errno value lister for programmers

errno [option|errorcode|errorname]...
  errno(1) program. When called without arguments it will print a list 
  of all errno values that exist in the system (in reverse order to 
  see the lowest numbers last on screen). Any number or name given 
  will print the errno value record for it which includes the numeric 
  value, the symbolic name, and the strerror description. ... This 
  program is handy for programmers to pick an apropriate errno value 
  when developing software that returns error codes via errno(3) 
   
example: 
    $ errno 11 
    11 EAGAIN       +Resource temporarily unavailable 
  ... so this has looked into the list of errno codes, seen a first 
  matching entry being #define EAGAIN 11, checked that this is a 
  posix-defined errno-code (marking it with '+') and ask strerror(3) 
  for the string message that is usually given for this errno code. 
    $ errno EREMCHG 
    78 EREMCHG       Remote address changed 
  ... so the symbolic code EREMCHG has the code 78 and when a user 
  will check this code with strerror(3) then the given message will 
  be presented as a result. The programmer can now choose whether this 
  is an appropriate message interpolation for the error condition that 
  shall be desribed with an errno code. 
   
return value: 
         it returns 0 on success and a cummulative sum of errors  
         when there were errors during execution
some options: 
   --help      this help screen
   --version   show package name and version number
   --stdout    print to stdout (default)
   --stderr    print to stderr