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Shell Script To Check the String For a Particular Condition

  • Last Updated : 14 Sep, 2021

Here, we are going to write a shell script that will echo (print) a suitable message if the accepted string does not meet a particular condition. Suppose we have given some certain conditions then our task is to print the message if the accepted string doesn’t match the condition.

Example 1: 

If the accepted string’s length is smaller than 10, we will display a message saying “String is too short“.

Input:  "abcdef"
Output:  String is too short
Length is 6, which is smaller than 10.

Approach:

  • We will take a string from the user
  • We have to find the length of the string so that we can decide whether it is smaller or larger than 10.
  • We will find the length using the following command:
len=`echo -n $str | wc -c`

Below is the Implementation:



# Shell script to print message 
# when condition doesn't matched

# taking user input
echo "Enter the String : "
read string

# Finding the length of string 
# -n flag to avoid new line
# wc -c count the chars in a file
len=`echo -n $string | wc -c`

# Checking if length is smaller
# than 10 or not
if [ $len -lt 10 ]
    then
        # if length is smaller 
        # print this message
        echo "String is too short."
fi

Output:

Example 2: We will accept two input String and find whether both are equal or not.

String1 -> a = “abc”

String2 -> b = “abc”

Here a and b are equal.

Below is the implementation:

# Shell script to check whether two 
# input strings is equal

# take user input
echo "Enter string a : "
read a

echo "Enter string b : "
read b

# check equality of input
if [ "$a" = "$b" ]; then

    # if equal print equal
    echo "Strings are equal."
else
      # if not equal
    echo "Strings are not equal."
fi

Output:

Geeks
Geeks
Strings are equal.

Example 3:

We are working with strings, so now we will take two strings as input and check which of the two is greater in respect of lexicographical (alphabetical) order.

string1 > string2 : The greater than operator returns true if the left operand is greater than the right sorted by lexicographical (alphabetical) order.

string1 < string2 : The less than operator returns true if the right operand is greater than the right sorted by lexicographical (alphabetical) order.

# Shell script to check which 
# string is lexicographically
# larger

# user input
echo "Enter String a : "
read a

echo "Enter String b : "
read b

# if a is greater than b
if [[ "$a" > "$b" ]]; then
    echo "${a} is lexicographically greater then ${b}."

# if b is greater than a
elif [[ "$a" < "$b" ]]; then
    echo "${b} is lexicographically greater than ${a}."

# if both are equal
else
    echo "Strings are equal"
fi

Output:

abc
def
def is lexicographically greater than abc.
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