Lets say you like to use the Linux shell for totaling up your calories. Maybe you've got a file something like this:
590soft beef tacos
You could manually calculate these or... you could use some nifty Linux programs. First lets get those numbers away from the rest of the file.
cat 20140211.calories | cut -f 1
cut uses as the default delimiter and we want the first field.
Now you've got the numbers but they are not in a usable math expression so you can use "paste"
cat 20140211.calories | cut -f 1 | paste -s -d+
now you just need to total it all up with "bc"
ExplainShell.com can give a complete break down:
cut -f 1 | paste -s -d+ | bc