Powershell appending files

Hi all i have a script that i will be running several times and combining into a single file.
Is there a way to append only new entries into the file as currently its adding all entries which essentially become duplictaes

thanks
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cwstad2Asked:
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Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
No. A file is no database, and so you do not have anything generic allowing to only append "new" rows. You'll have to filter the newly generated text pre appending, or apply a "sort unique" on the result file after appending data, or doing similar things needing some specific treatment and effort.

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aikimarkCommented:
It depends on what type of data/objects you are dealing with.  Normally, I would say to bring the keys of your target collection into a hash table and then check to see whether new item keys already exist in the hash table before adding/appending.
cwstad2Author Commented:
Hi Aikimark, how would that be possible

thanks
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aikimarkCommented:
1. You create a hash-table (dictionary) variable with @{}
Example:
$d = @{}

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2. You iterate your objects, adding new key:value pairs to the $d variable.
3. When considering new objects for inclusion/addition, you check to see if that new object's key is already in $d
Qlemo"Batchelor", Developer and EE Topic AdvisorCommented:
As said, that requires that you can isolate an unique key element to determine if each entry is new or not. You need to have knowledge about the meaning and layout of the output. E.g. if you want to have a scan over PCs for reachability, and only need to know whether they have been reachable at least once out of n tests, that would make up a list (PC, reachable, last fail or first success time stamp), where you change existing records (or not) and add non-exisiting ones.
cwstad2Author Commented:
Thought it was worth a try

Thanks
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