Disk usage of files whose names match a regex, in Linux?

Question

So, in many situations I wanted a way to know how much of my disk space is used by what, so I know what to get rid of, convert to another format, store elsewhere (such as da

Answer 1

The accepted reply suggests to use

find . -regex '.*\.bak' -print0 | du --files0-from=- -ch | tail -1

but that doesn't work on my system as du doesn't know a --files-0-from option on my system. Only GNU du knows that option, it's neither part of the POSIX Standard (so you won't find it in FreeBSD or macOS), nor will you find it on BusyBox based Linux systems (e.g. most embedded Linux systems) or any other Linux system that does not use the GNU du version.

Then there's a reply suggesting to use:

find path/to/directory -iregex .*\.bak$ -exec du -csh '{}' + | tail -1

This solution will work as long as there aren't too many files found, as + means that find will try call du with as many hits as possible in a single call, however, there might be a maximum number of arguments (N) a system supports and if there are more hits than this value, find will call du multiple times, splitting the hits into groups smaller than or equal to N items each and this case the result will be wrong and only show the size of the last du call.

Finally there is an answer using stat and awk, which is a nice way to do it, but it relies on shell globbing in a way that only Bash 4.x or later supports. It will not work with older versions and if it works with other shells is unpredictable.

A POSIX conform solution (works on Linux, macOS and any BSD variants), that doesn't suffer by any limitation and that will surely work with every shell would be:

find . -regex '.*\.bak' -exec stat -f "%z" {} \; | awk '{s += $1} END {print s}'