realpath for luafilesystem

[tst2005]

Hello luafilesystem should have a realpath like luaposix. It is very difficult to implement in lua with the existing lfs API. Some times, I only require luaposix only for this feature...

Regards,

[robertlzj]

Hi, in higher version, I think lfs.symlinkattributes(filepath).target is the real path? - subject path if filepath is symbolic path.

[tst2005]

@robertlzj no, the target value is the (absolute or relative path) of the symlink.

You can have a foo1 symlink pointing to bar or a foo2 symlink pointing to /home/xyz/bar

in /home/xyz/
foo1 -> bar
foo2 -> /home/xyz/bar

The realpath is use to travel in all "directories" and get out of any symlink to get a real uniq storage path. It is usefull in more complicated case like

d /storage/
d /storage/users/
d /storage/users/xyz
l /home -> /storage/users

• in this case the realpath of /home/xyz is /storage/users/xyz
• in this case the realpath of /home/xyz/foo1 is /storage/users/xyz/bar and not /home/xyz/bar
• in this case the realpath of /home/xyz/foo2 is /storage/users/xyz/bar and not /home/xyz/bar

If we want to implement the realpath job in lua, we need to

• get the full path (the target value if it is absolute, or the current path + the target value), /home/xyz/bar in the current sample
• start at the first left directory, if it is a link, substitute the value of the first directory by the symlink target value BUT before we also need to get the real path of this value.
• do the same thing with the next item in the path

It is a little complex ... the system realpath know how to do this job perfectly !

Regards,

[robertlzj]

Hi, thinks for your introduce about about realpath - the final path without symbolic. I think it's easy? to iterate each directory and expand if it is symlink then recurs iterate, at last make up the realpath. If there is realpath in system would be nice of cause.

And in windows, I had just compare lfs.link/lfs.symlinkattributes.target and ln.exe. target also make sense on hardlink, if it is in virtual volume (which is treated as symlink/junction directory?), it points to actual directory of virtual volume.

Other test on multi levels of symlink, substitute virtual volume, and multi symlink parts in path. I had thought final source above is realptah.

local lfs=require'lfs'
local vb=[[G:\]]--virtual base (on virtual volume)
local ab=[[E:\VirtualVolume\]]--actual base
if not lfs.attributes(vb) then
    assert(lfs.attributes(ab))
    os.execute('subst '..vb..' '..ab)
end
lfs.chdir(vb)
assert(not lfs.attributes'D' and not lfs.attributes'S')
os.execute('mkdir D')--origin
assert(lfs.link('D','S',true))--symlink directory
--
lfs.chdir(vb..[[S\]])
local E={close=function()end}
assert(not (io.open'O.txt' or E):close() and not (io.open'S.txt' or E):close() and not (io.open'S2.txt' or E):close() and not (io.open'S2b.txt' or E):close() and not (io.open'H.txt' or E):close() and not (io.open'Hb.txt' or E):close() and not (io.open'H2.txt' or E):close() and not (io.open'H2b.txt' or E):close())
----O: origin, H: config as hardlink, S: symlink
io.open('O.txt','w'):close()
lfs.link('O.txt','S.txt',true)
--hardlink
lfs.link('S.txt','H.txt')
os.execute('ln >nul 2>nul S.txt Hb.txt')
--symlink level 2
lfs.link('S.txt','S2.txt',true)
os.execute('ln >nul 2>nul --symbolic S.txt S2b.txt')
--hardlink level 2
lfs.link('S2.txt','H2.txt')
os.execute('ln >nul 2>nul S2.txt H2b.txt')
----
assert(lfs.symlinkattributes'H.txt'.mode=='link')
assert(lfs.symlinkattributes'Hb.txt'.mode=='link')
assert(lfs.symlinkattributes'S.txt'.mode=='link')
assert(lfs.symlinkattributes'S2.txt'.mode=='link')
assert(lfs.symlinkattributes'S2b.txt'.mode=='link')
assert(lfs.symlinkattributes'H2.txt'.mode=='link')
assert(lfs.symlinkattributes'H2b.txt'.mode=='link')
----
local function ln_target(fn)--show the target of a symbolic link
    local r=io.popen('ln --symbolic '..fn)
    return string.match(r:read'a','%-> (.+)\n')
end
assert(ln_target'H.txt'=='O.txt')
assert(ln_target'Hb.txt'=='O.txt')
assert(ln_target'S.txt'=='O.txt')
assert(ln_target'S2.txt'=='S.txt')
assert(ln_target'S2b.txt'=='S.txt')
assert(ln_target'H2.txt'=='S.txt')
assert(ln_target'H2b.txt'=='S.txt')
----
local t=(lfs.attributes(ab) and ab or vb)..[[D\O.txt]]
assert(lfs.symlinkattributes'H.txt'.target==t)
assert(lfs.symlinkattributes'Hb.txt'.target==t)
assert(lfs.symlinkattributes'S.txt'.target==t)
assert(lfs.symlinkattributes'S2.txt'.target==t)
assert(lfs.symlinkattributes'S2b.txt'.target==t)
assert(lfs.symlinkattributes'H2.txt'.target==t)
assert(lfs.symlinkattributes'H2b.txt'.target==t)
----
os.execute('del O.txt S.txt S2.txt S2b.txt H.txt Hb.txt H2.txt H2b.txt')
lfs.chdir(vb)
--
os.execute('rmdir D')
os.execute('rmdir S')
print'test done.'