bash shell script; bc math error

Question

I am a beginner of bash shell scripting. I am using bc for float type data calculation, but I got the following error. I have tried to search this on-line, but wasn't able to solve this. My simplified code and error are attached below.

aa=1270000000.000000
bb=14000000
cc=-5245200.55453439363590374313
dd=4666666.66666666666666666666
ee=$(echo "$aa-$bb/2-$cc+2.5*$dd" | bc -l)

(standard_in) 1: syntax error

The strange thing is that, the following code seems work.

aa=1.222
bb=2
cc=3.999
dd=4.222222
ee=$(echo "$aa-$bb/2-$cc+2.5*$dd" | bc -l)

This is weird, but I don't know how this happen. Does anyone have any idea about this? Thanks in advance.

I've always liked polish notation. ee=$(dc -e "$aa $bb 2 / - $cc - 2.5 $dd * + p"). — ghoti
– ghoti, Commented Sep 11, 2017 at 18:45

chepner · Accepted Answer · 2017-09-11 18:36:23Z

2

bc's parser treats adjacent negative signs as the decrement operator; 3--3 is not the same as 3 - -3 or 3-(-3). You need to adjust the argument to echo accordingly, to accomodate a value of cc that begins with a -.

ee=$(echo "$aa-$bb/2-($cc)+2.5*$dd" | bc -l)

or

ee=$(echo "$aa - $bb / 2 - $cc + 2.5 * $dd" | bc -l)

edited Sep 11, 2017 at 18:36

answered Sep 11, 2017 at 18:17

chepner

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Comments

fundagain · Accepted Answer · 2017-09-11 18:20:55Z

0

bc needs spaces between operators.

aa=1270000000.000000
bb=14000000
cc=-5245200.55453439363590374313
dd=4666666.66666666666666666666
ee=$(echo "$aa - $bb / 2 - $cc + 2.5 * $dd" | bc -l)

answered Sep 11, 2017 at 18:20

fundagain

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1 Comment

Benjamin W. Over a year ago

This is not generally correct. It only needs spaces to tell 1--2 apart from 1-(-2).

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