Checking if the first argument passed to a bash script is set?

Question

I'm attempting to see whether the first argument passed to my script is set. I used the instructions found here to create a test: How to check if a variable is set in Bash?

Here's my script:

var=$1
if [ -z ${var+x} ]; then echo "var is unset"; else echo "var is set to '$var'"; fi

Suppose I run it without any arguments:

ole@MKI:./test.sh
var is set to ''

Suppose I run it with an argument:

ole@MKI:./test.sh foo
var is set to 'foo'

In neither case does it report that the var is unset.

Thoughts?

TIA, Ole

Answer 1

The problem is with this line:

var=$1

This sets var and it does so regardless of whether $1 is set or not. The solution is to test $1 :

if [ -z ${1+x} ]; then echo "var is unset"; else echo "var is set to '$1'"; fi

This approach works:

$ test.sh
var is unset
$ test.sh a
var is set to 'a'

Answer 2

Even if no parameter is provided when the script is run, the var variable is set. It is assigned the empty string.

The shell also set the $# special parameter to the number of parameters.

Give a try to this:

if [[ $# = 0 ]] ; then printf "no parameter\n"; exit 1; else printf "At least one parameter\n"; var="${1}"; fi

If you go ahead with other additional parameters such as options, then you may consider to use the getopts - parse utility options - from The Open Group Base Specifications Issue 7