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

From: Greg Wooledge
Subject: Re: [Help-bash] ${var:?message} customization
Date: Thu, 14 May 2015 08:23:26 -0400
User-agent: Mutt/

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"

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"
        echo "var is set to a non-empty string"
    echo "var is unset"

(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.)

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