[SOLVED] What's the meaning ${1:-}?

Issue

Could you help me explain the expression in BASH script ?

${1:-}

I never see it before, so I try some about it.

echo ${1:-}
echo ${1}

I cant see any difference.

Thank you very much!!!

Solution

Just a small example adapted from here

varName="Aloha"
echo "varName is not empty: the two constructs behave the same"
echo ${varName-Hello World}
echo ${varName:-Hello World}
echo ""
unset varName
echo "varName is unset: they still behave the same way"
echo ${varName-Hello World}
echo ${varName:-Hello World}
echo ""
varName=""
echo "varName is empty: this is where the two differs"
echo ${varName-Hello World}
echo ${varName:-Hello World}
echo ""

Basically :- changes the values of the variable if it's empty or not set, and : changes it if it's not set.

Answered By - random_user

Answer Checked By - Pedro (WPSolving Volunteer)