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

I suggest something like: find . -regex '.*\.bak' -print0 | du --files0-from=- -ch | tail -1

Some notes:

• The -print0 option for find and --files0-from for du are there to avoid issues with whitespace in file names
• The regular expression is matched against the whole path, e.g. ./dir1/subdir2/file.bak, not just file.bak, so if you modify it, take that into account
• I used h flag for du to produce a “human-readable” format but if you want to parse the output, you may be better off with k (always use kilobytes)
• If you remove the tail command, you will additionally see the sizes of particular files and directories

Sidenote: a nice GUI tool for finding out who ate your disk space is FileLight. It doesn’t do regexes, but is very handy for finding big directories or files clogging your disk.