Lifted/slightly customized from Kenneth Kalmer's post on his blog, Open Sourcery: Pluck out an old revision of a file with git show
• Find the offending commit with 'git lg', 'git log' or 'git log -p'.
• View the file in question by:
git show SHA-ID:path/to/file
or if you're using a text editor with CLI hooks- something like this:
git show SHA-ID:path/to/file | text-editor-hook
for example, I call Sublime Text 3 from the terminal via the 'slime' command, so I would:
git show SHA-ID:path/to/file | slime
and, presto! the file appears in Sublime Text.
• Replace current copy with:
git show SHA-ID:path/to/file > path/to/file
or if you went the text editor route, then just copy the offending lines to the current file, in the text editor.
• Verify the damage has been undone with 'git diff'