I have a large (binary) file that has some corruption near the beginning.

Then, I have a second, smaller file that I obtain by starting to download the same file again, but interrupt after I have enough bytes to fix the original one.

My question is, how do I simply overwrite the beginning of the large file with the contents of the second, smaller file? I could use cat, tail and head, but that would create a copy of the file. There must be a more efficient way.

Oh yes, and I'm looking for a linux command-line solution, if that wasn't obvious. I'm using bash, but I have other shells if that helps.