git merge, keep both

There is no 'merge strategy' for resolving these conflicts.

However, if you truly want a conflict like:

<<<< ours
Foo
=========
Bar 
>>>> theirs

to resolve to

Foo
Bar

then you can configure the 'merge driver'. From the gitattributes man page:

union

Run 3-way file level merge for text files, but take lines from both versions, instead of leaving conflict markers. This tends to leave the added lines in the resulting file in random order and the user should verify the result. Do not use this if you do not understand the implications.

Add a line to .gitattributes to use this:

*.whatever merge=union

What about this one?

grep -v -e'^<<<<<<<' -e '^>>>>>>>' -e'=======' filename.txt > filename.tmp

mv filename.tmp filename.txt