Git alias:

diff-chunk = "!f() { \
    git show \"\$1:\$3\" | sed -n \"/^[^ \t].*\$4(/,/^}/p\" > .tmp1 ; \
    git show \"\$2:\$3\" | sed -n \"/^[^ \t].*\$4(/,/^}/p\" > .tmp2 ; \
    git diff --no-index .tmp1 .tmp2 ; \
}; f"

Example:

git diff-chunk

Suppose we want to see just the differences of one chunk, such as one function, in one file, in two different commits.

This alias creates two temp files which contain only the chunk, then does a typical git diff.

Syntax:

git diff-chunk <old-rev> <new-rev> <path> <chunk pattern>