Ruby get file extension from string

Ruby Get File Extension from String

Sometimes developer requires to extract only file extension from the string object. File class can be used to perform this operation. We will see how to use File class to get the extension name.

Let's create a sample string with Filename. Suppose we have a file with name "ruby-in-rails-logo.jpg" and string object as,

filename = "ruby-in-rails-logo.jpg"

of which extension ".jpg" we want for some check in the program. Then we can use File class as follows,
Solution

Use method File.extname as follows,
Syntax:

file_extension = File.extname(filename)
=> ".jpg"

Method File#extname when passed string with filename then it returns extension of that file. In above example it is .jpg
You can read source page of File#extname on APIDock for the C source code of this method.
Sample Conversions

File.extname("ruby/in/rails/logo.jpg")
=> ".jpg"

File.extname("ruby-in-rails-logo")
=> ""
# as there is no extension in the string passed as filename

File.extname(".ruby-in-rails-logo")
""
# As not valid extension length, refer APIDock source for more on this.


What Not to do

Sometimes, idea may come to mind to extract filename from the string yourself using split method as follows,

filename = "ruby-in-rails-logo.jpg"
extension = filename.split(".").last
=> "jpg"

Which will return result as "jpg" for you which is also the required result for your program. But the C level implementation for the File#extname is more suitable considering performance. Thus, using File#extname is advised.