Rename files in a specific way. Target nth string between symbols - powershell

Question

Apologies in advance for a bit vague question (no coding progress).
I have files (they can be .csv but dont have .csv, but that I can add via script easy). The files' name is something like this:
TRD_123456789_ABC123456789_YYMMDD_HHMMSS_12345678_12345_blabla_blabla_blabla_blabla
Now I would need a script that renames the file in a way that it keeps original name except:
It would cut off the ending (blabla_blabla_blabla_blabla) part.
Changes the 12345 before blabla to random 5 characters (can be numbers too)
Change timestamp of HHMMSS to current Hours, minutes, seconds.
In regards to point 3. I think that I can insert arbitary powershell script to any string in " " queotes. So when renaming the files, I was thinking I could just add
Rename-Item -NewName {... + $(get-date -f hhmmss) + ...}
However, I am lost how to write renaming script that renames parts between 4th & 5th _ symbol. And removes string part after 7th _ symbol.
Can somebody help me with the script or help me how to in powershell script target string between Nth Symbols?
Kind Regards,
Kamil.

Answer 1

Split the string on _:
$string = 'TRD_123456789_ABC123456789_YYMMDD_HHMMSS_12345678_12345_blabla_blabla_blabla_blabla'
$parts = $string -split '_'
Then discard all but the first 6 substrings (eg. drop the 12345 part and anything thereafter):
$parts = $parts[0..5]
Now add your random 5-digit number:
$parts = #($parts; '{0:D5}' -f $(Get-Random -Maximum 100000))
Update the string at index 4 (the HHMMSS string):
$parts[4] = Get-Date -Format 'HHmmss'
And finally join all the substrings together with _ again:
$newString = $parts -join '_'
Putting it all together, you could write a nice little helper function:
function Get-NewName {
param(
[string]$Name
)
# split and discard
$parts = $Name -split '_' |Select -First 6
# add random number
$parts = #($parts; '{0:D5}' -f $(Get-Random -Maximum 100000))
# update timestamp
$parts[4] = Get-Date -Format 'HHmmss'
# return new string
return $parts -join '_'
}
And then do:
Get-ChildItem -File -Filter TRD_* |Rename-Item -NewName { Get-NewName $_.Name }