Calculate sum of several sizes of files in Bash

Use stat instead of du:

#!/bin/bash

for i in `grep -v ^# ~/cache_temp | grep -v "dovecot.index.cache"`; do
     [ -f "$i" ] && totalsize=$[totalsize + $(stat -c "%s" "$i")]
done
echo totalsize: $totalsize bytes

According to du(1), there is a -c option whose purpose is to produce the grand total.

% du -chs * /etc/passwd
92K ABOUT-NLS
196K    NEWS
12K README
48K THANKS
8,0K    TODO
4,0K    /etc/passwd
360K    total

If you need to use the file this snippet is hopefully efficient.

xargs -a cache_file stat --format="%s" | paste -sd+ | bc -l

The xargs is to prevent overflowing the argument limit but getting the max number of files into one invocation of stat each time.