Question

Is there a way to open a file case-insensitively in Ruby under Linux? For example, given the string foo.txt, can I open the file FOO.txt?

One possible way would be reading all the filenames in the directory and manually search the list for the required file, but I’m looking for a more direct method.

Answer 1

One approach would be to write a little method to build a case insensitive glob for a given filename:

def ci_glob(filename)
  glob = ''
  filename.each_char do |c|
    glob += c.downcase != c.upcase ? "[#{c.downcase}#{c.upcase}]" : c
  end
  glob
end

irb(main):024:0> ci_glob('foo.txt')
=> "[fF][oO][oO].[tT][xX][tT]"

and then you can do:

filename = Dir.glob(ci_glob('foo.txt')).first

Alternatively, you can write the directory search you suggested quite concisely. e.g.

filename = Dir.glob('*').find { |f| f.downcase == 'foo.txt' }

---

Prior to Ruby 3.1 it was possible to use the FNM_CASEFOLD option to make glob case insensitive e.g.

filename = Dir.glob('foo.txt', File::FNM_CASEFOLD).first
if filename
  # use filename here
else
  # no matching file
end

The documentation suggested FNM_CASEFOLD couldn’t be used with glob but it did actually work in older Ruby versions. However, as mentioned by lildude in the comments, the behaviour has now been brought inline with the documentation and so this approach shouldn’t be used.