Operator Parameter Set and Not Null Parameter Set but Null Parameter Unset
${parameter:-word} substitute parameter substitute word substitute word
${parameter-word} substitute parameter substitute null substitute word
${parameter:=word} substitute parameter assign word assign word
${parameter=word} substitute parameter substitute null assign word
${parameter:?word} substitute parameter error, exit error, exit
${parameter?word} substitute parameter substitute null error, exit
${parameter:+word} substitute word substitute null substitute null
${parameter+word} substitute word substitute word substitute null

References

Last Updated: 2/9/2018, 1:45:45 PM