Value returned by a simple order (128 + n)

A signal is different from an exit status. Now, what of the number 128 I think is (without references) by 256 (of the available output states) between 2. That would be the shell where it runs and a subshell from where the signal less than or equal to 128 is issued.

For example.

$ export senial
$ for senial in {1..15}
for> do
for> bash -c 'bash -c "kill -$senial \$\$"; echo "$?"' 2> /dev/null
for> done
129
130
0
132
133
134
135
136
137
138
139
140
141
142
143

And it shows me your exit status as the exit status 128 + the signal .

If you include the range {1..123} in the for, you see that the output state is according to the formula described, but until the signal 32. Then, in the range of [32-64], the output is of 0, then, the output is a general error, that is equal to 1.

Perhaps by writing, @mrc_es, you understood that it did not differentiate between the output state and the signal.
In case anyone who arrives here helps you:
The exit status "determines the destination of the result of a program or process, by default it is the screen and the result of a program or process, by default it is the screen and the result is displayed in the terminal console, although it can be redirected to a file ". Or to other "places", I add, like the bottomless sack / dev / null ...
I have not found a better definition of signal than "an asynchronous notification or event that one process sends to another".
Yes I have been able to read that there are up to 256 signals available in GNU / Linux, and, in fact, Appendix E of the Advanced Bash-Scripting Guide ( link ) (Codes with special meanings) manifests:

  

exit codes 1 - 2, 126 - 165, and 255 [1] have special meanings, and should there be avoided for user-specified exit parameters.
  [...]   
  There has been an attempt to systematize exit status numbers (see / usr / include / s andsexits.h), but this is intended for C and C ++ programmers. A similar standard for scripting might be appropriate.
  [...]
  [1] Out of range exit values can result in unexpected exit codes.
  An exit value greater than 255 returns an exit code module 256. For example, exit 3809 gives an exit code of 225 (3809% 256 = 225).

Again from my absolute ignorance, and without a source I can cite, I dare to venture that, at the kernel level, any signal is sent as a single bit, which would allow a maximum of 256 signals (2 raised to 8). Another thing is that there is a definite meaning for each of them: the man signal is illustrative about it.
Thanks again, @mrc_es.
PS: I have dared to answer my own question, being supported in little more than my own logic, because in commentaries all this does not enter, by limit of characters.