What is the point of this: "${STARTED_TMUX:-x}" = x vs. -z "$STARTED_TMUX" or "$STARTED_TMUX" = "" It's always seemed like a legacy method of testin

What is the point of this: "${STARTED_TMUX:-x}" = x vs. -z "$STARTED_TMUX" or "$STARTED_TMUX" = "" It's always seemed like a legacy method of testing to empty string from a time when "" wouldn't be parsed as an argument. Is there any real reason to still do that today?