I would like to copy the value in the [IPTC]Source tag to the [XMP]Source tag in the same file.
I have tried:
exiftool "-iptc:source<xmp:source" [file]
however it doesn't seem to work. What would be the correct way to structure the command?
In what way doesn't it work? What is the exact output from exiftool when running that command? Are you checking for the change with exiftool (use the command in FAQ #3 (https://exiftool.org/faq.html#Q3)) or with some other program?
That is the correct command and it works correctly here
C:\>exiftool -G1 -a -s -source y:\!temp\Test4.jpg
[IPTC] Source : test
[XMP-photoshop] Source : NewTest
C:\>exiftool -G1 -a -s "-iptc:source<xmp:source" y:\!temp\Test4.jpg
1 image files updated
C:\>exiftool -G1 -a -s -source y:\!temp\Test4.jpg
[IPTC] Source : NewTest
[XMP-photoshop] Source : NewTest