Function is_reserved 

pub fn is_reserved(c: i32) -> bool

Check if the given exit code is reserved and has a special meaning in a shells.

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Exit Code	Meaning
0	Success
1	Catchall for general errors
2	Misuse of shell built-ins
64	Usage Error
65	Data Error
66	No Input
67	No User
68	No Host
69	Service Unavailable
70	Software Error
71	OS Error
72	OS File Error
73	Cannot Create
74	IO Error
75	Temporary Failure
76	Protocol Error
77	No Permission
78	Config Error
126	Command invoked cannot execute
127	Command not found
128	Invalid argument to exit
128–137	Fatal error signal (kill -n where n is added to 128)
256+	Exit status out of range
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