Shortest command to calculate the sum of a column of output

Posted 06-02-2010 at 06:27 AM by bittner

I had to calculate the Installed-Size for a .deb control file recently. Here is the solution I came up with:

Code:

dpkg-deb -c mypackage.deb | sed -e 's/.*root\s*//' -e 's/\s*2010-.*$//' | xargs | tr ' ' + | bc

What it does? The code tries to construct a calculation string and feeds it to the command line calculator bc as follows:

use dpkg-deb to get the file size information out of the Debian package
sed away all characters before and after the number on each line (I could also sed away the 0 file sizes with an additional -e '/^0$/d', but that's optional from a mathematical point of view, obviously)
xargs the result (to get a string of numbers separated by blanks)
translate the blanks to '+' characters
use bc to calculate the result

I have posted the same (or similar) solution on StackOverflow, by the way.

Enjoy!

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Usually, bc should be installed on your Debian system. If you don't have it you could simply use a for loop that's built into bash:

Code:

SUM=0; for i in $(dpkg-deb -c mypackage.deb | sed -e 's/.*root\s*//' -e 's/\s*2010-.*$//' | xargs | tr ' ' +); do SUM=$(($SUM+$i)); done; echo $SUM

Or probably easier to read:

Code:

NUMBERS=$(dpkg-deb -c mypackage.deb | sed -e 's/.*root\s*//' -e 's/\s*2010-.*$//' | xargs | tr ' ' +)
SUM=0; for i in $NUMBERS; do SUM=$(($SUM + $i)); done
echo $SUM

You will notice that this takes a while, because the for loop is slow. Here, stripping out the 0-value lines may make sense...

Posted 06-02-2010 at 06:57 AM by bittner bittner is offline

Calculate using Bash when bc is not installed

A much better alternative to bc than using a lengthy for loop is using Bash's calculation capability directly. Interestingly, I've figured out, there are two ways of assigning a value to a variable this way:

(( A=1+1 ))
A=$(( 1+1 ))

The spacing after and before the double-brackets is optional. The above calculation exercise would then read like this:

Code:

((SUM=$(dpkg-deb -c mypackage.deb | sed -e 's/.*root\s*//' -e 's/\s*2010-.*$//' | xargs | tr ' ' +)))

Code:

SUM=$(($(dpkg-deb -c mypackage.deb | sed -e 's/.*root\s*//' -e 's/\s*2010-.*$//' | xargs | tr ' ' +)))

Posted 08-25-2010 at 03:12 AM by bittner bittner is offline