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Is there an in-built function in Ruby to read the whole file without using any loop? So far, I have only come across methods that read in chunks (line or character).

Shubham
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    For what it's worth, this is something that people often want but don't really need. (And if the file is very large, you can get a nasty surprise when file slurping gobbles near all your available memory.) What are you ultimately trying to accomplish? – Telemachus Jul 25 '10 at 12:00
  • I found this very helpful for working with a file that was not in an every day format. I was reading a file in IBM437 coding and needed to break the file at the oddball characters, to separate the valuable data from the stuff I did not need. For that it made sense to read the entire file and then create my own line breaks where they should be. Otherwise I'd be passing in each line or each character. Instead I could simply use this to read the file, and then use split to break the file at strings of printable characters, and then use a block to determine the sets of data that I need. – ndw Mar 29 '13 at 22:15
  • I'd recommend reading http://stackoverflow.com/questions/25189262/why-is-slurping-a-file-bad. – the Tin Man Dec 15 '16 at 17:41

3 Answers3

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IO.read("filename")

or

File.read("filename")
sluukkonen
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    Just out of curiousity, why can't I find this function here: http://www.ruby-doc.org/core-2.1.2/File.html – Martin Konecny Jun 19 '14 at 20:10
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    @MartinKonecny because `File::read` is actually inherited from `IO::read` - they both are exactly the same because `File` extends `IO`. – Moshe Katz Aug 19 '14 at 03:22
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File.readlines("filename")

This is also a great method to read everything from a file and break split on carriage returns. The return is an Array with one line per element.

Nick
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    More specifically, `readlines` splits on the internal variable `$/`, which defaults to "\n". You can temporarily reset `$/`, however, and read files into chunks delimited in other ways, too. – Telemachus Jul 25 '10 at 12:32
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Please ignore advice which states "You should never slurp (which is the annoying term for this) a file". Sometimes this is a very useful, and sensible thing to do.

Suppose you're reading a file repeatedly : good chance that reading the file into an array is a sensible optimisation over reading the file line by line, even taking into account that the o/s will cache the file.

Graham Nicholls
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    This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient [reputation](http://stackoverflow.com/help/whats-reputation) you will be able to [comment on any post](http://stackoverflow.com/help/privileges/comment). - [From Review](/review/low-quality-posts/10916920) – ndnenkov Jan 17 '16 at 02:32
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    Sorry, but simply not interested in working up a rep. The advice to "not slurp" is just plain wrong. It is sometimes a useful technique (I've just reduced the runtime of a program by a factor of 1000 by reading the whole file), and should not be deprecated. – Graham Nicholls Jan 18 '16 at 08:36
  • Reading a file into memory in one pass (slurping) isn't any faster than line-by-line once a file hits 1MB+ in size. Beyond that point you can read line-by-line faster, and avoid potential scalability problems. "just plain wrong" isn't helpful without explaining when it is appropriate. See http://stackoverflow.com/questions/25189262/why-is-slurping-a-file-bad for more information. – the Tin Man Dec 15 '16 at 17:45
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    Well I think I gave an example - you're repeatedly reading the file. Useful to have it in an array. I've (been paid to) program in more than 20 languages, so suspect that I have some insight. I'm dogmatic on some things (comments ARE a code-smell), but not on this one. Use it when it makes the code more readable, or the solution simpler to grasp. Don't use it if it is very sub-optimal, or makes the solution more complex. And I reiterate my point re a reputation. I'll leave that to the amateurs trying to gain points for their CVs. – Graham Nicholls Dec 31 '16 at 11:21