Using bash to copy IPTC data

[Dotan Cohen]

I have a bunch of pictures that I need to copy IPTC data from one
field to another. I understand that the exiftool utility can do this
and I installed it, but I cannot get it to do what I need (I'm no
computer guru). I need the IPTC feild #118 ( $iptc["2#118"][0] in PHP
) to be copied to the IPTC feild #025 ( $iptc["2#025"][0] in PHP ).
What bash command would do that on hundreds of photos in a recursive
directory structure? I've no bash experience but I know enough php to
look at it and understand it, if it is possible to use the tool via
PHP. Thanks in advance.

Dotan Cohen
http://ie-only.com