Append Filename Into Keyword Tag - ANSWERED

[RossGoodman]

Phew - what an extensive tool but I'm struggling with the basics !
I want to append the filename into the tag attribute (what PhotoShop/Picasa/Windows Explorer) calls a photo tag.
Through trial and error I have worked out that this is the keyword tag and have managed to get the following to run:

exiftool.exe "-keywords<${filename}" *.*

However what I would actually like to do is append the filename just in case there are any existing tags.
I tried

exiftool.exe "-keywords+=${filename}" *.*

but that put the literal ${filename} in.

Many thanks in advance

[StarGeek]

You're close.  The Equal Sign is used to assign a static value to a tag.  The Greater/Less Than Signs are used to copy one tag to another. 

Try
exiftool.exe "-keywords+<filename" *

You don't need to use the ${filename} format when you are just copying a tag.  You would want to use it if you were to alter the tag name in some way, either through the use of Advanced Formatting, adding another tag in the same line, or adding some other text.  Another use would be using the NoDups option just in case you already added the filename before and forgot and wanted to avoid duplicate keywords:
exiftool.exe "-keywords+<${filename;NoDups}" *

[RossGoodman]

Perfect - works a treat.

Amazed at the prompt response!