bc is ignoring scale option

问题:

I can't figure out why bc tool sometimes ignores the scale option.

Here is an example:

> echo 'scale=2; 2.777 - 1.4744' | bc
1.3026

Expected result is:

1.30

Additional information:

> bash --version
GNU bash, version 2.05b.0(1)-release (x86_64-suse-linux)
Copyright (C) 2002 Free Software Foundation, Inc.
> bc --version
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.

回答1:

as Carl pointed out, if you check man page, you can find that line. it is about expression explanations. subtraction won't read scale variable. If you want to get the expected result (1.30), you could:

kent$  echo 'scale=2; (2.777 - 1.4744)/1' | bc 
1.30

/ operation will read scale variable.

回答2:

From the bc(1) man page:

Unless specifically mentioned the scale of the result is the maximum scale of the expressions involved.

1.4744 has scale 4, so that's what happens to your expression.