bc truncate floating point number
Dividing by 1 works ok if scale
is 0 (eg, if you start bc with bc
and don't change scale
) but fails if scale
is positive (eg, if you start bc with bc -l
or increase scale
). (See transcript below.) For a general solution, use a trunc
function like the following:define trunc(x) { auto s; s=scale; scale=0; x=x/1; scale=s; return x }
Transcript that illustrates how divide by 1 by itself fails in the bc -l
case, but how trunc
function works ok at truncating toward zero:
> bc -lbc 1.06.95[etc...]for (x=-4; x<4; x+=l(2)) { print x,"\t",x/1,"\n"}-4 -4.00000000000000000000-3.30685281944005469059 -3.30685281944005469059-2.61370563888010938118 -2.61370563888010938118-1.92055845832016407177 -1.92055845832016407177-1.22741127776021876236 -1.22741127776021876236-.53426409720027345295 -.53426409720027345295.15888308335967185646 .15888308335967185646.85203026391961716587 .852030263919617165871.54517744447956247528 1.545177444479562475282.23832462503950778469 2.238324625039507784692.93147180559945309410 2.931471805599453094103.62461898615939840351 3.62461898615939840351define trunc(x) { auto s; s=scale; scale=0; x=x/1; scale=s; return x }for (x=-4; x<4; x+=l(2)) { print x,"\t",trunc(x),"\n"}-4 -4-3.30685281944005469059 -3-2.61370563888010938118 -2-1.92055845832016407177 -1-1.22741127776021876236 -1-.53426409720027345295 0.15888308335967185646 0.85203026391961716587 01.54517744447956247528 12.23832462503950778469 22.93147180559945309410 23.62461898615939840351 3
Try the following solution. It will truncate anything after the decimal point without a problem:
echo 'x = 4.2 - 1.3; scale = 0; x / 1' | bc -lecho 'x = l(101) / l(10); scale = 0; x / 1' | bc -l
You can make the code a tad shorter by performing calculations directly on the numbers:
echo 'scale = 0; (4.2 - 1.3) / 1' | bc -lecho 'scale = 0; (l(101) / l(10)) / 1' | bc -l
In general, you can use this function to get only the integer part of a number:
define int(x) { auto s; s = scale; scale = 0; x /= 1; /* This will have the effect of truncating x to its integer value */ scale = s; return (x);}
Save that code into a file (let's call it int.bc) and run the following command:
echo 'int(4.2 - 1.3);' | bc -l int.bc