qalc
Powerful and easy to use calculator. tldr-pages
On several platforms
Several platforms
Launch in interactive mode
qalc --interactiveIdentifyLaunch in terse mode (print the results only)
qalc --terseIdentifyUpdate currency exchange rates
qalc --exratesIdentifyPerform calculations non-interactively
qalc 66+99|2^4|6 feet to cm|1 bitcoin to USD|20 kmph to mph|...IdentifyList all supported functions/prefixes/units/variables
qalc --list-functionsIdentifyExecute commands from a file
qalc --file path/to/fileIdentify