How to Check if String Contains a Substring in Bash

1. Use the case Conditional Statement (Method 1)
2. Use Wildcards in the if Statement (Method 2)
3. Use the grep Command of Bash (Method 3)
4. Use the Regex Operator (~=) (Method 4)

Finding substring from a string is the most frequently used operation with strings. There are many ways to perform this task.

In this article, we will see multiple Bash script-based implementations to find if a given string contains a particular substring or not.

Use the case Conditional Statement (Method 1)

The case is a conditional statement in bash and can be used to implement a conditional block in the script. This statement can be used to find a substring in bash.

Script:

#!/bin/bash

str='This is a bash tutorial'
substr='bash'

case $str in

  *"$substr"*)
    echo  "str contains the substr"
    ;;
esac

We have 2 strings, str and substr. We have applied a case statement to find if str contains substr or not.

Output:

Use Wildcards in the if Statement (Method 2)

We can also find a substring from a string using wildcards in the if statement. The simplest way to find a substring is by putting the wildcard symbol asterisk (*) around the substring and comparing it with the actual string.

Script:

#!/bin/bash

str='This is a bash tutorial'
substr='tutorial'
if [[ "$str" == *"$substr"* ]]; then
  echo "String contains the sunstring"
else
  echo "String does'nt contains the substring"
fi

Output:

Use the grep Command of Bash (Method 3)

grep command is also used to find something from a file or a string. It has an option -q, which tells the grep command to not display the output; return true or false.

Script:

#!/bin/bash

str='This is a bash tutorial'
substr='tutorial'
if grep -q "$substr" <<< "$str"; then
  echo "String contains the substring"
fi

Output:

Use the Regex Operator (~=) (Method 4)

There is another operator known as regex operator (~=) with which we can compare two strings and whether a string contains a substring.

Script:

#!/bin/bash

str='This is a bash tutorial'
substr='bash'
if [[ "$str" =~ .*"$substr".* ]]; then
  echo "String contains the substring"
fi

Note that in the conditional statement, the regex operator makes the right-hand side string a regular expression and the symbol .* means to compare 0 or more occurrences of a substring in the string.

Output:

Hence, you can see several ways to find a substring from a string.