A proposal for file extension of back up files

There are several extensions used for backup files: 

• .0, .1, etc.
• .old, 
• .bak, 
• .backup, 
• .bkp, 
• ~ suffix
• .orig
• .save
  
• .baka, etc. 
  

Based on Reddit votes, the most used is .bak; therefore, we should use the extension used by common sense.

(Proposed) Specification:

1. A backup file must be named with the extension .bak
2. If there are multiple backups, the next backup extension must be added with an integer, e.g., .bak1, .bak2, etc.
3. The above rules also apply for folder or directory, e.g., folderA.bak, dirB.bak1.

Finding all backup files

To find all backup files, simply use a shell command

$ ls *.bak*
a.bak  a.bak0  a.bak1  a.bak2


Update: 

• 2026/03/23: Sometimes, I found adding .0, .1, is simpler and shorter.