if it suits your needs, you can simply do this on the commandline with join as well: 
[davidrw@host davidrw]$ join -t , -1 1 -2 4 /tmp/f1 /tmp/f2
upc,qty,product_sku,size,color
840197083284,2,121,LG,Black
840197083291,3,121,XL,Black
840197083307,21,121,2XL,Black

[download]
see "man join" for the various options to get the output the way you need it (espically if you want to show unmatched lines)

In reply to Re: Joining two files on common field by davidrw
in thread Joining two files on common field by ch1

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