Concatenation of strings is the most common process when working with string. In Bash, you can concatenate string variables using the concatenation operator + or by simply putting them next to each other.

Without using the concatenation operator +:

str1="Hello"

str2="World"

concatenated_str=$str1$str2

echo $concatenated_str

The output will be:
HelloWorld

Using the concatenation operator +:
str1="Hello"

str2="World"

concatenated_str=$str1+$str2

echo $concatenated_str

The output will be:
HelloWorld

Note that if you want to include a space between the strings, you need to add it explicitly, like this:
str1="Hello"

str2="World"

concatenated_str="$str1 $str2"

echo $concatenated_str

The output will be:
Hello World