Is there a way to determine the decompressed size of a .bz2 file?

Question

Is there a way to print the decompressed size of a .bz2 file without actually decompressing the entire thing?

Answer 1

As noted by others, bzip2 doesn't provide much information. But this technique works -- you will have to decompress the file, but you won't have to write the decompressed data to disk, which may be a "good enough" solution for you:

$ ls -l foo.bz2
-rw-r--r-- 1 ~quack ~quack 2364418 Jul  4 11:15 foo.bz2

$ bzcat foo.bz2 | wc -c         # bzcat decompresses to stdout, wc -c counts bytes
2928640                         # number of bytes of decompressed data

You can pipe that output into something else to give you a human-readable form:

$ ls -lh foo.bz2
-rw-r--r-- 1 quack quack 2.3M Jul  4 11:15 foo.bz2

$ bzcat foo.bz2 | wc -c | perl -lne 'printf("%.2fM\n", $_/1024/1024)'
2.79M

Answer 2

Given the fact that bzip2 can compress a stream, it means that it doesn't write in the output file a header with the original size. Of course, it could write something at the end of the output, but I doubt it.

Answer 3

The program bzip2 unfortunately doesn't have a list parameter.

If a programmer, I suppose you would need to use libbzip2 to write a small program for doing it.