I am a data scientist and regularly refer to various file types when writing to others.

My question is this: what is the correct and/or proper way to refer to a file type and which of the following sentences is correct?

"Here is the .csv you asked for."


"Here is the CSV you asked for."

Note: .csv/CSV is used as an example only; this could be any file type (i.e. .pdf/PDF, .xlsx/XLSX). I have also excluded the word "file" from the sentence simply because it isn't the focus of my question. My question is asking how best to represent file types in writing. In this context, the other words in the sentence are irrelevant.

  • Well, did they say, "send me a dot see ess vee file" or did they say, "send me a see ess vee"? :-) – Jim Apr 13 '19 at 5:10
  • I'm not a native speaker, so take this with a grain of salt, but personally, I'd say "the CSV file" without the period but with the word "file". Without "file", it doesn't sound right. Stilted. – Mr Lister Apr 13 '19 at 6:17
  • It's a matter of style. There is no single correct way of writing it. Different people express it differently. – Jason Bassford Apr 13 '19 at 7:09
  • I, personally, would not use the dot except in very rare circumstances. I would type "Send it as a CSV" if I knew the person I was writing to or emailing was really familiar with CSV files but might use "Send it to me as a CSV file" if I was less sure of their level of knowledge (though I'd need to check they could create one). The only time I would use the dot would be if I was using an old version of software like MS Office, where I might say "I'm still using Office 2000, send it to me as a .xls not a .xlsx". Note the use of 'a' rather than 'an' because '.' is read as 'dot' – BoldBen Apr 13 '19 at 9:18
  • 1
    The form I see most often is CSV. Many people now use operating systems that hide the file extensions, so the “.” doesn’t have the meaning that it once had. It’s an evolution in the language, in the same way that ‘bus and ‘phone lost their apostrophes after people stopped thinking of them as abbreviations for omnibus and telephone. – Global Charm Apr 13 '19 at 18:15

A file type is a type of file. It would be like asking if this sentence is correct:

Here is the blue you asked for.

We are obviously missing the direct object noun (phrase), for example:

Here is the blue pen you asked for.

You could or should therefore simply add "file" to your sentences, such as:

Here is the .csv file you asked for.

I would say it is best to include the dot except for well-known extensions, where perhaps the audience has already begun to forget that there ever was a dot, such as with PDF or JPG, which in fact act as standalone nouns now:

Here is the PDF you asked for.

Here is the JPEG you asked for.

Note that some particularly ignorant writers might double down on the noun phrase in these examples, as is common with vulgar abbreviations:

Here is the JPEG picture you asked for. [Think: "ATM machine"; the .jpeg/.jpg extension already tells us the file is an image type]

NOW, if you are specifying the file extension, then since you are already being exacting with your language, it would make sense to further include the dot as well, all lowercase (convention, not rule), such as:

Here is the picture you asked for, in .jpg and .png formats for your convenience.

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