calculate tar size

[Raimund Gabriel]

dear tar experts,

 

within a shell script dealing with backup issues utilising a CD recorder, I am facing the problem to calculate the size of a tar archive in advance of its creation (in order to fit into given CD size limitations).

My preliminary observation is, that Gnu tar 1.13.17, invoked with -b1 option, uses two blocks a 512 Byte for the tar file delinmiter containing zeroes only (which is in contrary to the info-file, which states only one block a 512 Byte)! However with self-compiled Gnu tar 1.13, and the same tar option, I find only one block a 512 Bytes for the tar file delimiter used as expected. 

Is there a bug in version 1.13.17, or has there been a change in specification after version 1.13, which is not reflected in the info-file?

I am not fit enough in "c" language to get the full insight from simply looking at the source code, so please help me to solve my problem!

 

Whoever knows more about these details is kindly asked to tell me about how to calculate a tar file size for the various tar versions. 

 

kind regards and thanks for your help in advance,

 

Raimund