Develop Reference

I want to enable or say start WiFi tethering in android device by executing adb shell command

I want to enable hotspot or say start WiFi tethering in android device by executing adb shell command.
What is the adb command used for it?
To turn on bluetooth - adb shell am start -a android.bluetooth.adapter.action.REQUEST_ENABLE.
To open wifi- adb shell am start -n com.android.settings/.wifi.WifiSettings.
But I can not find for turning on hotspot.

How to verify that phone is connected to any cellular service provider?

I found how to call , but even when the device has no sim card it returns no error, so it doesn't help me:
adb -s <device number> shell am start -a android.intent.action.CALL -d tel:55678888

You can read the content of telephony.registry by using - adb shell dumpsys telephony.registry and then parse it. Look for the value of mServiceState:
0 - In Service
1 - Out of Service
2 - Emergency Only

adb shell "watch" command to monitor

I am trying to monitor some commands in my adb shell and I could go watch adb shell <command> but the extra time to have to connect up to the shell is killing me.
Does the Android adb shell have its own version of watch so I can monitor some commands

while true; do <command>; sleep 2; done

How to verify WIFI wake lock using adb command

Can someone tell me is there any adb command to verify wifi wake lock in android phone. I am trying to check that wake lock is active or not after acquire from my application but not found this information in following file:
adb shell "cat /sys/kernel/debug/wakeup_sources"
Is it written somewhere else ?

To list the wifilocks active in android device, use the following command.
adb shell dumpsys wifi | grep "your wake_lock tag name"
Example:
adb shell dumpsys wifi | grep wake_lock_next
output:
WifiLock{wake_lock_next type=2 binder=android.os.BinderProxy#420bcfd0}

How to test wifi connection via adb?

Im automating wifi off/on via adb.
I would either like to disable/enable wifi based on the test case
so far I have found good information here
However I want to test the connection before executing following command
adb shell am start -a android.intent.action.MAIN -n com.android.settings/.wifi.WifiSettings adb shell input keyevent 19 & adb shell input keyevent 19 & adb shell input keyevent 23
Above command disables wifi if enabled, enables wifi if disabled. I want to first test the connection and take action if required. I am wondering if there is a way to do using adb command. This can be achieved programatically but I want it to be done through adb for making it more reliable.
Also following command works only if device is rooted
adb shell "svc wifi enable"
Also following command launches test on screen but provides no info via adb
adb shell am start -n com.android.settings/.wifi.WifiStatusTest

To know everything about Wifi status of the device:
adb shell dumpsys wifi
To just know whether it's enabled or not:
adb shell dumpsys wifi | grep "Wi-Fi is"
To know more detailed status:
adb shell dumpsys wifi | grep "mNetworkInfo"
If connected to a valid network, it shows
"CONNECTED/CONNECTED". It also shows the name of the connected network.
If wifi has been enabled but it is yet to connect to a network, it shows "DISCONNECTED/SCANNING".
If wifi is disabled, it shows "DISCONNECTED/DISCONNECTED".

Below command will give you the internet status and connectivity mode(cellular or Wi-Fi)
adb shell dumpsys connectivity

If you're trying to determine whether or not WiFi is turned on you can run adb shell settings get global wifi_on which returns 1 if it's on and 0 if it's off.
If you have multiple devices connected you can run adb -s [UDID_HERE] shell settings get global wifi_on to get the WiFi status of an individual phone. To find the UDID you can run adb devices.

This would only tell you if there is internet access but you can do:
adb shell ping www.google.com

adb shell dumpsys wifi | sed -n '1p'
is faster and safer than
adb shell dumpsys wifi | grep "Wi-Fi is"
because the output of dumpsys wifi contains the system logs that may have been contaminated by other applications

Atish's answer was working fine until Android 11/R. For this OS onwards, I recommend using Abhishek's suggestion:
adb shell dumpsys wifi | grep "curState=ConnectedState"

Not perfect, but you could dump UI layout and then search for ON/OFF text like this (bash):
adb pull $(adb shell uiautomator dump | grep -o '[^ ]*.xml') ui.xml
grep 'text="OFF"' ui.xml
if [ $? == 0 ]; then
# Turn WIFI on
fi