Minimal swap file use or deleting only swapfiles without changes

Question

When I lose power, I have a lot of maybe-useful swap files (4 vim instances running now, 103 swap files currently in ~/.cache/vim/swap). I am fine with manual recovery of swapfiles with changes - I'd just like a way to either:

1. delete all lock-only swapfiles post-reboot or other times I know there are no running vim instances
2. minimize the number of lock-only swapfiles to 1 per open instance of vim

I opened an issue on Github to see if vim could manage 2 without any plugins, etc, but unfortunately it was not deemed worthy of support hours.

I request a solution to either 1 or 2 which:

• is easy to remember - short, small, easy to copy-paste between computers
• and is not instructions for the computer to download or call a special dependency - ie, no vim plugins, Java programs, etc. The entire solution needs to be short enough to match the above criterion. So, ie, 5 lines of python/perl/awk/vimscript/etc would be great.

Attempted solutions:

• Haven't found a vim command-line flag to tell me if a swapfile is only a lockfile instead of a recovery file
• Haven't found a vimscript instruction to store lock and recovery files separately.
• Have read the source to 3-4 different vimscript plugins - one removes set hidden on buffer switch, another diffs swap files, another deletes swap files without regard for if they're lock files, etc. None (so far) are simple enough to be easily portable.
• GitHub issue
• rm ~/.cache/vim/swap/* - destroys recovery files along with the lock files

Have not yet tried:

• reading the swap file format to see if there's something I can hook to w/eg grep
• installing/testing various vimscript plugins - not very portable
• setting read-only mode by default, then setting it again when I save a buffer. I'm looking for something I do at most once per boot, not on every file access - if every file access that's why we have software.
• as the above, but w/o set hidden by default

Answer 1

I've often found myself in a similar situation and, this past weekend, wrote the beginnings of a solution. Take a look at the Go library toolman.org/file/viminfo -- with this I'll be able to write a solution for your #1 (or similar), hopefully in the next week or so.

Stay tuned.

Answer 2

In fish syntax: for file in ~/.cache/vim/swap/*; [ (cat "$file" | dd ibs=1 skip=1007 count=1 2> /dev/null) != 'U' ]; and rm "$file"; end; - this works, but seems to me fragile - ie, if the vim swap file format changes, this would fail (and possibly lead to data loss equivalent to removing all swap files).

I didn't bother with this (in the "have not tried yet" section of my question) because I feel it is too risky/fragile, until a comment angered me enough to make it worth the bother to prove that it is, in fact, possible.

I believe there exist other, better solutions. Please help me find one.