Re: Patch for "mv -s" option

[Brendan Byrd/SineSwiper]

Philip Rowlands wrote:
> On Fri, 5 Nov 2004, Brendan Byrd/SineSwiper wrote:
>
> > Also, I have a question about how files are moved.  Currently, all files
> > are copied to a new diskspace, and then the old diskspace is removed.
>
> Only when the file is moving across filesystem boundaries.
>
> Try this to see how mv usually behaves:
> $ strace -e trace=file mv /tmp/foo /tmp/bar

execve("/bin/mv", ["mv", "a", "/b"], [/* 54 vars */]) = 0
open("/etc/ld.so.preload", O_RDONLY)    = -1 ENOENT (No such file or 
directory)
open("/etc/ld.so.cache", O_RDONLY)      = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=32570, ...}) = 0
open("/lib/libc.so.6", O_RDONLY)        = 3
fstat64(3, {st_mode=S_IFREG|0755, st_size=1475331, ...}) = 0
open("/usr/lib/locale/locale-archive", O_RDONLY|O_LARGEFILE) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=32058672, ...}) = 0
stat64("/b", 0xbffff4c0)                = -1 ENOENT (No such file or 
directory)
lstat64("a", {st_mode=S_IFREG|0644, st_size=454656, ...}) = 0
lstat64("/b", 0xbffff280)               = -1 ENOENT (No such file or 
directory)
rename("a", "/b")                       = 0

Okay, after looking at the code again, this makes more sense.  The copy 
routine doubles as a rename command if in move_mode, hence the 
"rename_successful" variable.

Paul Eggert wrote:
> Brendan Byrd/SineSwiper <address@hidden> writes:
>
>>I hashed out a patch for mv which is more or less the opposite of the
>>"--symbolic-link" option for cp.  Instead of creating symlinks on the
>>destination before the copy, it creates symlinks on the source after
>>the move.
>
> Before we talk about the patch itself (which was not enclosed in your
> email, by the way), could you give an illustration why such an option
> is useful?  Often the most important part of such changes is the
> documentation, and the illustration should be put there.

Hmmm...it was in an attachment, according to my Sent file.  I guess the 
mailing list doesn't support attachments.  I could sent it in the 
e-mail, but I'm afraid that long lines would get word wrapped.  Is there 
a place to send attachments/patches?

Sorry, I did forget about the man page, but I can easily add that in. 
(The mv --help was changed, though.)  I just wanted to release the patch 
to see if the idea would be applied.  As far as application and 
usefulness, three things come to mind:

1. Retaining glob information during a mv/ln.  This was my itch to 
stratch.  I wanted to move IRC *.log files to /var/log/ircd and then 
link those to the moved files.  Unforunately, after you move them, you 
can't just type "ln /var/log/ircd/*.log ." if there are log files 
already in the directory other than the ones you move.  With the mv -s, 
all of the glob information is retained, so it knows exactly which files 
get the symlinks.

2. Moving directories from one filesystem to another.  A common way of 
shifting HD space on a multi-partitioned system is to move a large 
directory from the full partition, to area owned by partition with space 
to spare, followed by symlinking to the directory.  This is made easier 
with a "mv -s" command.

3. Better compatibility/completeness with the cp command.  In comparison 
to the cp command, the mv command is bereft of options.  It's probably 
true that the cp command has a bunch of little used or legacy options, 
but this was one that I thought would have been added to mv already.

--
Brendan Byrd/SineSwiper <address@hidden>
Computer techie, Perl hacker, and all-purpose Internet guru
Resonator Software (http://www.ResonatorSoft.org/)