How to Check if a String Contains a Substring in Bash

While you working with string in Bash need to check whether a string contains another string. In this guide, we will show you multiple ways to check if a string contains a substring in bash scripting.

Use Wildcards#

It is easy to use asterisk wildcard symbols (asterisk) * to compare with the string. Wildcard is a symbol used to represent zero, one or more characters. If the string contained the string it will returns true.

Let’s see an example, we are using if statement with equality operator (==) to check whether the substring SUBSTR is found within the string STR:

#!/bin/bash

STR='Ubuntu is a Linux OS'
SUBSTR='Linux'
if [[ "$STR" == *"$SUBSTR"* ]]; then
  echo "String is there."
fi

It will show following output:

String is there.

Use the case operator#

You can use the case statement instead of if statement to check whether a string includes or not to another string.

#!/bin/bash

STR='Ubuntu is a Linux OS'
SUBSTR='Linux'

case $STR in

  *"$SUBSTR"*)
    echo -n "String is there."
    ;;
esac

Using Regex Operator#

Another way is to use the regex operator =~ to check whether a specified substring occurs within a string. When this operator is used, the right string is considered as a regular expression.

The period followed by an asterisk .* matches zero or more occurrences any character except a newline character.

#!/bin/bash

STR='Ubuntu is a Linux OS'
SUBSTR='Linux'

if [[ "$STR" =~ .*"$SUBSTR".* ]]; then
  echo "String is there"
fi

The script will echo the following:

String is there

Using Grep#

The grep command can also be used to find strings in another string.

In the below example, we are giving string in the $STR variable to grep and check if the string $SUBSTR is found within the string. It will return true or false.

#!/bin/bash

STR='Ubuntu is a Linux OS'
SUBSTR='Linux'

if grep -q "$SUB" <<< "$STR"; then
  echo "String is there"
fi

Conclusion#

In this article, you learned how to check a substring contains in the given string using multiple ways in Bash script.

If you have any questions or feedback, feel free to leave a comment.