You exclude *.bak and *.tmp files as of WinMerge 2.16.19
In 2.16.19 and later, if you put an exclamation mark(!) in front of a mask, files matching that mask will be excluded. Also, a backslash(\) after the mask will cause the mask to match folders instead of files.
Example 2. Excluding folders (In 2.16.19 or later)
In this command-line example, the folder compare operation excludes .git and .vs folders:
WinMergeU c:\project\docs c:\temp /f !.git;!.vs
Use this filter:
*.*;f:!*.bak;f:!*.tmp
After adding it, you'll be able to exclude *.bak and *.tmp files.
PS L:\temp\winmerge> Get-ChildItem .\folder1\
Directory: L:\temp\winmerge\folder1
Mode LastWriteTime Length Name
-a---- 4/30/2023 8:19 PM 0 file1.txt
-a---- 4/30/2023 8:19 PM 0 file2.bak
-a---- 4/30/2023 8:19 PM 0 file3.tmp
PS L:\temp\winmerge> Get-ChildItem .\folder2\
Directory: L:\temp\winmerge\folder2
Mode LastWriteTime Length Name
-a---- 4/30/2023 8:19 PM 0 file1.txt
-a---- 4/30/2023 8:19 PM 0 file2.bak
-a---- 4/30/2023 8:19 PM 0 file3.tmp
*.bak and *.tmp files will be skipped. Example Winmerge output here
file1.txt Text files are identical 4/30/2023 8:19:05 PM 4/30/2023 8:19:05 PM txt
file2.bak File skipped 4/30/2023 8:19:05 PM 4/30/2023 8:19:05 PM bak
file3.tmp File skipped 4/30/2023 8:19:05 PM 4/30/2023 8:19:05 PM tmp