// denisdefreyne.com / notes
Last revised:
May 2021
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Standard exit codes

sysexits.h defines standard exit codes:

EX_OK           0       /* successful termination */
EX__BASE        64      /* base value for error messages */
EX_USAGE        64      /* command line usage error */
EX_DATAERR      65      /* data format error */
EX_NOINPUT      66      /* cannot open input */    
EX_NOUSER       67      /* addressee unknown */    
EX_NOHOST       68      /* host name unknown */
EX_UNAVAILABLE  69      /* service unavailable */
EX_SOFTWARE     70      /* internal software error */
EX_OSERR        71      /* system error (e.g., can't fork) */
EX_OSFILE       72      /* critical OS file missing */
EX_CANTCREAT    73      /* can't create (user) output file */
EX_IOERR        74      /* input/output error */
EX_TEMPFAIL     75      /* temp failure; user is invited to retry */
EX_PROTOCOL     76      /* remote error in protocol */
EX_NOPERM       77      /* permission denied */
EX_CONFIG       78      /* configuration error */

Whether or not it is useful to stick to this convention is unclear.