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comp.lang.ruby

Ruby way to update a file in place

Li Chen

6/11/2007 7:42:00 PM

Hi all,

I just wonder what is the Ruby way to update a file in place. Do I need
to open a temporary/new file for writing and then rename the temporary
file?

Thanks,

Li

--
Posted via http://www.ruby-....
11 Answers

Daniel Berger

6/11/2007 7:55:00 PM

0

On Jun 11, 1:42 pm, Li Chen <chen_...@yahoo.com> wrote:
> Hi all,
>
> I just wonder what is the Ruby way to update a file in place. Do I need
> to open a temporary/new file for writing and then rename the temporary
> file?

That's the usual way. The other way is to use mmap.

Regards,

Dan

Joel VanderWerf

6/11/2007 8:04:00 PM

0

Li Chen wrote:
> Hi all,
>
> I just wonder what is the Ruby way to update a file in place. Do I need
> to open a temporary/new file for writing and then rename the temporary
> file?

You can open with the "r+" file mode, and use seek/rewind to move to a
position within the file, use #truncate to end the file, and so on.

[~/tmp] cat >foo
foo
bar
baz
[~/tmp] irb
irb(main):001:0> f = File.open("foo", "r+")
=> #<File:foo>
irb(main):002:0> f.puts "FOO"
=> nil
irb(main):003:0> f.seek 8
=> 0
irb(main):004:0> f.puts "BAZ"
=> nil
irb(main):005:0> f.rewind
=> 0
irb(main):006:0> f.read
=> "FOO\nbar\nBAZ\n"
irb(main):007:0> f.close
=> nil
irb(main):008:0> [~/tmp] cat foo
FOO
bar
BAZ

--
vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

Robert Dober

6/11/2007 8:06:00 PM

0

On 6/11/07, Li Chen <chen_li3@yahoo.com> wrote:
> Hi all,
>
> I just wonder what is the Ruby way to update a file in place. Do I need
> to open a temporary/new file for writing and then rename the temporary
> file?
>
> Thanks,
>
> Li
>
> --
> Posted via http://www.ruby-....
>
No not necessarily, that depends how you can access the file, you can
use Ruby as an inplace filter on a file

ruby -i.bup -ne 'puts $_.gsub(/foo/,"bar")' somefile

will edit somefile and create a backup copy somefile.bup of the
original. Now when it comes to using files inside an application
things are little bit more complicated :(

HTH
Robert
>


--
You see things; and you say Why?
But I dream things that never were; and I say Why not?
-- George Bernard Shaw

Luis Parravicini

6/11/2007 8:08:00 PM

0

On 6/11/07, Li Chen <chen_li3@yahoo.com> wrote:
> I just wonder what is the Ruby way to update a file in place. Do I need
> to open a temporary/new file for writing and then rename the temporary
> file?

There is also the '-i' argument to ruby. The example is from the man page:
================================
% echo matz > /tmp/junk
% cat /tmp/junk
matz
% ruby -p -i.bak -e "$_.upcase!" /tmp/junk
% cat /tmp/junk
MATZ
% cat /tmp/junk.bak
matz
================================

--
Luis Parravicini
http://ktulu.co...

Li Chen

6/11/2007 8:55:00 PM

0

Where can I find some information about mmap?

thanks,

Li



--
Posted via http://www.ruby-....

Bill Guindon

6/11/2007 9:12:00 PM

0

On 6/11/07, Li Chen <chen_li3@yahoo.com> wrote:
> Where can I find some information about mmap?

Google is your friend...
http://www.google.com/search?source=ig&hl=en&q=ruby+mmap&btnG=Goo...

http://raa.ruby-lang.org/pro...

> thanks,
>
> Li
>
>
>
> --
> Posted via http://www.ruby-....
>
>


--
Bill Guindon (aka aGorilla)
The best answer to most questions is "it depends".

barjunk

6/11/2007 10:20:00 PM

0

On Jun 11, 1:11 pm, "Bill Guindon" <agori...@gmail.com> wrote:
> On 6/11/07, Li Chen <chen_...@yahoo.com> wrote:
>
> > Where can I find some information about mmap?
>
> Google is your friend...http://www.google.com/search?source=ig&hl=en&q=ruby+mmap&bt......
>
> http://raa.ruby-lang.org/pro...
>
> > thanks,
>
> > Li
>
> > --
> > Posted viahttp://www.ruby-....
>
> --
> Bill Guindon (aka aGorilla)
> The best answer to most questions is "it depends".

Although it may be wrong, I recently used lockfile and temporary files
to do inline editing. It is probably inefficient, but it seems to
work for what I am using it for.

Maybe someone can point out how to use the -i feature of ruby from
within the program instead of a shell command, that would work nice
as well.

In the application I was working on, there were possibilities for
multiple access at the same time.

Mike B.

lrlebron@gmail.com

6/12/2007 2:23:00 AM

0

On Jun 11, 2:42 pm, Li Chen <chen_...@yahoo.com> wrote:
> Hi all,
>
> I just wonder what is the Ruby way to update a file in place. Do I need
> to open a temporary/new file for writing and then rename the temporary
> file?
>
> Thanks,
>
> Li
>
> --
> Posted viahttp://www.ruby-....

I've used the rio library for this before. http://rio.ruby....
The website has some very good examples on how to use it.

Luis

barjunk

6/12/2007 6:10:00 AM

0

On Jun 11, 6:23 pm, "lrleb...@gmail.com" <lrleb...@gmail.com> wrote:
> On Jun 11, 2:42 pm, Li Chen <chen_...@yahoo.com> wrote:
>
> > Hi all,
>
> > I just wonder what is the Ruby way to update a file in place. Do I need
> > to open a temporary/new file for writing and then rename the temporary
> > file?
>
> > Thanks,
>
> > Li
>
> > --
> > Posted viahttp://www.ruby-....
>
> I've used the rio library for this before.http://rio.ruby....
> The website has some very good examples on how to use it.
>
> Luis

That's a nice library...I didn't notice any thing about locking the
file object. I'm assuming that that would be done outside the use of
the rio object.

I was also wondering if you thought you could use that library to read
files that have records that look like:

start line 1
line 2
line 3
end line4

and treat the above four lines as a record?

Mike B.

lrlebron@gmail.com

6/12/2007 5:03:00 PM

0

On Jun 12, 1:10 am, barjunk <barj...@attglobal.net> wrote:
> On Jun 11, 6:23 pm, "lrleb...@gmail.com" <lrleb...@gmail.com> wrote:
>
>
>
> > On Jun 11, 2:42 pm, Li Chen <chen_...@yahoo.com> wrote:
>
> > > Hi all,
>
> > > I just wonder what is the Ruby way to update a file in place. Do I need
> > > to open a temporary/new file for writing and then rename the temporary
> > > file?
>
> > > Thanks,
>
> > > Li
>
> > > --
> > > Posted viahttp://www.ruby-....
>
> > I've used the rio library for this before.http://rio.ruby....
> > The website has some very good examples on how to use it.
>
> > Luis
>
> That's a nice library...I didn't notice any thing about locking the
> file object. I'm assuming that that would be done outside the use of
> the rio object.
>
> I was also wondering if you thought you could use that library to read
> files that have records that look like:
>
> start line 1
> line 2
> line 3
> end line4
>
> and treat the above four lines as a record?
>
> Mike B.

I used it to clean up some code that was converted from vb6 to vb.net
The converter left a bunch of comments in the code that started with
"UPGRADE". I also went ahead and change the old "On Error Go To
Handler", "ErrHandler", and "Resume Next" strings to vb.net's "Try",
"Catch ex as Exception" and "End Try" strings

This is what the code looks like

require 'rio'
rio('C://test').all.files('*.vb') do |f|
rio(f) <f.contents.gsub(/'UPGRADE.*\s/,"").gsub(/On Error GoTo
ErrHandler/,"Try").gsub(/ErrHandler:/,"Catch ex as Exception\n").gsub(/
Resume Next/,"End Try")
end

The second line tells rio to look at all the files ending in .vb in
the C://test folder
The third line does a string substitution in the currently open file

BTW, it was very fast.


Luis