syntax error when running iperf through adb

Question

I am trying to execute iperf through adb shell, however I am getting following error:

syntax error: unexpected 'newline'

here are the steps:

1. push android compiled iperf binary to /data/local/tmp

2. enter adb shell, go to /data/local/tmp folder.

3. chmod +x ./iperf2.0.10

4. ./iperf2.0.10

5. I tried executing command from outside like: adb shell "command"

6. I tried few other phones.

7. I tried few iperf versions.

host machine: tried both mac and windows. on windows version info:

Android Debug Bridge version 1.0.41
Version 31.0.3-7562133

phone info: adb shell getprop ro.product.cpu.abilist
arm64-v8a,armeabi-v7a,armeabi

I made sure to pick relevant iperf binary form: https://github.com/KnightWhoSayNi/android-iperf

This is a galaxy S7 SM-G930U, android version 8.0.0, kernel version 3.18.71-14970140

I looked at the iperf source code and could not find any place which would print this error message, so seems like some issue with how adb is treating my command.

Please suggest what can I do now ?

Edit: updated some details