I need to rename a file but keep part of the existing name.
Current name: Test1_20080812.txt
New name must be: ABTestFile_<same date as current filename>.txt

The file can get created on a different date to when the file must be renamed, so I can not make use of a date varibale and I am not having luck with a working file mask.
Thanks.

Is the first part of name "Test1" of a fixed length?

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Yes it is a fixed length.

You could use the substring method like this:

ABTestFile{STRING(Substring|Test1_20080812.txt|6|12)}

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The problem is that original file name value is not static. So the date componetn of the file name (20080812) changes for every name.
Is there any way that I can specifiy the original file name in the substring i.e.
ABTestFile{STRING(Substring|{original file name here}|6|12)}