Why do TAR files always need to be decompressed twice?
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I've noticed that whenever I download a TAR file (and it usually is TAR.GZ) and decompress it, there always is yet another compressed file that needs to be decompressed. Why don't folks just do a single compression?
Because a TAR file isn't a compressed file. A GZIP file is. So them UNIX folk put files in a TAR then GZIP it. Deal with it.
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I've noticed that whenever I download a TAR file (and it usually is TAR.GZ) and decompress it, there always is yet another compressed file that needs to be decompressed. Why don't folks just do a single compression?
double de-compression? you're doing it wrong. the proper [as per design] procedure: 1. un-gzip it and redirect the output to the tape device, ... (may necessitate co-ordinated use of 2 hands if tape device doesn't have automatic start/stop control) 2. rewind the tape ... (on some sites a separate rewinding machine - submit both the tape and duly completed rewind request) 3. and then: un-tar (tar -x) it from the tape reader into the destination directory. ... (please remember: folders are where you keep your forms and notes, files are stored in directories.) some new-fangled versions of tar have gzip built right in, many operators cant grok that. kids these days: always looking for shortcuts.
This internet thing is amazing! Letting people use it: worst idea ever!
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double de-compression? you're doing it wrong. the proper [as per design] procedure: 1. un-gzip it and redirect the output to the tape device, ... (may necessitate co-ordinated use of 2 hands if tape device doesn't have automatic start/stop control) 2. rewind the tape ... (on some sites a separate rewinding machine - submit both the tape and duly completed rewind request) 3. and then: un-tar (tar -x) it from the tape reader into the destination directory. ... (please remember: folders are where you keep your forms and notes, files are stored in directories.) some new-fangled versions of tar have gzip built right in, many operators cant grok that. kids these days: always looking for shortcuts.
This internet thing is amazing! Letting people use it: worst idea ever!
Files are not stored in directories. (Nor in folders of course.)
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double de-compression? you're doing it wrong. the proper [as per design] procedure: 1. un-gzip it and redirect the output to the tape device, ... (may necessitate co-ordinated use of 2 hands if tape device doesn't have automatic start/stop control) 2. rewind the tape ... (on some sites a separate rewinding machine - submit both the tape and duly completed rewind request) 3. and then: un-tar (tar -x) it from the tape reader into the destination directory. ... (please remember: folders are where you keep your forms and notes, files are stored in directories.) some new-fangled versions of tar have gzip built right in, many operators cant grok that. kids these days: always looking for shortcuts.
This internet thing is amazing! Letting people use it: worst idea ever!
Tape? Tape? We don't use such new-fangled magnetics here! Send it to the card punch!
Sent from my Amstrad PC 1640 Bad command or file name. Bad, bad command! Sit! Stay! Staaaay... AntiTwitter: @DalekDave is now a follower!
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I've noticed that whenever I download a TAR file (and it usually is TAR.GZ) and decompress it, there always is yet another compressed file that needs to be decompressed. Why don't folks just do a single compression?
In plain English: A tar file is an (uncompressed) file(sssss) archive. i.e. a group of files together as one file. GZip compress 1 file. The tar archive. So you do in 2 steps is: 1. uncompress 2. unarchive Now, it's about your tools. Some too unpack both steps as one. Maybe use different tools if doing in 2 step is a bother?
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Files are not stored in directories. (Nor in folders of course.)
good point, the directory is just a list of name and inode number pairs. Such a simple system, could elegantly do things back then that NTFS still hasn't come close to without a whole mess of complicated hoops to jump through.
This internet thing is amazing! Letting people use it: worst idea ever!
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Tape? Tape? We don't use such new-fangled magnetics here! Send it to the card punch!
Sent from my Amstrad PC 1640 Bad command or file name. Bad, bad command! Sit! Stay! Staaaay... AntiTwitter: @DalekDave is now a follower!
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I've noticed that whenever I download a TAR file (and it usually is TAR.GZ) and decompress it, there always is yet another compressed file that needs to be decompressed. Why don't folks just do a single compression?
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megaadam wrote:
tar xvf fileMemories, oh Memories!!!
I'd rather be phishing!
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I've noticed that whenever I download a TAR file (and it usually is TAR.GZ) and decompress it, there always is yet another compressed file that needs to be decompressed. Why don't folks just do a single compression?
What program do you use to decompress? Winrar for instance decompresses in one step. 7zip on the other hand is not willing to make it simple for the user: [7-Zip / Discussion / Open Discussion:Treat .tar.gz extract as atomic operation?](https://sourceforge.net/p/sevenzip/discussion/45797/thread/5eb1b8d5/)
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I've noticed that whenever I download a TAR file (and it usually is TAR.GZ) and decompress it, there always is yet another compressed file that needs to be decompressed. Why don't folks just do a single compression?
Simples. Formats like ZIP employ compression on a file-by-file basis. This is obviously prone to poor rates of compression as compared to a scheme that can compress the entire contents of an archive, or in some cases, data that is contained within lots of small files. The solution is to slap all of the files together first in a monolithic chunk. You then run compression on that chunk in the (almost always delivered) hope that you'll achieve a smaller output than if the compressed output of all the contained files was then glued together into a single chunk. TAR - turn a bunch of files into one. GZ - compress a file.
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I've noticed that whenever I download a TAR file (and it usually is TAR.GZ) and decompress it, there always is yet another compressed file that needs to be decompressed. Why don't folks just do a single compression?
What are you downloading? Most source code bundles are just compressed with the .gz extension. Maybe if there were a bunch of videos, jpeg or pdf files, which have inbuilt compression, then the uncompressed .tar file might be as short, if not shorter than the tar.gz file. But muscle memory will automatically add the z option to tar to invoke gzip to compress the output. Similar, there's little point is adding the -C option to scp when transferring a .tar.gz file.
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I've noticed that whenever I download a TAR file (and it usually is TAR.GZ) and decompress it, there always is yet another compressed file that needs to be decompressed. Why don't folks just do a single compression?
.tgz and .tar.gz files are some file(s)/directory(ies) stored into a single tar (tape archive) file without compression, before being compressed using gzip. gzip (on its own) can only handle a single file. This is why it looks like it's compressed twice. I'm pretty sure if you specify the right arguments, you can decompress the .tgz with a single command.
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In plain English: A tar file is an (uncompressed) file(sssss) archive. i.e. a group of files together as one file. GZip compress 1 file. The tar archive. So you do in 2 steps is: 1. uncompress 2. unarchive Now, it's about your tools. Some too unpack both steps as one. Maybe use different tools if doing in 2 step is a bother?
A new .NET Serializer All in one Menu-Ribbon Bar Taking over the world since 1371!
Yes, what he said. You're probably used to ZIP files, which do both jobs in a single file format.
Paul Sanders http://www.alpinesoft.co.uk
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I've noticed that whenever I download a TAR file (and it usually is TAR.GZ) and decompress it, there always is yet another compressed file that needs to be decompressed. Why don't folks just do a single compression?
Because GZ refers to gzip - and TAR refers to Tape Archive - which is not compressed (though some Unixes do use "compress" to compress the files in the TAR archive as a default setting). You can decompress with -zxvf to do the decompress all in the one step. You probably also noticed that some have TGZ extensions, and some have TAR.GZ extensions - depending on the process used to create the archive. In short - the reason is the Unix tradition for small programs that do one thing well and allow you to pipe them into one another.
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I've noticed that whenever I download a TAR file (and it usually is TAR.GZ) and decompress it, there always is yet another compressed file that needs to be decompressed. Why don't folks just do a single compression?
A TAR file in your sense is indeed a TAR.GZ file, which embed two formats : TAR and GZ. Here's the process : 1. A TAR file is ceated, concatening several files together in their uncompressed form ; note that resulting TAR file is uncompressed, 2. A GZ file is created by compressing the previous TAR file. So to decompress a TAR.GZ file, you have to : 1. Decompress the compressed GZ file and 2. "Untar" (unarchive) the uncompressed resulting TAR file. Note that you can compress a TAR file with other popular compressors (bzip2 => TAR.BZ2, 7zip => TAR.7Z...).
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Simples. Formats like ZIP employ compression on a file-by-file basis. This is obviously prone to poor rates of compression as compared to a scheme that can compress the entire contents of an archive, or in some cases, data that is contained within lots of small files. The solution is to slap all of the files together first in a monolithic chunk. You then run compression on that chunk in the (almost always delivered) hope that you'll achieve a smaller output than if the compressed output of all the contained files was then glued together into a single chunk. TAR - turn a bunch of files into one. GZ - compress a file.
enhzflep wrote:
Formats like ZIP employ compression on a file-by-file basis. This is obviously prone to poor rates of compression as compared to a scheme that can compress the entire contents of an archive
If you experience significantly better compression by merging a lot of small files into one, either your average file size is extremely small (like in one classical Unix study showing that for the system as a whole, more than 80% of the files were less than 5 kbytes). Or, you misinterpret data: it is not poorer compression, but more metadata, administrative information. One large file requires one descriptor, five thousand tiny files require five thousand descriptors. That is not poorer rate of compression, but similar to gathering the five thousand files into one even without compression: That would save the space of 4999 inodes, as well as the internal fragmentation loss - if file sizes are evenly distributed: half an allocation unit (/disk block) per file. You save space by making this huge file, but it has nothing to do with data compression. If you want to make an exact comparison, you cannot compare the size of the .tar file to the size of the .tar.gz file. That sure would give you the compression rate of the .tar file, but to created the .tar file you had to add a noticable amount of metadata. So what you save by having only one file/compression descriptor, you partially loose to .tar administrative information. I keep a number of 'archives' of many small files in .zip format, saving space due to the compression, of course, but also a lot is saved by not wasting 2 Kbyte on each file in internal fragmentation. Another advantage of .zipping up these file groups: I frequently move the files between machines on USB sticks. Writing a few thousand files to a USB stick takes a lot of time to create the files. I guess that it has to do with USB stick writes not being cached, at least not to the same degree, and file creation requires lots of writes, even if the file contents is done in one single write. Writing a single .zip archive to a USB stick is several times faster than writing two thousand tiny files. A similar situation: We run a fairly large build system, with about a hundred build agents. A build may be producing dozens, in some cases hundreds, of individual artifacts. On the central server, distributing these artifacts, the inode table exploded when each artifact was treated separately. We were forced to modify the b
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double de-compression? you're doing it wrong. the proper [as per design] procedure: 1. un-gzip it and redirect the output to the tape device, ... (may necessitate co-ordinated use of 2 hands if tape device doesn't have automatic start/stop control) 2. rewind the tape ... (on some sites a separate rewinding machine - submit both the tape and duly completed rewind request) 3. and then: un-tar (tar -x) it from the tape reader into the destination directory. ... (please remember: folders are where you keep your forms and notes, files are stored in directories.) some new-fangled versions of tar have gzip built right in, many operators cant grok that. kids these days: always looking for shortcuts.
This internet thing is amazing! Letting people use it: worst idea ever!
