61.String_Test_Options.md

String Test Options

1. str1 = str2 → Returns true if both strings are the same
2. str1 != str2 → Returns true if both strings are different
3. -z str → Returns true if the string is empty
4. -n str → Returns true if the string is not empty
5. str1 > str2 → Returns true if str1 is alphabetically greater than str2
6. str1 < str2 → Returns true if str1 is alphabetically less than str2

Demo Program for String Comparison

Script:

#!/bin/bash
read -p "Enter First String:" str1
read -p "Enter Second String:" str2
if [ $str1 = $str2 ]; then
    echo "Both strings are equal"
elif [ $str1 \< $str2 ]; then
    echo "$str1 is less than $str2"
else
    echo "$str1 is greater than $str2"
fi

Note:

• To prevent < from being interpreted as an input redirection operator, use the backslash (\) before it.

Example Output:

Enter First String: Durga
Enter Second String: Durga
Both strings are equal

Enter First String: Apple
Enter Second String: Banana
Apple is less than Banana

Enter First String: Banana
Enter Second String: Apple
Banana is greater than Apple

Q13: Script to Check if the Login User is Root

Script:

#!/bin/bash
user=$(whoami)
if [ $user != "root" ]; then
    echo "Current user is not root and hence exiting"
    exit 1
fi

echo "The Five Current Running Processes Information"
echo "=============================================="
ps -ef | head -5

Example Output:

Current user not root user and hence exiting

# When executed as root:
The Five Current Running Processes Information
UID        PID  PPID  C STIME TTY      TIME CMD
root         1     0  0 19:32 ?        00:00:03 /sbin/init splash
root         2     0  0 19:32 ?        00:00:00 [kthreadd]
root         3     2  0 19:32 ?        00:00:00 [rcu_gp]
root         4     2  0 19:32 ?        00:00:00 [rcu_par_gp]

Q14: Script to Test if the String is Empty or Not

Script:

#!/bin/bash
read -p "Enter Any String to test:" str
if [ -z "$str" ]; then
    echo "Provided input string is empty"
else
    echo "Provided input string is not empty"
    echo "Its length is: $(echo -n "$str" | wc -c)"
fi

Case Statement

Definition:

• When multiple options are available, using nested if-else statements can make code lengthy and less readable.
• To handle such scenarios, use a case statement.

Syntax:

case $variable in
    option1 )
        action-1
        ;;
    option2 )
        action-2
        ;;
    option3 )
        action-3
        ;;
    * )
        default action
        ;;
esac

Notes:

1. Spaces around the options are optional.
2. ;; is mandatory after each option except for the default option.
3. The default option (*) can be placed anywhere in the case statement.
4. If the default option is placed at the beginning, it will be executed for any input.