19.6 GNU tar Sampler

tar	GNU tar has plenty of features; some people would say "too many." I don't agree. GNU tar has features I wish I'd had for years in more "standard" versions. This article lists my favorites. For a complete list, check the documentation on the CD-ROM.

• Article 19.5 describes how to compress an archive file you've created. If you're using GNU tar , this is even easier, since tar itself can do the compression. Simply use the z option when writing or reading archives. For example, to make the gzip ped tar archive progs.tar.gz from all ".c" and ".h" files:

  % 
  
  tar cvzf progs.tar.gz *.c *.h
  
  

  Compressed tape archives aren't recommended because error recovery can be difficult.

• I've made the classic mistake of archiving files with their absolute pathnames ( 20.10 ) . GNU tar saves you from that goof. It always stores absolute pathnames as relative paths unless you add the --absolute-names option.

• Often I want to make a tape backup of my most recent work on a big project, but not all the thousands of files in a directory tree. The clumsy way to do that is by using find -mtime to make an include-file for the standard tar -I option. GNU tar to the rescue: its --after-date option lets me tell it what directories to look in and how recently the files should have been changed.

• When I extract an archive, I may be writing into a directory that has other files. The --keep-old-files option tells GNU tar not to overwrite existing files.

One caution about GNU tar : it creates ANSI-format tar archives. Extracting one of these archives with the old V7 tar can cause warning messages like "tar: unexpected EOF." But, of course, GNU tar has an option to create old-format archives: --old-archive .