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IgorAlves
Asked: 2018-03-09 05:39:31 +0800 CST

How do I programatically get the file or directory name after extracting after a tar archive?

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I have a process in my Dockerfile with the follow steps:

  1. Download the tar file using wget.
  2. untar the file.
  3. Perform some operation with the file . In this case, move content to another place.

The follow code works until ffmpeg version still 3.4.1. So, today the available version for ffmpeg is 3.4.2 and the code is not working.

I want to find a way to grab back the filename after the untar process and pass it to the next steps

RUN wget http://johnvansickle.com/ffmpeg/releases/ffmpeg-release-64bit-static.tar.xz
RUN tar xf ffmpeg-release-64bit-static.tar.xz
RUN mv ffmpeg-3.4.1-64bit-static/ffmpeg /usr/local/bin/
RUN mv ffmpeg-3.4.1-64bit-static/ffprobe /usr/local/bin/

It could be something like this:

RUN DIRNAME = tar xf ffmpeg-release-64bit-static.tar.xz
RUN mv $DIRNAME/ffmpeg /usr/local/bin/
RUN mv $DIRNAME/ffprobe /usr/local/bin/

How could I achieve this?

command-line tar

3 Answers

  1. Don't. Instead, get tar to put the contents in a directory of your choosing.

    1. tar can remove n components of the path of each file (--strip-components)
    2. tar can apply arbitrary sed expressions to change the path of each file (--transform)

    So I'd do something like:

    mkdir ffmpeg
wget -O - http://johnvansickle.com/ffmpeg/releases/ffmpeg-release-64bit-static.tar.xz |
  tar --xz -x -C ffmpeg --strip-components=1

    Here, I made the directory myself, and told tar to extract there (the -C option), while removing the first component from the path of the extracted files. So ffmpeg-3.4.1-64bit-static/ffprobe becomes ffprobe inside the directory ffmpeg.

    Or:

    wget -O - http://johnvansickle.com/ffmpeg/releases/ffmpeg-release-64bit-static.tar.xz |
  tar --xz -x --transform='s:[^/]*/:ffmpeg/'

    Here, I simply changed the first component of the path to ffmpeg, so I didn't need to make the directory myself. So, ffmpeg-3.4.1-64bit-static/ffmpeg becomes ffmpeg/ffmpeg.

    Or, knowing that you specifically want to dump those particular files in /usr/local/bin, use -C to directly place the files there, while removing all directory components and selecting exactly those files you want to extract:

    wget -O - http://johnvansickle.com/ffmpeg/releases/ffmpeg-release-64bit-static.tar.xz |
  tar Jx -C /usr/local/bin --transform='s:.*/::' --wildcards '*/ffmpeg' '*/ffprobe'

    With any tar, you can specify the files to be extracted. With GNU tar, you can also use wildcards.

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  2. The command to get the directory name from the tar.xz file is:

    tar tJvf tar-file-name.tar.xz | head -1 | awk '{print $6}'

    You'll need to:

    1. Get the directory name (e.g. using above solution) and save it in a variable
    2. decompress the tar.xz file (e.g. using tar xf command)
    3. move the files using the directory variable

    Explanation how to get the directory name from a tar file:

    Tar parameters:

    -f file
-J xz compression
-t list content
-v verbose

    head -1 - prints the file line

    awk '{print $6}' - print the 6th elements which is the directory name

    Examples:

    1. tar.xz example:

      tar tJvf coreutils-8.22.tar.xz | head -1 | awk '{print $6}'

    Results with:

    coreutils-8.22/

    1. tar.bz2 example for ffmpeg-3.4.2.tar.bz2

      tar tjvf ffmpeg-3.4.2.tar.bz2 | head -1 | awk '{print $6}'

    Results with:

    ffmpeg-3.4.2/

    Note that for bz2 compressed files I used the tar j flag

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  3. Like that:

    $ tar tf ffmpeg-release-64bit-static.tar.xz | head -1 | cut -d '/' -f1
ffmpeg-3.4.2-64bit-static

    Notice that GNU tar does not require -j, -z etc., it can detect archive type automatically.

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