error while reading a text file in ruby

*file_name means variable amount of parameters, you would need to extract the first parameter with file_name[0], check the other answer for single parameter or use multiple files:

def read_file_info(*files)
  files.each do |file_name|
    arr = IO.readlines(file_name)
    puts arr
  end
end

read_file_info("abcd.txt", "efgh.txt")

Write it as:

def read_file_info(file_name)
  arr = IO.readlines(file_name)
  puts arr
end

read_file_info("abcd.txt")

This is what happened when you pass "abcd.txt" to the method. *file_name creates an array:

def read_file_info(*file_name)
  p file_name
end

read_file_info("abcd.txt")
# >> ["abcd.txt"]

IO.readlines(file_name) expects a single file name as a string, but you gave it an Array, which, in turn, gave you the error:

no implicit conversion of Array into String (TypeError)

If you want to use *file_name then, inside the method, use Array#[] to give your IO.readlines method a single file at a time as a string.