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Day 16

Notes

  • Creating an archive from some songs starting with S, tar -cvf songs.tar S*

  • Checking the archive and individual file sizes.

  • tar -tf songs.tar | awk '{printf "'\''%s'\''\n", $0}' | xargs ls -l | awk '{print $5}' | awk '{sum+=$1;} END {printf "%0.3f KB", sum/1024}'

or shorter

  • tar -tvf songs.tar | awk '{print $3}' | awk '{sum+=$1;} END {printf "%0.3f KB", sum/1024}'

they both give -

35474.563 KB

ls -l songs.tar | awk '{printf "%0.3f KB", $5/1024}' gives -

35480.000 KB

  • Creating compressed archive tar -cvzf songsc.tar.gz S* using gzip and bzip2 compression methods. tar -cvjf songsc.tar.gz S*.

  • A compressed tar archive like this is known as a "tarball".

  • Comparing sizes

  • ls -l songsc.tar.gz | awk '{printf "%0.3f KB" ,$5/1024}' gives -
    35211.450 KB

  • ls -l songs.tbz2 | awk '{printf "%0.3f KB", $5/1024}' gives - 35288.767 KB

filename size
S* 35474.563 KB
songs.tar 35480.000 KB
songsc.tar.gz 35211.450 KB
songs.tbz2 35288.767 KB

S* refers to all the files in the archive

  • gzip (-z), xz (-J), bzip2 (-j) are some of the compresssion algorithms supported by tar.

  • tar can detect the compression used and use the corresponding decompression method to get back the files. So, tar -xf archivename will work for tar.bz2 (aka tbz2), tar.gz (aka tgz), etc.

  • Extracting only the files "Samarkand Overture - Yuri on Ice.mp3 and Spyair - Imagination.mp3"

  • A listing tar -tf songs.tbz2 of the tar shows us that it has the following files -

Samarkand Overture - Yuri on Ice.mp3
Shounanno Kaze - Grand Blue.mp3
SixTONES - NAVIGATOR full.mp3
South_Side_Symphony,_ViolinGamer_Nightfall_From__Naruto_Shippuden_.mp3
Spyair - Imagination.mp3
Survive Said The Prophet - Found & Lost.mp3

the output was pasted using Ctrl v after running tar -tf songs.tbz2 | xclip -selection clipboard

  • We use tar -C newdir/ -xvf songs.tbz2 --wildcards Spy* Samar* to extract the two needed files to newdir (it should exist). -C option is order sensitive, it tells tar to change into the following dir and then perform an action. So adding -C to the end of command won't extract the files in the dir. (Always see the man pages.)

Readings

  • What is a .bz2 file - and how would you extract the files from it?
  • Research how absolute and relative paths are handled in tar - and why you need to be careful extracting from archives when logged in as root
  • You might notice that some tutorials write "tar cvf" rather than "tar -cvf" with the switch character - do you know why? (Traditional way for options vs UNIX way vs GNU way)
  • 18 Tar Command Examples in Linux
  • Linux TAR Command
  • Linux tar command tutorial (video)