Rewrite git history to modify a file -

to remove large unwanted file of git history can use filter-branch rewrite index (the list of files in repo) of each commit file never added.

git filter-branch --index-filter "git rm --cached --ignore-unmatch path/to/offending_file.wav" --tag-name-filter cat -- --all 

but if want keep file make lot smaller (e.g. imagine if icon accidentally stored huge image). tried approach:

first add replacement file git's database

hash=`git hash-object -w /tmp/replacement.png` 

also note file want replace

file="path/to/icon.png" 

now filter index follows: first check file exists @ commit:

git cat-file -e :"$file" 

if remove index:

git rm --cached "$file" 

and add reference our replacement same filename.

git update-index --add --cacheinfo "100644,$hash,$file" 

putting together:

git filter-branch --index-filter "if git cat-file -e :$file ; git rm --cached $file ; git update-index --add --cacheinfo 100644,$hash,$file ; fi" --tag-name-filter cat -- --all 

this seems work , doesn't print errors too scary. however, no matter how many git gc , prune commands try original blob still exists in repository. if clone repo new place still exists.

i suspect because remote refs, , original refs filter-branch creates still point old tree, original file still referenced.

i did try removing them hack this:

for ref in `git show-ref | cut -c 42- | grep original` ; git update-ref -d $ref ; done 

and same remotes, blob still there.

so questions:

1. is there way see why blob isn't garbage collected? i.e. parents objects in graph point it?
2. is there non-hacky way remove originals refs (and maybe remotes) - including branches , tags?
3. is there else i'm missing?

aha i've done it! think.

here steps. first it's idea note hash of blob want @ start can check if exists with

git cat-file -t 949abcd.... 

ok first cleared reflog, since still has reference original clone:

git reflog expire --expire=now --all 

next removed origin remote, since still has reference original tree. guess if push new hashes (probably need force push) step unnecessary , file should gced anyway.

git remote rm origin 

next removed original refs (that filter-branch creates). didn't find less hacky way:

for ref in `git show-ref | cut -c 42- | grep original` ; git update-ref -d $ref ; done 

finally, garbage collect. i'm not sure whether --aggressive required --prune=now because otherwise git gc garbage collects old unwanted objects, safety.

git gc --aggressive --prune=now 

after these steps git cat-file reports blob gone! haven't experimented pushing result origin (after re-add it), , i'm not 100% sure of above steps necessary, seemed work far.