# Newbie question on file reading
**URL:** https://rubytalk.org/t/newbie-question-on-file-reading/59763
**Category:** ruby-talk
**Created:** [24 August 2010 11:04 UTC](https://rubytalk.org/t/newbie-question-on-file-reading/59763 "2010-08-24T11:04:12Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@Rajarshi\_Chakravarty](https://rubytalk.org/u/Rajarshi_Chakravarty)
#### Post date: [24 August 2010 11:04 UTC](https://rubytalk.org/t/newbie-question-on-file-reading/59763/1 "2010-08-24T11:04:12Z")
Hi,
I have got the code to read a file line by line amd it works too but I
don't understand it.
fp = File.open(dataFile, "r")
fp.each\_line do |line|
puts line
end
My question is: the "open" method is not mentioned in the doc of File
class
[http://ruby-doc.org/core/classes/File.html](http://ruby-doc.org/core/classes/File.html)
What type does it return?
My 2nd question is how can I read a file char by char. Basically the
file doesn't have line breaks.
Please help..
> **···**
>
> --
> Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/).
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### Author:  [@Peter\_Hickman2](https://rubytalk.org/u/Peter_Hickman2)
#### Post date: [24 August 2010 11:11 UTC](https://rubytalk.org/t/newbie-question-on-file-reading/59763/2 "2010-08-24T11:11:03Z")
I believe it comes from the IO class instead
[http://ruby-doc.org/core/classes/IO.html](http://ruby-doc.org/core/classes/IO.html)
---
### Author:  [@Martin\_DeMello](https://rubytalk.org/u/Martin_DeMello)
#### Post date: [24 August 2010 13:39 UTC](https://rubytalk.org/t/newbie-question-on-file-reading/59763/3 "2010-08-24T13:39:17Z")
How big is your file? IO.read("/path/to/file") will read the entire
file into a string. If you really want to read it character by
character
File.open("/path/to/file") do |f|
while true do
begin
a = f.readchar
# do something with a
rescue EOFError
break
end
end
end
martin
> **···**
>
> On Tue, Aug 24, 2010 at 4:34 PM, Rajarshi Chakravarty \ wrote:
>
> > My 2nd question is how can I read a file char by char. Basically the
> > file doesn't have line breaks.
---
### Author:  [@Robert\_K1](https://rubytalk.org/u/Robert_K1)
#### Post date: [24 August 2010 13:12 UTC](https://rubytalk.org/t/newbie-question-on-file-reading/59763/4 "2010-08-24T13:12:09Z")
Yes, this is true.
Rajarshi, you can make your life a bit simpler by doing
File.foreach(dataFile) do |line|
puts line
end
If you actually need to open the file and manipulate the File / IO
object directly (e.g. because you want to rewind), you can use the
block form of File.open (or IO.open):
File.open(dataFile, "r") do |fp|
fp.each\_line do |line|
puts line
end
end
This ensures the file is properly closed which was not the case in
your original example. You can find more at
[http://blog.rubybestpractices.com/posts/rklemme/001-Using\_blocks\_for\_Robustness.html](http://blog.rubybestpractices.com/posts/rklemme/001-Using_blocks_for_Robustness.html)
And if you want to know the internal workings you can look here
[http://blog.rubybestpractices.com/posts/rklemme/002\_Writing\_Block\_Methods.html](http://blog.rubybestpractices.com/posts/rklemme/002_Writing_Block_Methods.html)
Kind regards
robert
> **···**
>
> 2010/8/24 Peter Hickman \:
>
> > I believe it comes from the IO class instead
> > [class IO - RDoc Documentation](http://ruby-doc.org/core/classes/IO.html)
>
> --
> remember.guy do |as, often| as.you\_can - without end
> [http://blog.rubybestpractices.com/](http://blog.rubybestpractices.com/)
---
### Author:  [@Rajarshi\_Chakravarty](https://rubytalk.org/u/Rajarshi_Chakravarty)
#### Post date: [24 August 2010 13:41 UTC](https://rubytalk.org/t/newbie-question-on-file-reading/59763/5 "2010-08-24T13:41:28Z")
Thank you, Robert.
The links were most helpful.
I need to read char substrings from a file that has no line breaks in
it.
Is the code below the best way to do it?
File.foreach(dataFile) do |line|
puts line
end
Will the "line" var give the entire text in the file?
Another question (this is posted on the link you gave)
Instead of doing File.foreach(dataFile) can I not do
IO.foreach(dataFile) do |line|?
> **···**
>
> --
> Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/).
---
### Author:  [@Robert\_K1](https://rubytalk.org/u/Robert_K1)
#### Post date: [24 August 2010 14:08 UTC](https://rubytalk.org/t/newbie-question-on-file-reading/59763/6 "2010-08-24T14:08:22Z")
> Thank you, Robert.
Your welcome!
> The links were most helpful.
Good!
> I need to read char substrings from a file that has no line breaks in
> it.
Note that you can use a different separator character:
File.foreach data\_file, "SEPARATOR" do |entry|
puts entry
end
The same works for File.each:
File.open... do |io|
io.each "SEPARATOR" do |entry|
...
end
end
> Is the code below the best way to do it?
>
> File.foreach(dataFile) do |line|
> puts line
> end
>
> Will the "line" var give the entire text in the file?
No, because this will try to load lines separated by \n. If you want
the whole text of the file in one go you can do
contents = File.read data\_file
However, if the file is large, a blocked approach usually yields better results:
File.open data\_file do |io|
buffer = ""
while io.read(1024, buffer)
buffer.each\_char {|ch| p ch} # note, ch is really a String of length 1
end
end
> Another question (this is posted on the link you gave)
> Instead of doing File.foreach(dataFile) can I not do
> IO.foreach(dataFile) do |line|?
Yes, File and IO are interchangeable here. Personally I prefer to use
File when dealing with files just for documentation reasons.
Kind regards
robert
> **···**
>
> 2010/8/24 Rajarshi Chakravarty \:
>
> --
> remember.guy do |as, often| as.you\_can - without end
> [http://blog.rubybestpractices.com/](http://blog.rubybestpractices.com/)
---
### Author:  [@Rajarshi\_Chakravarty](https://rubytalk.org/u/Rajarshi_Chakravarty)
#### Post date: [24 August 2010 18:53 UTC](https://rubytalk.org/t/newbie-question-on-file-reading/59763/7 "2010-08-24T18:53:38Z")
Thank you, Martin and Robert
> **···**
>
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> Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/).
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### Author:  [@Rajarshi\_Chakravarty](https://rubytalk.org/u/Rajarshi_Chakravarty)
#### Post date: [26 August 2010 08:44 UTC](https://rubytalk.org/t/newbie-question-on-file-reading/59763/8 "2010-08-26T08:44:48Z")
In continuation with my questions about reading files from the file
system...
It seems Dir[File.join(root, subDir, "\*")] gives the full path name of
all files in the sub directory
Can I modify the expression to give just the basename?
> **···**
>
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> Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/).
---
### Author:  [@Robert\_K1](https://rubytalk.org/u/Robert_K1)
#### Post date: [26 August 2010 08:58 UTC](https://rubytalk.org/t/newbie-question-on-file-reading/59763/9 "2010-08-26T08:58:29Z")
You can feed the result through #map and File.basename.
Cheers
robert
> **···**
>
> 2010/8/26 Rajarshi Chakravarty \:
>
> > In continuation with my questions about reading files from the file
> > system...
> >
> > It seems Dir[File.join(root, subDir, "\*")] gives the full path name of
> > all files in the sub directory
> >
> > Can I modify the expression to give just the basename?
>
> --
> remember.guy do |as, often| as.you\_can - without end
> [http://blog.rubybestpractices.com/](http://blog.rubybestpractices.com/)