Read binary file as string in Ruby

Question

I need an easy way to take a tar file and convert it into a string (and vice versa). Is there a way to do this in Ruby? My best attempt was this:

file = File.open("path-to-file.tar.gz")
contents = ""
file.each {|line|
  contents << line
}

I thought that would be enough to convert it to a string, but then when I try to write it back out like this...

newFile = File.open("test.tar.gz", "w")
newFile.write(contents)

It isn't the same file. Doing ls -l shows the files are of different sizes, although they are pretty close (and opening the file reveals most of the contents intact). Is there a small mistake I'm making or an entirely different (but workable) way to accomplish this?

That's a gzipped tar file (I hope). There are no "lines". Pls clarify what you're trying to achieve. — Brent.Longborough
– Brent.Longborough, Commented Sep 25, 2008 at 1:26
are you trying to look at the compressed data or uncompressed content? — David Nehme
– David Nehme, Commented Sep 25, 2008 at 1:48
so chars in a compressed data stream will have roughly 1 in 256 chance of landing on "\n" defining end of a line, and that's ok if it doesn't expect "\r" too, see my answer below — Purfideas
– Purfideas, Commented Sep 25, 2008 at 1:53
This question should be re-titled as "Convert binary file to string", since IO.read would be the preferred answer otherwise. — Ian
– Ian, Commented Nov 12, 2014 at 17:44

Rory O'Kane · Accepted Answer · 2012-07-10 07:57:31Z

403

First, you should open the file as a binary file. Then you can read the entire file in, in one command.

file = File.open("path-to-file.tar.gz", "rb")
contents = file.read

That will get you the entire file in a string.

After that, you probably want to file.close. If you don’t do that, file won’t be closed until it is garbage-collected, so it would be a slight waste of system resources while it is open.

edited Jul 10, 2012 at 7:57

Rory O'Kane

30.7k11 gold badges101 silver badges133 bronze badges

answered Sep 25, 2008 at 1:30

David Nehme

21.7k8 gold badges82 silver badges123 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

Daniel Huckstep Over a year ago

The binary flag is only relevant on Windows, and this leaves the file descriptor open. File.read(...) is better.

masterxilo Over a year ago

Is there anything wrong with so many people looking this up and copy pasting it as a one-liner solution (like so many things on stackoverflow)? After all, it works, and the name for these functions were just an arbitrary choice of the ruby library designers. If only we had some language with synonyms... that still somehow knows exactly what we want in edge cases/ambiguous instances. Then I would just contents = (contents of file "path to file.txt" as string).

shadowbq Over a year ago

This should be done in begin {..open..} ensure {..close..} end blocks

Matthew Read Over a year ago

@ArianFaurtosh No, it's another method of reading the file -- it doesn't mean that it will be treated as an exectuable and run! That would be a horrifying side-effect for a simple 'read' method.

vas Over a year ago

@David couldn't you simply do the following one-liner? contents = File.binread('path-to-file.tar.gz') See apidock. File is a subclass of IO.

|

Curt Sampson · Accepted Answer · 2008-11-07 05:24:54Z

249

If you need binary mode, you'll need to do it the hard way:

s = File.open(filename, 'rb') { |f| f.read }

If not, shorter and sweeter is:

s = IO.read(filename)

answered Nov 7, 2008 at 5:24

Curt Sampson

2 Comments

jrochkind Over a year ago

In ruby 1.9.3+, IO.read will give you a string marked with the encoding in Encoding.default_external. I think (?) the bytes will all be as they were in the file, so it's not exactly "not binary-safe", but you'll have to tag it with the binary encoding if that's what you want.

Epigene Over a year ago

If shortness and sweetness is of the essence, the ampersand-symbol proc trick gives s = File.open(filename, 'rb', &:read)

Aaron Hinni · Accepted Answer · 2008-09-25 02:02:43Z

117

To avoid leaving the file open, it is best to pass a block to File.open. This way, the file will be closed after the block executes.

contents = File.open('path-to-file.tar.gz', 'rb') { |f| f.read }

answered Sep 25, 2008 at 2:02

Aaron Hinni

14.8k6 gold badges42 silver badges39 bronze badges

1 Comment

Jeff McCune Over a year ago

This is a better answer than David Nehme's because file descriptors are a finite system resource and exhausting them is a common problem that can easily be avoided.

bardzo · Accepted Answer · 2015-06-12 09:02:07Z

21

Ruby have binary reading

data = IO.binread(path/filaname)

or if less than Ruby 1.9.2

data = IO.read(path/file)

answered Jun 12, 2015 at 9:02

bardzo

3153 silver badges6 bronze badges

1 Comment

David Moles Over a year ago

This is the correct answer for Ruby 1.9.2+.

Stu Thompson · Accepted Answer · 2011-07-27 11:39:29Z

17

how about some open/close safety.

string = File.open('file.txt', 'rb') { |file| file.read }

edited Jul 27, 2011 at 11:39

Stu Thompson

39k19 gold badges112 silver badges156 bronze badges

answered Dec 30, 2010 at 18:21

Alex

5,9692 gold badges38 silver badges25 bronze badges

3 Comments

Joshua Over a year ago

why not an explicit .close? Such as in the OP file.close when done?

Alex Over a year ago

File.open() {|file| block} automatically closes when the block terminates. ruby-doc.org/core-1.9.3/File.html#method-c-open

Abe Voelker Over a year ago

This is identical to Aaron Hinni's answer that was posted in 2008 (except not using OP's file and variable names)...

Purfideas · Accepted Answer · 2008-09-25 01:27:34Z

16

on os x these are the same for me... could this maybe be extra "\r" in windows?

in any case you may be better of with:

contents = File.read("e.tgz")
newFile = File.open("ee.tgz", "w")
newFile.write(contents)

answered Sep 25, 2008 at 1:27

Purfideas

3,2881 gold badge26 silver badges17 bronze badges

1 Comment

Dishcandanty Over a year ago

This seems like the most simple solution.

comctrl6 · Accepted Answer · 2008-09-25 01:27:05Z

6

You can probably encode the tar file in Base64. Base 64 will give you a pure ASCII representation of the file that you can store in a plain text file. Then you can retrieve the tar file by decoding the text back.

You do something like:

require 'base64'

file_contents = Base64.encode64(tar_file_data)

Have look at the Base64 Rubydocs to get a better idea.

answered Sep 25, 2008 at 1:27

comctrl6

1 Comment

Chris Bunch Over a year ago

Great, this looks like it'll work too! I'll have to check it out if for some reason reading the binary contents goes sour.

David Moles · Accepted Answer · 2021-04-28 18:26:12Z

4

Ruby 1.9+ has IO.binread (see @bardzo's answer) and also supports passing the encoding as an option to IO.read:

Ruby 1.9

data = File.read(name, {:encoding => 'BINARY'})

Ruby 2+

data = File.read(name, encoding: 'BINARY')

(Note in both cases that 'BINARY' is an alias for 'ASCII-8BIT'.)

answered Apr 28, 2021 at 18:26

David Moles

51.7k30 gold badges152 silver badges248 bronze badges

Comments

Joshua Pinter · Accepted Answer · 2015-05-14 16:09:43Z

-2

If you can encode the tar file by Base64 (and storing it in a plain text file) you can use

File.open("my_tar.txt").each {|line| puts line}

or

File.new("name_file.txt", "r").each {|line| puts line}

to print each (text) line in the cmd.

edited May 14, 2015 at 16:09

Joshua Pinter

47.9k23 gold badges261 silver badges258 bronze badges

answered Nov 24, 2014 at 11:31

Boris

711 silver badge11 bronze badges

Collectives™ on Stack Overflow

Read binary file as string in Ruby

9 Answers 9

7 Comments

2 Comments

1 Comment

1 Comment

3 Comments

1 Comment

1 Comment

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

9 Answers 9

7 Comments

2 Comments

1 Comment

1 Comment

3 Comments

1 Comment

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related