Moving files with ruby

Ruby
1

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

2

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.

3

quoth the Paul L.:

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

4

Marc H. wrote:

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

But not generic for cross-platform re-use.

5

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

6

quoth the Marc H.:

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