Idiomatic bash: set default value for variable [duplicate]

Question

How can I set a default value for a bash variable in a concise, idiomatic way? This just looks ugly:

if [[ ! -z "$1" ]]; then
    option="$1"
else
    option="default"
fi

Answer 1

default value               : ${parameter:-word} \
assign default value        : ${parameter:=word}  |_ / if unset or null -
error if empty/unset        : ${parameter:?mesg}  |  \ use no ":" for unset only
use word unless empty/unset : ${parameter:+word} /

Answer 2

You can use:

option=${1:-default}

This sets option to the first command line parameter if a first command line parameter was given and not null. Otherwise, it sets option to default. See Bash reference manual for the details on parameter expansion and some useful variants of this form.