I was working with Eagle 4.16r2 (Yes I know its old), and when I work on my project in it, I happen to save my work frequently as files with extensions .brd and .sch.

I just did a backup and now I see a ton of files which I did not create. The core name is the same name I used but the extensions are .s#n and .b#n where n is a number (and '#' is actually in the extension), and it seems each of these files that are created roughly are the same size in disk space as the ones with the proper extensions.

In the program itself when I'm browsing for the files, only the files with the proper extensions are listed.

So is it always safe to delete files with extensions containing non-alphanumeric characters?

  • 7
    Pretty sure numbers are alphanumeric... Apr 3, 2018 at 12:57
  • 11
    @JamesHughes But the # is not. I was confused at first reading the question too :-) The # is not a place-holder for a number in this case. The number follows the # character.
    – Tonny
    Apr 3, 2018 at 13:08
  • Ahh... My mistake Apr 3, 2018 at 14:47

3 Answers 3


No, temporary file handling is entirely determined by the application that manages the files; there are no rules or even conventions across apps.

  • 6
    mp3 is alphanumeric. OP is asking about non-alphanumeric, i.e: .💩
    – ILikeTacos
    Apr 3, 2018 at 13:46
  • 17
    @ILikeTacos Although unsanitary, you can touch 💩 on modern OSes without any problem. Don't forget to wash your hands !
    – Aaron
    Apr 3, 2018 at 15:03
  • Edited to remove reference to MP3. The core message remains; apps handle their types themselves, and there are no rules that allow assumptions like the one the OP would like to make. Apr 4, 2018 at 14:43

Not in general. In case of Eagle .b#1 and .s#1 files are created when you save your design, so they are backups. You can delete them.


Yes. It's and you can delete them, if you know the name pattern rules. And it happens that you know them.

If you are convinced that you can delete these files, not causing side effects in the application that created them, you have some command line options:

Bash (Windows, Linux, or OSX) - The most precise way, there are no risks of deleting files like xxx.s#aa (letters instead of numbers on the last 2 characters) ls *.s#?? *.b#?? | grep '[0-9][0-9]$' | xargs rm

Bash (Windows, Linux, or OSX) - Any character (instead of only numeric characters): rm *.s#?? *.b#??

Windows - Any character (instead of only numeric characters): del *.s#?? del *.b#??

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