float Point math in Unix shell script and assign it to variable

Question

I have been doing integer calculation like this.

a=12
b=23
c=$((a-b))
echo $c

But, now for float numbers its is failing i read that we can do that using bc however i want to assign the result in variable at the end.

a=12.7
b=23.33
c=$((a-b)) | bc
echo $c

Kusalananda · Accepted Answer · 2018-03-02T16:12:18.787

5

c=$( printf '%s - %s\n' "$a" "$b" | bc )

or, for the lazy,

c=$( echo "$a - $b" | bc )

or, for the lazy bash user,

c=$( bc <<<"$a - $b" )

The issue with your code is that

c=$((a-b)) | bc

won't work. You can only (usefully) pipe things that produces output, and c=$((a-b)) is an assignment that 1) will fail if $a or $b are floating point numbers (with a syntax error), and 2) does not produce output. Furthermore, the output from bc (nothing) will not be assigned to c since it's not part of the assignment at all.

edited Mar 02 '18 at 16:12

answered Feb 28 '18 at 20:57

Kusalananda

333,661

if you can help me with floating number comparison also , will be awesome.I am trying to do
if [ bc <<< "$c -gt 0"] then .... fi
– Avitesh Kesharwani Mar 02 '18 at 16:15
@AviteshKesharwani That's a new question though. – Kusalananda Mar 02 '18 at 16:15

float Point math in Unix shell script and assign it to variable

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