Bash Variable Expansion

This is one of those things that just doesn't stick in my head, so I'm dropping this note to remind myself. I often have trouble recalling cryptic variable names in bash, make, and perl. For my own sake, I thought I'd make a quick list of favorites and refer some sources. Maybe you'll find this useful too. Variable value, but exit if no such variable: ${var:?"error message"} Use default if…