Читать книгу Linux Bible - Christopher Negus - Страница 205

Although most elements of shell scripts are relatively freeform (where white space, such as spaces or tabs, is insignificant), both let and expr are particular about spacing. The let command insists on no spaces between each operand and the mathematical operator, whereas the syntax of the expr command requires white space between each operand and its operator. In contrast to those, bc isn't picky about spaces, but it can be trickier to use because it does floating-point arithmetic.

To see a complete list of the kinds of arithmetic that you can perform using the let command, type help let at the bash prompt.