Read sysexits FreeBSD manual page to learn how to use consistent exit codes in shell scripts.

SYSEXITS(3)        FreeBSD Library Functions Manual      SYSEXITS(3)

     sysexits -- preferable exit codes for programs

     #include <sysexits.h>

     According to style(9), it is not a good practice to call exit(3) with ar-
     bitrary values to indicate a failure condition when ending a program.
     Instead, the pre-defined exit codes from sysexits should be used, so the
     caller of the process can get a rough estimation about the failure class
     without looking up the source code.

     The successful exit is always indicated by a status of 0, or EX_OK.  Er-
     ror numbers begin at EX__BASE to reduce the possibility of clashing with
     other exit statuses that random programs may already return.  The meaning
     of the codes is approximately as follows:

     EX_USAGE (64)     The command was used incorrectly, e.g., with the
         wrong number of arguments, a bad flag, a bad syntax
         in a parameter, or whatever.

     EX_DATAERR (65)     The input data was incorrect in some way.  This
         should only be used for user';s data and not system

     EX_NOINPUT (66)     An input file (not a system file) did not exist or
         was not readable.  This could also include errors
         like "No message" to a mailer (if it cared to catch

     EX_NOUSER (67)    The user specified did not exist.  This might be
         used for mail addresses or remote logins.

     EX_NOHOST (68)    The host specified did not exist.  This is used in
         mail addresses or network requests.

     EX_UNAVAILABLE (69)   A service is unavailable.  This can occur if a sup-
         port program or file does not exist.  This can also
         be used as a catchall message when something you
         wanted to do does not work, but you do not know

     EX_SOFTWARE (70)    An internal software error has been detected.  This
         should be limited to non-operating system related
         errors as possible.

     EX_OSERR (71)     An operating system error has been detected.  This
         is intended to be used for such things as "cannot
         fork", "cannot create pipe", or the like.  It in-
         cludes things like getuid returning a user that
         does not exist in the passwd file.

     EX_OSFILE (72)    Some system file (e.g., /etc/passwd,
         /var/run/, etc.) does not exist, cannot
         be opened, or has some sort of error (e.g., syntax

     EX_CANTCREAT (73)     A (user specified) output file cannot be created.

     EX_IOERR (74)     An error occurred while doing I/O on some file.

     EX_TEMPFAIL (75)    Temporary failure, indicating something that is not
         really an error.  In sendmail, this means that a
         mailer (e.g.) could not create a connection, and
         the request should be reattempted later.

     EX_PROTOCOL (76)    The remote system returned something that was "not
         possible" during a protocol exchange.

     EX_NOPERM (77)    You did not have sufficient permission to perform
         the operation.  This is not intended for file sys-
         tem problems, which should use EX_NOINPUT or
         EX_CANTCREAT, but rather for higher level permis-

     EX_CONFIG (78)    Something was found in an unconfigured or miscon-
         figured state.

     The numerical values corresponding to the symbolical ones are given in
     parenthesis for easy reference.

     err(3), exit(3), style(9)

     The sysexits file appeared somewhere after 4.3BSD.

     This manual page was written by Jorg Wunsch after the comments in

     The choice of an appropriate exit value is often ambiguous.

FreeBSD 13.0           January 21, 2010       FreeBSD 13.0

This is simply amazing!

PDF files for style.0 and sysexits.0 manual pages (4th November 2021).