[Bug-tar] Symlink dereference behaviour

[Vladimir A . Pavlov]

Hi!

 In tar info page the following is written:

 "
 When reading from an archive, the `--dereference' (`-h') option
 causes `tar' to follow an already-existing symbolic link when `tar'
 writes or reads a file named in the archive.
 "

 I wrote a simple script and it seems that symlinks to files are not
 followed (whereas symlinks to directories are followed).

 In other words, if I extract a file using -h and a symlink with the same
 name exists then the symlinks is just removed and a new file is created.
 But if I extract a directory using -h and a symlink with the same name
 exists, the symlinks is followed. So, the behaviour is different for files
 and directories.

 I'm writing some script and I wouldn't like the following versions of tar to
 break it, so I have questions:
 1. Is this behaviour a bug, or does it works as expected?
 2. Is there a possibility this behaviour will be changed in future?

 The following output demonstrates the issue.

 In the output, the header "file (-h)" (and similar) means we're checking
 how a _file_ overwrites a symlink to a _file_ if being extracted
 with _-h_ option. Two groups of lines for each header are filesystem
 status before and after extracting so we can see the change.

 Tar 1.26 is used.

 /tmp$ ./tar.sh

 file ()

 drwxr-xr-x 3 pkg users 4096 Nov 1 14:54 dst
 drwxr-xr-x 2 pkg users 4096 Nov 1 14:54 dst/dir
 -rw-r--r-- 1 pkg users 0 Nov 1 14:54 dst/dir/regfile
 lrwxrwxrwx 1 pkg users 7 Nov 1 14:54 dst/dir/symfile -> regfile

 drwxr-xr-x 3 pkg users 4096 Nov 1 14:54 dst
 drwxr-xr-x 2 pkg users 4096 Nov 1 14:54 dst/dir
 -rw-r--r-- 1 pkg users 0 Nov 1 14:54 dst/dir/regfile
 -rw-r--r-- 1 pkg users 5 Nov 1 14:54 dst/dir/symfile

 dir ()

 drwxr-xr-x 2 pkg users 4096 Nov 1 14:54 dst
 lrwxrwxrwx 1 pkg users 1 Nov 1 14:54 dst/dir -> .
 -rw-r--r-- 1 pkg users 0 Nov 1 14:54 dst/symfile

 drwxr-xr-x 3 pkg users 4096 Nov 1 14:54 dst
 drwxr-xr-x 2 pkg users 4096 Nov 1 14:54 dst/dir
 -rw-r--r-- 1 pkg users 5 Nov 1 14:54 dst/dir/symfile
 -rw-r--r-- 1 pkg users 0 Nov 1 14:54 dst/symfile

 file (-h)

 drwxr-xr-x 3 pkg users 4096 Nov 1 14:54 dst
 drwxr-xr-x 2 pkg users 4096 Nov 1 14:54 dst/dir
 -rw-r--r-- 1 pkg users 0 Nov 1 14:54 dst/dir/regfile
 lrwxrwxrwx 1 pkg users 7 Nov 1 14:54 dst/dir/symfile -> regfile

 drwxr-xr-x 3 pkg users 4096 Nov 1 14:54 dst
 drwxr-xr-x 2 pkg users 4096 Nov 1 14:54 dst/dir
 -rw-r--r-- 1 pkg users 0 Nov 1 14:54 dst/dir/regfile
 -rw-r--r-- 1 pkg users 5 Nov 1 14:54 dst/dir/symfile

 dir (-h)

 drwxr-xr-x 2 pkg users 4096 Nov 1 14:54 dst
 lrwxrwxrwx 1 pkg users 1 Nov 1 14:54 dst/dir -> .
 -rw-r--r-- 1 pkg users 0 Nov 1 14:54 dst/symfile

 drwxr-xr-x 2 pkg users 4096 Nov 1 14:54 dst
 lrwxrwxrwx 1 pkg users 1 Nov 1 14:54 dst/dir -> .
 -rw-r--r-- 1 pkg users 5 Nov 1 14:54 dst/symfile

 The script in question follows:

 /tmp$ cat tar.sh 
 #!/bin/sh

 for opt in '' '-h'; do

 echo
 echo "file ($opt)"
 echo

 rm -rf src dst

 mkdir -p src/dir
 echo file >src/dir/symfile

 mkdir -p dst/dir
 touch dst/dir/regfile
 ln -s regfile dst/dir/symfile

 find dst |xargs ls -ld
 ( cd src; tar -cf - . ) |tar -x $opt -f - -C dst
 echo
 find dst |xargs ls -ld

 echo
 echo "dir ($opt)"
 echo

 rm -rf src dst

 mkdir -p src/dir
 echo file >src/dir/symfile

 mkdir -p dst
 touch dst/symfile
 ln -s . dst/dir

 find dst |xargs ls -ld
 ( cd src; tar -cf - . ) |tar -x $opt -f - -C dst
 echo
 find dst |xargs ls -ld

 done

 --
 pv4