[fedora] dd

[xinyou yan]

2011/9/4 suvayu ali <fatkasuvayu+linux at gmail.com>:
> Hi Xinyou,
>
> On Sun, Sep 4, 2011 at 4:53 PM, xinyou yan <yxy.716 at gmail.com> wrote:
>>> I am not sure what the problem is.
>>> The following works for me:
>>> tar cf archive.tar first
>>> tar -rf archive.tar second
>> Yes it can , But tar czf tar rzf can't work
>> Second :
>>
>> if I use
>> gzip -c file1 >>  yyy.test
>> How can I unpress yyy.test to file1 as file1
>> I test like it
>> gzip -c test1 > 1.test
>> We can use
>>
>> gunzip -c 1.test >test1
>>
>> to achieve my answer .
>> However :
>> gzip -c test1 >> 1.test
>> gzip -c test2 >> 1.test
>>
>> I just gunzip -c 1.test > test1 (the size of test1 now is  the sum
>> test1 and test2 before)
>>
>> How can i use gunzip  to separate the  two file ?
>> I wonder  >>  can remember there are two file ?
>
> I think you are mixing up compression and archiving as similar things.
> They should be done in a particular order:
>
> 1. to create: archive -> compress
> 2. to modify: decompress -> modify archive -> compress
> 3. restore:   decompress -> unarchive
>
> Now (1) and (3) can be done in one step using the -z or -j option to
> tar, however for (2) you need to decompress first using `gunzip' or `gzip
> -d' before you can use `tar -r -f <archivefile.tar>' to modify it.
>
> To give you an example:
>
> $ tar -czf backup.tar.gz *.org # backup all .org files
> $ tar -tzf backup.tar.gz # test if it worked
> analysis.org
> coding.org
> fiddle.org
> languages.org
> meetings.org
> notes.org
> org-help.org
> $ gunzip backup.tar.gz # decompress the compressed archive
> $ tar -rf backup.tar *.org_archive # add .org_archive files
> $ gzip backup.tar # compress modified archive
> $ tar -tzf backup.tar.gz # test again
> analysis.org
> coding.org
> fiddle.org
> languages.org
> meetings.org
> notes.org
> org-help.org
> analysis.org_archive
> meetings.org_archive
> notes.org_archive
> $ tar -xzf backup.tar.gz '*.org' # restore only .org files
> $ ls
> analysis.org  backup.tar.gz  coding.org  fiddle.org  languages.org
> meetings.org  notes.org  org-help.org
>
> In the future I would recommend try going through the manual page for
> tar and gzip carefully (`man tar' and `man gzip').
>
> I hope this helps.

Yes it is very clear , you suggestion is good .
By the way , I said before gzip  with >>  can  be achieved ?
gzip  -c  make the file be compressed to standout , then redirect ,
Can we decompress it with some method ?


>
> --
> Suvayu
>
> Open source is the future. It sets us free.
> --
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