Awk Floating Point Number Addition Results Are Unexpected

grep ‘foo’ 2012-2013.txt | awk ‘BEGIN{ sum=0.0}{ sub(“,”,””,$7); sum +=$7}END{ print “$” sum}’
$682444

Example: Awk floating point calculation

The following example uses a file called trade.txt, which contains a list of week names as well as four profit values per week:

week1 12.5 12.5 13.5 18.5
week2 11.5 11.10 12.10 13.70
week3 8.5  8.10 8.5 12.5
week4 9.5 11.5 13.5 16.5
week5 8	7 13 17

The following awk program takes the file trade.txt and prints the sum of all four values:

awk '{ sum = $2 + $3 + $4 + $5; print $1, sum }' trade.txt

Sample outputs:

week1 57
week2 48.4
week3 37.6
week4 51
week5 45

The following awk program takes the file trade.txt and prints the average of all four values:

awk '{ sum = $2 + $3 + $4 + $5; avg = sum/4; print $1, sum , avg}' trade.txt

Sample outputs:

week1 57 14.25
week2 48.4 12.1
week3 37.6 9.4
week4 51 12.75
week5 45 11.25

To avoid surprises use printf to format text to make your output more beautiful and meaningful:

awk '{ sum = $2 + $3 + $4 + $5; avg = sum/4; printf "%s: $%.2f ($%05.2f)\n",$1, sum, avg}' trade.txt

OR

awk '{ sum = $2 + $3 + $4 + $5; avg = sum/4; printf "%s: $%.2f ($%5.2f)\n",$1, sum, avg}' trade.txt

Sample outputs:

week1: $57.00 ($14.25)
week2: $48.40 ($12.10)
week3: $37.60 ($ 9.40)
week4: $51.00 ($12.75)
week5: $45.00 ($11.25)

To fix your problem, replace the following awk code

grep 'foo' 2012-2013.txt  | awk 'BEGIN{ sum=0.0}{ sub(",","",$7); sum +=$7}END{ print "$" sum}'

with:

grep 'foo' 2012-2013.txt  | awk 'BEGIN{ sum=0.0}{ sub(",","",$7); sum +=$7}END{  printf "$%.2f\n", sum}'

You can skip the grep command and use awk as follows to match and perform sum of all $7:

awk '/foo/{ sub(",","",$7); sum = old + $7; old=sum}END{ printf "$%.2f\n", sum}' 2013-2014.txt

Recommended readings

• See awk command man page for more info.