Question on the NiFi processor UpdateAttribute

[E M]

In the processor there is a field for Delete Attributes Expression which
supports Regular Expression patterns.

I'm trying to use a negative look ahead in order to get rid of a lot of
attributes.
Rather than to try and type out 50+ other attributes I don't want I want to
use negative lookahead in order to just drop things that are not of the
format I want to keep.

Does this processor or any NiFi processor support negative lookahead
regular expression patterns?


-- 
Respectfully,
Elijah
edjm1...@gmail.com

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Looking for clarity on using NiFi

[E M]

https://nifi.apache.org/docs/nifi-docs/components/org.apache.nifi/nifi-standard-nar/1.6.0/org.apache.nifi.processors.standard.EnforceOrder/

Fairly new with NiFi, looking for information that is just lacking.
I'm trying to do what I consider to be a very basic feat.
Get a bunch of files.
Sort those files by their name or whatever I want.
I found the documentation but it is just lacking.
For examples,
The documentation states to on the 'Initial Order'
When the first FlowFile of a group arrives, initial target order will be
computed and stored in the managed state. After that, target order will
start being tracked by EnforceOrder and stored in the state management
store. If Expression Language is used but evaluated result was not an
integer, then the FlowFile will be routed to failure, and initial order
will be left unknown until consecutive FlowFiles provide a valid initial
order.
*Supports Expression Language: true (will be evaluated using flow file
attributes and variable registry)*
and
The documentation states to on the 'Order Attribute'
A name of FlowFile attribute whose value will be used to enforce order of
FlowFiles within a group. If a FlowFile does not have this attribute, or
its value is not an integer, the FlowFile will be routed to failure.

Neither of these clearly present me with how to use this software.
It probably means more to someone who already knew how to do it and it just
is a reminder to them but for new people we are left scratching our heads.

I've been Googling for 3 hours trying to find an answer.
Can you clarify?


-- 
Respectfully,
Elijah