Ruby - Creating a file in memory

Question

Is there anyway to write the following code in Ruby without writing the file to disk?

temp_file = 'path/to/file.csv'
users = [a@b.c, c@b.a]

CSV.open(temp_file, "w") do |csv|
  csv << data_for_report
end

Reports.sendreport users temp_file

File.delete(temp_file)

The Reports.sendreport attaches a file and sends an email, so it needs to be a file...

So you want a string of comma separated values? Do you need the csv at that point? Could you join your columns with commas, and your rows with newlines? — quandrum, Jan 23 '13 at 20:31
Ohh, the sendreport function sends a mail with a csv-file attached. So I really need it to be a file... — hirolau, Jan 23 '13 at 20:37
Are you saying the sendreport method reads the file from disk? — quandrum, Jan 23 '13 at 20:52
Correct.. It reads a file from disc and attaches it to an email. The question now is if there is anyway to save the file, as a file, in memory. — hirolau, Jan 23 '13 at 21:02
If you can't change `Reports`, then you probably are doing it the right way. It's probably more trouble than it's worth to get a section of memory to pretend it's a disk so `Reports` can read from it. — quandrum, Jan 23 '13 at 21:25

score 20 · Answer 1 · edited Feb 25 '14 at 21:17

20

You could use Tempfile. Tempfile writes the file to disc, so it does not fit your request.

But I think Tempfile provides some features you need:

When a Tempfile object is garbage collected, or when the Ruby interpreter exits, its associated temporary file is automatically deleted.

Example:

require 'tempfile'
require 'csv'

data_for_report = [1,2,3,4]
temp_file = Tempfile.new('foo')

CSV.open(temp_file, "w") do |csv|
  csv << data_for_report
end

edited Feb 25 '14 at 21:17

answered Jan 23 '13 at 21:47

knut

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It is one step closer.. Thank you! – hirolau Jan 23 '13 at 22:14
Note that it's `Tempfile`, not `TempFile`. – GMA Jan 08 '14 at 05:56
The link to Ruby doc is broken – vovan Aug 08 '19 at 09:15

score 4 · Answer 2 · answered Sep 04 '19 at 21:10

4

temp_file = CSV.generate do |csv|
  csv << data_for_report
end

Reports.sendreport users temp_file

answered Sep 04 '19 at 21:10

Gregory Ray

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This is the correct answer to the question `Is there anyway to write the following code in Ruby without writing the file to disk?` Other answers seems to be workarounds (tempfiles) – Greg Mar 30 '23 at 10:53

score 3 · Answer 3 · answered Jan 07 '19 at 15:00

With your current code that's not possible, if your code would use file pointers/handles instead you can do the following:

require 'csv'
require 'stringio'

data_for_report = [1,2,3,4]
temp_file = StringIO.new # creates a fake file as string.

CSV.new(temp_file, "w") do |csv|
  csv << data_for_report
end

The key problem why it isn't working for your usecase is the line Reports.report users temp_file

If that accepts a handle instead of a string it'll work.

See also this SO: https://stackoverflow.com/a/19110958/887836

score 2 · Accepted Answer · answered Jan 23 '13 at 21:12

2

Try one of the mmap gems. If the library only takes a filename, that's your option.

If it can accept a file-like object, however, you can use a StringIO.

You might consider changing whatever Reports is, making it more general-purpose. It depends on what it's using to create its mail message–this might be trivial.

answered Jan 23 '13 at 21:12

Dave Newton

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I will look into StringIO, think that might be what I am looking for... Reports.sendreport is really just my own wrapper on the gmail gem, so I am not really sure if i need a real if or if StringIO will work. – hirolau Jan 23 '13 at 22:13

Ruby - Creating a file in memory

4 Answers4

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