Re: [Help-bash] ${var:?message} customization

[Greg Wooledge]

On Wed, May 13, 2015 at 08:54:09PM -0300, Matias A. Fonzo wrote:
> Normally, "${var:?'message'}" display error if null or unset if
> 'message' is omitted. But if it is not, a particular message can be
> included, in any case, shows (e.g):
> 
>   myscript: line 2: var: parameter null or not set
> 
> My question is, there is a way to print only the message? (removing
> myscript: line number: var:)

Are you just asking "How can I write a message if a variable is unset,
or set to an empty string?"

if [ -z "$var" ]; then
    echo "var is either empty or unset"
fi

If you want to distinguish between "unset" and "set to an empty string",
you can use a more subtle test:

if [ "${var+defined}" ]; then
    if [ -z "$var" ]; then
        echo "var is set to an empty string"
    else
        echo "var is set to a non-empty string"
    fi
else
    echo "var is unset"
fi

(That's all using POSIX sh syntax.  Recent versions of bash have a
"test -v" command, but I don't think it adds much utility.)