Handling default values when using getopts t::

Faki · 12-19-2021, 10:11 AM

I have written the following function and want to set a default if user does not supply a value to the option "-t". Haw can I handle this?

Code:

myfunc ()
{
 local nt ng
 local OPTIND OPTARG
 local shortopts=":t::g:"
 while getopts "$shortopts" arg; do
  case $arg in
   ("t") nt=${OPTARG} ;;
   ("g") ng=${OPTARG} ;;
   (*)
      printf "getopts: Error Reporting Mode | Silent "
      printf "arg: $arg"
      case $arg in
       (":")
         printf " No value provided to -${OPTARG} option."
         printf " Give a value, e.g. \"-${OPTARG} 3\"."
         break
         ;;
       ("?")
         printf "User option not dufined in shortopts."
         printf "Invalid -${OPTARG} option provided."
         break
         ;;
      esac
      break
      ;;
  esac    
 done
 printf '%s\n' "nt: $nt | ng: $ng"
}

rtmistler · 12-19-2021, 10:44 AM

Set the variable up in advance and let parsing of options set it, if they use it.

Or check for existence of the variable and use a default if it wasn't defined.

Faki · 12-19-2021, 10:50 AM

Would the default value have to be set after the "while getopts" construct? What happens with "nt=${OPTARG}" if there in no "arg"?

pan64 · 12-19-2021, 10:58 AM

Quote:

Originally Posted by Faki

Would the default value have to be set after the "while getopts" construct?

default should be set before the loop

Quote:

Originally Posted by Faki

What happens with "nt=${OPTARG}" if there in no "arg"?

getopts will set OPTARG if : was specified (or will report an error if that argument was missing). But you can check it yourself. Or see (for example) here: https://www.golinuxcloud.com/bash-getopts/

Faki · 12-19-2021, 12:02 PM

I am still quite unsure about this. I want the default to be nt=0 if the "-t" option is not specified. If it is specified only with "-t" I want to have "nt=1", or use the user defined one if supplied with (e.g. "-t3").

Faki · 12-19-2021, 12:27 PM

Why does this

Code:

myfunc -t -g23 gungadin

produce

Code:

nt: -g23 | ng: 0

pan64 · 12-19-2021, 12:32 PM

because you specified that. -t requires an argument, so -g23 will be taken as an argument to -t, not an option.

Faki · 12-19-2021, 12:45 PM

I have used "t::". Would that not mean that the value is optional?

pan64 · 12-19-2021, 01:55 PM

there is no [reliable] way to decide if the string after -t is the next option or an argument to -t.

Faki · 12-19-2021, 02:00 PM

Does getopts support double colon "::" though? I think there is some program that accepts "::" for optional values but cannot remember if it is "getopts" or not.

pan64 · 12-19-2021, 02:05 PM

:: not supported.
https://unix.stackexchange.com/quest...ts-be-optional
and again: https://www.golinuxcloud.com/bash-getopts/
and again: there is no [reliable] way to decide if the string after an option is the next option or an argument.