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linuxunix
Muhammad Ali
Muhammad Ali

Reputation: 1

The exit status in Linux shell

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.

Upvotes: 0

Views: 92

Answers (3)

choroba
choroba

Reputation: 242123

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

Upvotes: 1

Embedded Software Engineer
Embedded Software Engineer

Reputation: 4904

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.

Upvotes: 0

wRAR
wRAR

Reputation: 25559

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.

Upvotes: 0

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