Mathematical expression result assigned to a Bash variable

问题

How do I save the result of evaluating a mathematical expression to a variable using bash? My code is the following:

W1=$(bpimagelist -U -d 11/01/2013 00:00:00 -e 11/05/2013 00:00:00 -pt FlashBackup-Windows | tail -n +3 | awk '{s+=$5} END {print s/1024/1024/1024}')    
W2=$(bpimagelist -U -d 11/01/2013 00:00:00 -e 11/05/2013 00:00:00 -pt MS-Windows | tail -n +3 | awk '{s+=$5} END {print s/1024/1024/1024}')

echo "$W1+$W2" | bc | awk '{printf "%.02f\n", $1}' 

Console Output: 96.86

I am looking for a code similar to this:

W="$W1+$W2" | bc | awk '{printf "%.02f\n", $1}'  (not correct syntax though)

Any ideas?

回答1:

 W3=$( echo $W1+$W2 | bc )

... have you tried this?

回答2:

Two options:

1. Use back tics:

   W1=`command`

2. Use parens

   W1=$(command)

Your command can be as complex as what you have above (e.g. multiple commands joined with pipes)

Option 2 allows for nesting of commands, e.g.

W1=$(command1 $(command2))

回答3:

This would work if both W1 and W2 were integers:

(( W = W1 + W2 ))

It seems you may be dealing with floating point numbers, though, so something like this might work in that case:

W="$(bc <<< "${W1} + ${W2}")"

来源：https://stackoverflow.com/questions/20138516/mathematical-expression-result-assigned-to-a-bash-variable