I am trying to unzip bz2 file but then I get the error saying No space left

It's a big world ;-) The error is reasonable.

From https://wiki.openstreetmap.org/wiki/Planet.osm:

on 2021-02-01, the plain OSM XML variant takes over 1370.5 GB when uncompressed from the 99.3 GB bzip2-compressed downloaded data file).

You could ...

• get more disk space
• download osm files for only the regions you really need
• for small regions, use the API.
• use osmosis to extract the needed data from the planet.osm file yourself. But instead of the .bz2 file, you should use the pbf version , which will be much faster.

With some time you could figure out how big the files in the archive are, from the archive file itself.

-rw------- 1 criggie criggie 95M Jul 22  2015 home-email.tar.bz2

$ bzcat home-email.tar.bz2 | wc -c 
149606400

So that 95 MB archive expanded to 149,606,400 bytes in one tar file, which is enough info for your purposes.

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In the unix world, compression can be a different process to archiving, which is why we have gzip and bzip2, and separately have tar for sticking things together.

You could dig inside an expanded tar file with test and verbose flags

$ bzcat home-email.tar.bz2 | tar -tv
...big list of output....

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An archiver/compressor like zip combines the two functions, so had your archive been a zip or an arc or a lhz etc that originated in the PC world, you would have to check the flags for a LIST option - example :

$ unzip -lv /home/criggie/config.zip
Archive:  /home/criggie/config.zip
 Length   Method    Size  Cmpr    Date    Time   CRC-32   Name
--------  ------  ------- ---- ---------- ----- --------  ----
       0  Stored        0   0% 2020-07-28 17:04 00000000  dir/
    1708  Defl:N     1093  36% 2017-02-15 14:15 7c7aee5a  dir/file1.txt
    5354  Defl:N     2860  47% 2020-03-10 15:57 31be4459  dir/file2.txt
--------          -------  ---                            -------
  319022            10362  26%                            20 files