about the unix command expand/unexpand

[He Rui]

hi,

During the process of my project, I found something strange related to the 
unix command expand/unexpand. when I expand a text file and then unexpand 
the just expanded file, the unexpand result is not the same as the exact 
original text file. I wonder if the expand/unexpand command are 
intentionally design to have such attribution, 'cauz with my self-developed 
expand/unexpand command, the file remain the same after first expanded and 
then unexpanded.

Below attached the output of unix command expand/unexpand run on a text file 
called test.txt, for your reference.

Look forward to your reply. Thanks,
Rui

=========================
sisko> cat -v -t test.txt
aaaaaaa^Ibbb
sisko> expand -8 test.txt > temp1.txt
sisko> cat -v -t temp1.txt
aaaaaaa bbb
sisko> unexpand -8 -a temp1.txt > temp2.txt
sisko> diff test.txt temp2.txt
1c1
< aaaaaaa       bbb
---
> aaaaaaa bbb
sisko> cat -v -t test.txt
aaaaaaa^Ibbb
sisko> cat -v -t temp2.txt
aaaaaaa bbb

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