Catch `setopt nounset`

Catch `setopt nounset`

[Thorsten Kampe]

Hi,

I'd to catch the call of a parameter that does not exist with `setopt 
nounset`.

```
setopt nounset

testfunc() {
printf "$DOESNOTEXIST\n"
}

if testfunc
then
    printf "no error\n"
else
    printf "error\n"
fi
```

This does not work. Neither the then nor else clause are entered. If 
I replace the `catch` statement with `if result=$(testfunc)` it 
prints "error". What am I missing here? Why does the latter work but 
not the former?

```
if result=$(testfunc)
then
    printf "no error\n"
else
    printf "error\n"
fi
```

Thorsten

Re: Catch `setopt nounset`

[Bart Schaefer]

On Apr 9,  6:30pm, Thorsten Kampe wrote:
} 
} I'd to catch the call of a parameter that does not exist with `setopt 
} nounset`.

    setopt nounset
    {
      print "$DOESNOTEXIST"
    } always {
      if (( TRY_BLOCK_ERROR ))
      then print "error"
      else print "no error"
      fi
    }

} If I replace the `catch` statement with `if result=$(testfunc)` it 
} prints "error". What am I missing here? Why does the latter work but 
} not the former?

"parameter not set" is a fatal error, so whatever the current shell is
doing is stopped when that happens.  $(testfunc) is run in a subshell,
so the current shell proceeds even though the subshell died.

You could get the same result with

  if ( testfunc )
  then
    printf "no error\n"
  else
    printf "error\n"
  fi

but of course that also suppresses all other side-effects of "testfunc",
which the "always" construct will not.

Re: Catch `setopt nounset`

[Thorsten Kampe]

* Bart Schaefer (Thu, 9 Apr 2015 11:42:05 -0700)
> 
> On Apr 9,  6:30pm, Thorsten Kampe wrote:
> } 
> } I'd to catch the call of a parameter that does not exist with `setopt 
> } nounset`.
> 
>     setopt nounset
>     {
>       print "$DOESNOTEXIST"
>     } always {
>       if (( TRY_BLOCK_ERROR ))
>       then print "error"
>       else print "no error"
>       fi
>     }
> 
> } If I replace the `catch` statement with `if result=$(testfunc)` it 
> } prints "error". What am I missing here? Why does the latter work but 
> } not the former?
> 
> "parameter not set" is a fatal error, so whatever the current shell is
> doing is stopped when that happens.  $(testfunc) is run in a subshell,
> so the current shell proceeds even though the subshell died.

Interesting explanation about the fatal error, subshell and an 
interesting solution as well.

Unfortunately, the code should run in bash and zsh if possible, so I 
went for `printf "$DOESNOTEXIST="` which catches the "`unbound 
variable`/`parameter not set`" fatal error but still generates a 
normal error because of the printf.

Of course the `always` solution is more general, more readable, and 
superior.

Thorsten