standard Unix exit codes

UNIX (Symbol)	Exit	Value
EX_OK	0	No errors during session.
EX_USAGE	64	Command line usage error. The command was used incorrectly (wrong number of arguments, bad flag, bad syntax in a parameter, or whatever).
EX_DATAERR	65	Data format error. The user's input data was incorrect in some way.
EX_NOINPUT	66	Cannot open input. User's input file did not exist or was not readable.
EX_NOUSER	67	Addressee unknown. User specified does not exist.
EX_NOHOST	68	Host name unknown. Host specified does not exist. Used in mail addresses or network requests.
EX_UNAVAILABLE	69	Service unavailable. Occurs if a support program or file does not exist. Can be used as a catchall message when not known why something is not working.
EX_SOFTWARE	70	Internal software error inconsistency, etc. in HSI code (non-operating system- related errors).
EX_OSERR	71	Operating system error, such as cannot fork, cannot create pipe, getuid, returning a non-existent user, etc..
EX_OSFILE	72	Critical OS file missing, cannot be opened, or has some sort of error (syntax error).
EX_CANTCREAT	73	Cannot create user output file.
EX_IOERR	74	Input/output error, occurred while doing I/O on some file.
EX_TEMPFAIL	75	Temporary failure. User is invited to retry.
EX_PROTOCOL	76	Remote error in protocol. The remote system returned something that was not possible during a protocol exchange.
EX_NOPERM	77	Permission denied. User did not have sufficient permission to perform the operation.