Question

I am writing a bash shell script, run where the user is expected to pass a path into it as the $1 variable. How can I determine if $1 is missing and define a default value instead for it?

Answer 1

You can check the length of the variable.

if [[ -z $1 ]]; then
    echo '$1 is zero-length. Please provide a value!'
fi

If you just want to use a default value, you can use a brace expansion.

first_param=${1:-defaultvalue}

The ${varname:-foo} construct will use the value of varname if it is set, or use what follows the :- if it is not set.