exiting as per user request "
      break
      ;;

    *)
      echo " Entered value is incorrect , please re-enter the correct value "
      ;;

  esac
done

#script execution 
[root@discoveringsystems select-statement]# ./select-statement-script-2
 select the username from the list
1) alice
2) bob
3) charlie
4) exit
#? 2
Welcome Bob ! your role is network operator
#? 4
 exiting as per user request