I have a file that I would like to update, line by line. This is what I'm attempting, which is not working.

open(DATA, "+<myfile.csv") || die "Error: $!";

while(<DATA>) {
    s/foo/bar/g;
    # print;
}

close(DATA);
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If I uncomment #print, the output gives me exactly what I expect, but the file is not updating. What am I missing here? I need to update the file line by line because the file may be extremely large and I do not want to pull the whole thing into memory.