The exit status in Linux shell

Question

why the exit status in Linux/shell i.e in $? is 128 plus the status number. I have searched but couldn't find proper explanation.

It's usually 128 + the signal number. – choroba Mar 14 '16 at 11:49 — choroba, Mar 14 '16 at 11:49

score 1 · Answer 1 · answered Mar 14 '16 at 11:53

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If the exit status is > 127, it's usually the signal number plus 128. The reason is the signal occupies the highest bit in the binary representation of the status.

E.g. 130:

10000010
^     ^
|     |
|     2, i.e. SIGINT
killed by a signal

answered Mar 14 '16 at 11:53

choroba

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score 0 · Answer 2 · answered Mar 14 '16 at 11:50

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Here is the excerpt from bash(1):

The return value of a simple command is its exit status, or 128+n if the command is terminated by signal n.

answered Mar 14 '16 at 11:50

wRAR

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score 0 · Answer 3 · edited May 23 '17 at 11:59

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The return value in POSIX compatible systems is only 1 byte = 8 bits = 255 possible values. Unless you find an odd system that supports more than that, you should pick a different set of values.

You can take a look on this question for more details on returned standards code.

edited May 23 '17 at 11:59

Community

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answered Mar 14 '16 at 11:52

developer

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The exit status in Linux shell

3 Answers3