RoR: Handling Blanks AND/OR Special Characters - ruby-on-rails

Question

I'm processing emails for upload and occasionally an embedded image in the email comes through either without a file extension or with an extension containing a random combination of letters, numbers and special characters (for example: image001.gif#01CFA02B.47556390). If either instance arrives, I want to ignore it and move on. I think I've got the without extension covered, but wasn't clear on how best to handle the random characters and well as the cleanest way in to write the conditionals. Here is what I have so far:
filename_extension = File.extname(filename)
if filename_extension.blank?
puts "FILENAME EXT IS BLANK"
elsif filename_extension #NEED REGEX or something to handle Random?
puts "FILENAME EXT IS Random"
else #DO PROCESSING
Thanks.

Answer 1

known_extensions = %w[.csv .rb .rbw .html .htm .css]
filenames = %w[1.txt 2.csv 3]
filenames.each do |filename|
filename_extension = File.extname(filename)
if filename_extension.empty?
puts "FILENAME EXT IS BLANK"
elsif known_extensions.include? filename_extension
puts "FILENAME EXT IS Random"
else #DO PROCESSING
puts "Processing"
end
end
The question was tagged ruby without any indicate of gems that may give you the blank? method.
The idea of an 'invalid' extension is rather varied, and of course tied to what it means to be a valid file name. On most Unix file systems, for example, the only limitations on an file name would the limitation of the filename size of 255 bytes, and the reserved characters of / and null. In fact, there is no specification that I am aware of about 'extensions' in Unix, as they are simply a part of a file name, the period in a file name being valid, not signifying anything special. (With the exception of a file name that starts with a period indicating that it should be a 'hidden' file.) On a Windows system, it is a longer list of characters, some of which are / : < > ? \ | + , . ; = [ ] as well as the single and double quotes. On my Commodore, I think it was :, , and =, and on my Amiga system I could use anything except for ", :, or /.
So I think 'invalid' extension might be easier to match than the 'valid' ones. If you are indeed using Rails, and hosting on Unix, then you have a smaller set of things to check for, to ensure a valid extension (indeed, a valid filename). Basing that invalid extension on your hosting system, and any restrictions you would place due to your idea of what a valid extension means to your program.