Moving files with ruby

Hello all,

A script I have written needs the ability to move files. I thought I would be
clever and use File.rename(old, newdir + new) but this is giving me an error:
`rename': Invalid cross-device link. I gather this is because I am renaming
the file to a different partition.

So then I found FileUtils and used:
require 'fileutils'
include FileUtils
mv( old, new)

This is working but seems an overly verbose and convoluted way to move a file.
I had a look at the fileutils.rb source and found this (for 'mv'):
# Moves file(s) +src+ to +dest+. If +file+ and +dest+ exist on the different
# disk partition, the file is copied instead

So I guess my real question is: is there a technical reason or some arbitrary
reason there is no File.move() method that can handle this transparently? I
would think it would be quite useful...

Any insight is appreciated,
-d

···

--
darren kirby :: Part of the problem since 1976 :: http://badcomputer.org
"...the number of UNIX installations has grown to 10, with more expected..."
- Dennis Ritchie and Ken Thompson, June 1972

darren kirby wrote:

Hello all,

A script I have written needs the ability to move files. I thought I would
be clever and use File.rename(old, newdir + new) but this is giving me an
error: `rename': Invalid cross-device link. I gather this is because I am
renaming the file to a different partition.

No, it is because you are trying to use "rename" to physically move a file,
and the system is objecting to this misconception. File.rename can only
rename files, it cannot move them. It works only on one storage
device/volume/whatever.

So then I found FileUtils and used:
require 'fileutils'
include FileUtils
mv( old, new)

This is working but seems an overly verbose and convoluted way to move a
file.

Umm, compared to what? It moves the file using a method named "mv", just
like the Linux/Unix command of the same name.

I had a look at the fileutils.rb source and found this (for 'mv'):
# Moves file(s) +src+ to +dest+. If +file+ and +dest+ exist on the
# different disk partition, the file is copied instead

That is what "mv" does. If the new and old filenames and paths allow the
file to remain on the same device, a simple rename is carried out. If not,
the file is copied to the destination and deleted from the source.

So I guess my real question is: is there a technical reason or some
arbitrary reason there is no File.move() method that can handle this
transparently? I would think it would be quite useful...

It might be because not all operating systems on which Ruby can be installed
know the "mv" operation as described above. Just a guess.

···

--
Paul Lutus
http://www.arachnoid.com

quoth the Paul Lutus:

darren kirby wrote:
> Hello all,
>
> A script I have written needs the ability to move files. I thought I
> would be clever and use File.rename(old, newdir + new) but this is giving
> me an error: `rename': Invalid cross-device link. I gather this is
> because I am renaming the file to a different partition.

No, it is because you are trying to use "rename" to physically move a file,
and the system is objecting to this misconception. File.rename can only
rename files, it cannot move them. It works only on one storage
device/volume/whatever.

Well, I think that's pretty much what I said. If you 'rename' a file
from /somepath/somefile.txt to /someotherpath/somefile.txt within the same
partition you have effectively 'moved' it haven't you...

> So then I found FileUtils and used:
> require 'fileutils'
> include FileUtils
> mv( old, new)
>
> This is working but seems an overly verbose and convoluted way to move a
> file.

Umm, compared to what? It moves the file using a method named "mv", just
like the Linux/Unix command of the same name.

I am typically very impressed with how much you can do with a little amount of
code in Ruby. For instance, I only had to add one line to add some recursive
directory handling in my script:

From:
files += Dir.glob("*.#{t}")
To:
files += Dir.glob("**/*.#{t}")

Whereas to move a file, a fairly basic operation, I need four lines of code:

require 'fileutils'
include FileUtils
cp(old, new )
rm (old)

I have to change "mv" to "cp" and add the "rm" because the old file is not
automatically removed...

> I had a look at the fileutils.rb source and found this (for 'mv'):
> # Moves file(s) +src+ to +dest+. If +file+ and +dest+ exist on the
> # different disk partition, the file is copied instead

That is what "mv" does. If the new and old filenames and paths allow the
file to remain on the same device, a simple rename is carried out. If not,
the file is copied to the destination and deleted from the source.

Right, I've got that...

> So I guess my real question is: is there a technical reason or some
> arbitrary reason there is no File.move() method that can handle this
> transparently? I would think it would be quite useful...

It might be because not all operating systems on which Ruby can be
installed know the "mv" operation as described above. Just a guess.

I am just wondering because there are (AFAIK) other methods that handle the
operation transparently even though the underlying OS does it differently.

Not trying to troll, I am just curious...

-d

···

--
darren kirby :: Part of the problem since 1976 :: http://badcomputer.org
"...the number of UNIX installations has grown to 10, with more expected..."
- Dennis Ritchie and Ken Thompson, June 1972

well
system("mv #{file}")
is also possible ,)

include FileUtils isnt needed so that should reduce your
LOC by -1

Doesnt FileUtils have
mv(src, dest, options)
?

Anyway, why not this?

http://www.ruby-doc.org/core/classes/FileUtils.html#M002613

···

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

Marc Heiler wrote:

well
system("mv #{file}")
is also possible ,)

But not generic for cross-platform re-use.

quoth the Marc Heiler:

well
system("mv #{file}")
is also possible ,)

I may be wrong, but I always had the impression that using a system command to
do something available within the language is considered a kludge.

include FileUtils isnt needed so that should reduce your
LOC by -1

When I comment the line out I get:
undefined method `cp' for main:Object (NoMethodError)

Doesnt FileUtils have
mv(src, dest, options)
?

Yes, it does. But the thing is that if you are moving the file across
partitions it will only copy and not delete the original file. I will not
know if we are moving cross-partition, so I have to use cp and rm...

Anyway, why not this?

http://www.ruby-doc.org/core/classes/FileUtils.html#M002613

From the link: "If file and dest exist on the different disk partition, the
file is copied instead."

-d

···

--
darren kirby :: Part of the problem since 1976 :: http://badcomputer.org
"...the number of UNIX installations has grown to 10, with more expected..."
- Dennis Ritchie and Ken Thompson, June 1972