Merge two large CSV files with PHP

Question

I want to merge two large CSV files with PHP. This files are too big to even put into memory all at once. In pseudocode, I can think of something like this:

for i in file1
  file3.write(file1.line(i) + ',' + file2.line(i))
end

But when I'm looping through a file using fgetcsv, it's not really clear how I would grab line n from a certain file without loading the whole thing into memory first.

Any ideas?

Edit: I forgot to mention that each of the two files has the same number of lines and they have a one-to-one relationship. That is, line 62,324 in file1 goes with line 62,324 in file2.

Answer 1

Not sure what operating system you're on, but if you're using Linux, using the paste command is probably a lot easier than trying to do this in PHP.

If this is a viable solution and you don't absolutely need to do it in PHP, you could try the following:

paste -d ',' file1 file2 > combined_file