It looks like bc doesn't support float operations, when I do echo 1/8 | bc it get me a zero.

I checked bc (1), but it doesn't even mention float, so I wonder if it's supported?


bc doesn't do floating point but it does do fixed precision decimal numbers. The -l flag Hauke mentions loads a math library for eg. trig functions but it also means

[...] the default scale is 20

scale is one of a number of "special variables" mentioned in the man page. You can set it:


Anytime you want (whether -l was used or not). It refers to the number of significant digits used in a decimal. In other words, subsequent solutions will be rounded to that number of digits after the decimal scale (== fixed precision).

The default scale sans -l is 0, meaning rounded to whole numbers.

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man page says:

If bc is invoked with the -l option, a math library is preloaded [...]

The comprehensibility of that could be improved, indeed...

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  • 14
    Report it upstream as a bug... – vonbrand Mar 4 '13 at 3:18

1) Numbers in bc have a scale. The scale of a number should not be confused with the scale factor. The same world 'scale' is used as a function to query the scale of a number or as a parameter to set the scale factor.

echo "scale=scale(1.1);11/10" | bc will return 1.1

2) The scale factor determines how many digits are kept to the right of the decimal point when doing operations. If s is the current scale factor, sa is the scale of the first operand a, sb is the scale of the second operand b, results are truncated as follow :

    scale of result
a+b     max(sa,sb)
a-b     max(sa,sb)
a*b     min(sa+sb , max(s,sa,sb))
a/b     s
a%b     so that a = b*quotient + remainder; remainder has sign of a
a^b     min(sa×|b|, max(s,sa)); b must be integer
sqrt(a) max(s,sa)

3) At the origin bc was a preprocessor of dc. Now, on many systems, bc is a standalone program.

Source : [https://plan9.io/magic/man2html/1/dc]

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