[pbohun]

Was it joining on some columns or just concatenating the files?

I'm going to laugh pretty hard if it could just be done with: cat file1.csv file2.csv > combined.csv

[xnx]

There are also a lot of command line options for joining by column like csvkit

[Xenoamorphous]

You need to account for the headers, which many (most?) csv files I've encountered have.

So I guess something like this to skip the headers in the second file (this also assumes that headers don't have line breaks):

  cp file1.csv combined.csv && tail -n+2 file2.csv >> combined.csv