How to use Conditional Statements on Bash Script

To Use Conditional Statements On Bash Script

Introduction:

The conditional statement is used in any programming language to do any decision-making tasks. This statement is also used in bash to perform automated tasks like another programming language, just the syntax is a little bit different in bash. Bash using two types of conditional statements.

Installation Steps:

Step1: Check the Oracle Linux Version by using the below command

[root@linuxhelp ~]# cat /etc/os-release
NAME="Oracle Linux Server"
VERSION="9.2"
ID="ol"
ID_LIKE="fedora"
VARIANT="Server"
VARIANT_ID="server"
VERSION_ID="9.2"
PLATFORM_ID="platform:el9"
PRETTY_NAME="Oracle Linux Server 9.2"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:oracle:linux:9:2:server"
HOME_URL="https://linux.oracle.com/"
BUG_REPORT_URL="https://github.com/oracle/oracle-linux"
ORACLE_BUGZILLA_PRODUCT="Oracle Linux 9"
ORACLE_BUGZILLA_PRODUCT_VERSION=9.2
ORACLE_SUPPORT_PRODUCT="Oracle Linux"
ORACLE_SUPPORT_PRODUCT_VERSION=9.2

Step 2: Next create one script file for if Condition by using Vim command

[root@linuxhelp ~]# vim ifscript
#!/bin/bash
read -p " Enter number : " number
if [ $number -eq 100 ]  ## if the condition is true then run the condition
then
echo "Value is equal to  100"
fi

Step 3: To execute the script first change the executable file permission by using the following command

[root@linuxhelp ~]# chmod +x ifscript

Step 4: To list the file by using the following commands

[root@linuxhelp ~]# ll

total 8
-rw-r--r--. 1 root root    0 Sep 13 11:40 100
-rw-------. 1 root root 1062 Sep  4 17:37 anaconda-ks.cfg
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Desktop
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Documents
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Downloads
-rwxr-xr-x. 1 root root  176 Sep 13 12:34 ifscript
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Music
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Pictures
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Public
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Templates
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Videos

Step 5: To execute the script by using the following command

[root@linuxhelp ~]# ./ifscript
 Enter number : 100
Value is equal to  100

Step 6: Again, execute the script by using the following command, if the conditions is not true

[root@linuxhelp ~]# ./ifscript
Enter number : 44
[root@linuxhelp ~]#

Step 7: Next create a one script file for if else Condition by using Vim command

[root@linuxhelp ~]# vim ifelse
#!/bin/bash
echo -n "Enter a number: "
read VAR
if [[ $VAR -gt 10 ]]
then
  echo "The variable is greater than 10."
else
  echo "The variable is equal or less than 10."
fi

Step 8: To execute the script first change the executable file permission by using the following command

[root@linuxhelp ~]# chmod +x ifelse

Step 9: To list the file by using the following commands

[root@linuxhelp ~]# ll
total 12
-rw-r--r--. 1 root root    0 Sep 13 11:40 100
-rw-------. 1 root root 1062 Sep  4 17:37 anaconda-ks.cfg
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Desktop
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Documents
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Downloads
-rwxr-xr-x. 1 root root  175 Sep 13 15:09 ifelse
-rwxr-xr-x. 1 root root  176 Sep 13 12:34 ifscript
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Music
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Pictures
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Public
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Templates
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Videos

Step 10: To execute the script by using the following command. If the first condition is true, it will be the output

[root@linuxhelp ~]# ./ifelse
Enter a number: 40
The variable is greater than 10.

Step 11: Again, execute the script by using the following command. If condition is false, it will be the output

[root@linuxhelp ~]# ./ifelse
Enter a number: 2
The variable is equal or less than 10.

Step 12: Next create a one script file for if elif Condition by using Vim command

[root@linuxhelp ~]# vim ifelif
#!/bin/bash
echo -n "Enter a number: "
read VAR
if [[ $VAR -gt 10 ]]
then
  echo "The variable is greater than 10."
elif [[ $VAR -eq 10 ]]
then
  echo "The variable is equal to 10."
else
  echo "The variable is less than 10."
fi

Step 13: To execute the script first change the executable file permission by using the following command

[root@linuxhelp ~]# chmod +x ifelif

Step 14: To list the file by using the following commands

[root@linuxhelp ~]# ll
total 24
-rw-r--r--. 1 root root  175 Sep 13 15:12 @
-rw-r--r--. 1 root root    0 Sep 13 11:40 100
-rw-------. 1 root root 1062 Sep  4 17:37 anaconda-ks.cfg
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Desktop
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Documents
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Downloads
-rwxr-xr-x. 1 root root  232 Sep 13 15:47 ifelif
-rwxr-xr-x. 1 root root  175 Sep 13 15:09 ifelse
-rwxr-xr-x. 1 root root  176 Sep 13 12:34 ifscript
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Music
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Pictures
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Public
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Templates
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Videos

Step 15: To execute the script by using the following command. If the first condition is true, it will be the output

[root@linuxhelp ~]# ./ifelif
Enter a number: 100
The variable is greater than 10.

Step 16: To execute the script by using the following command. If the Second condition is true, it will be the output

[root@linuxhelp ~]# ./ifelif
Enter a number: 10
The variable is equal to 10.

Step 17: To execute the script by using the following command. If the first and second condition is false, it will be the output

[root@linuxhelp ~]# ./ifelif
Enter a number: 5
The variable is less than 10.

Step 18: Next create a one script file for Nested if Condition by using Vim command

[root@linuxhelp ~]# vim nestedif
#!/bin/bash
echo -n "Enter the first number: "
read VAR1
echo -n "Enter the second number: "
read VAR2
echo -n "Enter the third number: "
read VAR3
if [[ $VAR1 -ge $VAR2 ]]
then
  if [[ $VAR1 -ge $VAR3 ]]
  then
    echo "$VAR1 is the largest number."
  else
    echo "$VAR3 is the largest number."
  fi
else
  if [[ $VAR2 -ge $VAR3 ]]
  then
    echo "$VAR2 is the largest number."
  else
    echo "$VAR3 is the largest number."
  fi
fi

Step 19: To execute the script first change the executable file permission by using the following command

[root@linuxhelp ~]# chmod +x nestedif

Step 20: To list the file by using the following commands

[root@linuxhelp ~]# ll
total 24
-rw-r--r--. 1 root root  175 Sep 13 15:12 @
-rw-r--r--. 1 root root    0 Sep 13 11:40 100
-rw-------. 1 root root 1062 Sep  4 17:37 anaconda-ks.cfg
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Desktop
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Documents
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Downloads
-rwxr-xr-x. 1 root root  232 Sep 13 15:47 ifelif
-rwxr-xr-x. 1 root root  175 Sep 13 15:09 ifelse
-rwxr-xr-x. 1 root root  176 Sep 13 12:34 ifscript
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Music
-rwxr-xr-x. 1 root root  440 Sep 13 16:16 nestedif
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Pictures
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Public
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Templates
drwxr-xr-x. 2 root root    6 Sep 13 11:36 Videos

Step 21: To execute the script by using the following command

[root@linuxhelp ~]# ./nestedif 
Enter the first number:10
Enter the second number:15 
Enter the Thied number:20
20 is the largest number:

Conclusion:

We have reached the end of this article. In this guide, we have walked you through the steps required to use Conditional Statements on Bash Script (if elif nestedif). Your feedback is much welcome.