Iperf3 - Put hour/minutes/seconds at the beginning of each line

I'm currently trying to launch a very long Iperf test on my infrastructure, so I'm developing some powershell script in order to do the tests.

To analyses the results, I want to have the hour/minutes/seconds of each new packet sends per lines on my output.

Currently, I'm using the -T argument like that on my script :

Start-Process -FilePath "C:\iperf3.exe" -Verb runAs -ArgumentList "-c",CLIENT_IP,"-t","86400","-p",5102,"-T","$(Get-Date -Format 'HH:mm:ss')","--logfile","C:\toto.txt"

But the output of the command just give me the current time when I launch the command like this:

03:40:56:  Connecting to host x.x.x.x, port 5201
03:40:56:  [  4] local x.x.x.x port 41674 connected to x.x.x.x port 5201
03:40:56:  [ ID] Interval           Transfer     Bandwidth       Retr  Cwnd
03:40:56:  [  4]   0.00-1.00   sec   113 MBytes   946 Mbits/sec    0    208 KBytes       
03:40:56:  [  4]   1.00-2.00   sec   112 MBytes   943 Mbits/sec    0    208 KBytes       
03:40:56:  [  4]   2.00-3.00   sec   112 MBytes   939 Mbits/sec    0    210 KBytes       
03:40:56:  [  4]   3.00-4.00   sec   112 MBytes   942 Mbits/sec    0    210 KBytes       
03:40:56:  [  4]   4.00-5.00   sec   112 MBytes   940 Mbits/sec    0    210 KBytes

And I cannot find a way to increment the value with the current time without relaunching several times the command iperf3.exe.

Is there any solution to increment the value? I can't do it with a "for"/"while" loop (in my opinion) because it's running a lot of iperf3 instance and it's not what is expected.

For information, I use the last version of iperf3-3.1.3 on Windows.

Thanks in advance for your help.

Solution

Judging by iperf3's documentation:

-T (--title) is for defining a static prefix to prepend to each output line, due to passing expandable string "$(Get-Date -Format 'HH:mm:ss')" as an argument, a static string representing the time at the time of string expansion (interpolation) is used.
By contrast, what you're looking for is the --timestamps option, which causes a (true, event-related) timestamp to be prepended to each output line.
- You can control the specific format of these timestamps via an optional argument, using a format string as used in the Unix strftime() library function.
- These format strings are not compatible with .NET's date/time format strings (as used by Get-Date, for instance), so HH:mm:ss does not work; the strftime() equivalent is: %H:%M:%S

To put it all together:

Start-Process -FilePath 'C:\iperf3.exe' -Verb RunAs -ArgumentList @"
 -c $client_IP -t 86400 -p 5102 --logfile C:\toto.txt --timestamps=%H:%M:%S
"@

^{Note: I've substituted CLIENT_IP (which I assume was just a pseudo-code placeholder), with variable $client_IP - adjust as needed.}