expr
Unix-like operating system command
expr is a command line utility on Unix and Unix-like operating systems which evaluates an expression and outputs the corresponding value. It first appeared in Unix v7. The command is available for Microsoft Windows as part of the UnxUtils... Wikipedia
Function: Evaluate expression and print the result to the standard output
Syntax: expr EXPRESSION
Example: expr //$a : '.*/\(.*\)'
Initial release: 1979; 45 years ago