example code of Unix bless command

Need Unix example code for using “bless”.

Present situation
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Apple downloads a “Mavericks” operating system to my 128-GB thumb drive.

This download takes anywhere from 5-hours to 14-hours

Resulting thumb drive is bootable, no problem, happy user.

I then create a backup of the entire thumb drive using Apple’s “Time Machine” application.

Problem:   Restored thumb drive is no longer bootable, therefore is useless.

This ONLY happens with the physically small thumb drives.

Keep in mind that when Apple downloads their Mavericks OS to the same thumb drive, the drive is bootable, no problem.   If Apple can force the thumb drive to be bootable, then we should be able to also.

If instead of a thumb drive, I use a larger SSD, the physically larger drive does NOT lose its ability to be bootable after being restored by a Time Machine backup.


Question
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Is it possible to use Unix “bless” to restore a thumb drives bootable characteristic?

My Unix knowledge is extremely weak, so the “man bless” command is gibberish to me.

I know how to use a few Unix commands, like:   diskutil list
and even:  diskutil partitionDisk disk1 2 JHFS+ MAIL-2 42949672960b JHFS+ UNUSED_AA 1048576b


Could some expert please supply some example code of a bless command?

I might be able to puzzle out how to use “bless” from the example code.

Possibly some example like:     bless  disk2  MyThumb  setBoot

( I don’t have the nerve to try the above example, for fear of omitting essential info’ )


My Setup
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MacBook Pro computer running latest “Mavericks” OS.

Bootable external drives, both the spinning mechanical types and the SSD types.