One of the most common operations when working with strings in Bash is to determine whether or not a string contains another string.

In this article, we will show you several ways to check if a string contains a substring.

Using Wildcards

The easiest approach is to surround the substring with asterisk wildcard symbols (asterisk) * and compare it with the string. Wildcard is a symbol used to represent zero, one or more characters.

If the test returns true, the substring is contained in the string.

In the example below we are using the if statement and the equality operator (==) to check whether the substring SUB is found within the string STR:

#!/bin/bash

STR='GNU/Linux is an operating system'
SUB='Linux'
if [[ "$STR" == *"$SUB"* ]]; then
  echo "It's there."
fi

Copy

When executed the script will output:

It's there.

Using the case operator

Instead of using the if statement you can also use the case statement to check whether or not a string includes another string.

#!/bin/bash

STR='GNU/Linux is an operating system'
SUB='Linux'

case $STR in

  *"$SUB"*)
    echo -n "It's there."
    ;;
esac

Copy

Using Regex Operator

Another option to determine whether a specified substring occurs within a string is to use the regex operator =~. 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='GNU/Linux is an operating system'
SUB='Linux'

if [[ "$STR" =~ .*"$SUB".* ]]; then
  echo "It's there."
fi

Copy

The script will echo the following:

It's there.

#string #linux #java #javascript