Ubuntu – How to convert the perl index script to bash function

I want to use perl to get the index of from any given string and substring in bash function.

Here is the example for getting the indexOf value from perl script:

https://www.geeksforgeeks.org/perl-index-function/

#!/usr/bin/perl
 
# String from which Substring 
# is to be searched 
$string = "Geeks are the best";
 
# Using index() to search for substring
$index = index ($string, 'the');
 
# Printing the position of the substring
print "Position of 'the' in the string: $indexn";

Output:

Position of 'the' in the string: 10

Here is the test.sh:

#!/bin/bash

bash_function_get_index_from_perl_script() {
    local index="-1"
    
    # Here is the dummy code 
    # as I don't know how to convert
    # the perl script to bash command lines
    # and get the result from perl script
    
    index="
    
        #!/usr/bin/perl
         
        # String from which Substring 
        # is to be searched 
        $string = "Geeks are the best";
         
        # Using index() to search for substring
        $index = index ($string, 'the');
         
        # Printing the position of the substring
        print "Position of 'the' in the string: $indexn";
    
    "
    
    printf "%s" "$index"
}

result="$(bash_function_get_index_from_perl_script)"

echo "result is: $result"

Here is the expected output:

result is: 10

How to implement the "bash_function_get_index_from_perl_script"?

Update:

Here is the bash function for testing:

#!/bin/bash

bash_function_get_index() {
    local string="$1"
    local search_string="$2"
    
    before=${string%${search_string}*}
    index=${#before}
    
    printf "%s" "$index"
}

echo "test 1: $(bash_function_get_index "hello world" "wo")"
echo "test 2: $(bash_function_get_index "hello world" "wox")"

Here is the output:

test 1: 6
test 2: 11

The result of "test 2" is wrong, it should be:

test 2: -1

I want to implement the same "indexOf" function from Java:

https://www.w3schools.com/java/ref_string_indexof.asp

index_of() {
    local string="$1"
    local search_string="$2"
    local fromIndex="$3"
    
    local index=""
    
    # Get the real index here, the result shoule be the same as the Java's "indexOf"
        
    printf "%s" "$index"
}