Now, I finally can send SMS through the command line on an Android 8.0-oreo performing next steps:

• Installing the ShellMS app on the phone (once for ever)
• Going on the phone to Settings > Apps > ShellMS > Permissions > Enable all the permissions (once for ever)
• Connecting the phone to the computer with USB
• Issuing next script on the computer:

#!/bin/bash
phonenumber="$1"
message="$2"
# escape double quotes
message=${message//\"/\\\"} 
adb shell "am startservice --user 0 -n com.android.shellms/.sendSMS -e \"contact\" $phonenumber -e msg \"$message\""

Now, I finally can send SMS through the command line on an Android 8.0-oreo performing next steps:

• Installing the ShellMS app on the phone (once for ever)
• Going on the phone to Settings > Apps > ShellMS > Permissions > Enable all the permissions (once for ever). This step will no longer be necessary once an issue about permissions will be fixed
• Connecting the phone to the computer with USB (and giving permission on the phone for accessing data, if asked)
• Issuing next script on the computer:

#!/bin/bash
phonenumber="$1"
message="$2"
# escape double quotes
message=${message//\"/\\\"} 
adb shell "am startservice --user 0 -n com.android.shellms/.sendSMS -e contact \"$phonenumber\" -e msg \"$message\""