How to detect the physical connected state of a network cable/connector?

Question

In a Linux environment, I need to detect the physical connected or disconnected state of an RJ45 connector to its socket. Preferably using BASH scripting only.

The

Answer 1

Somehow if you want to check if the ethernet cable plugged in linux after the commend:" ifconfig eth0 down". I find a solution: use the ethtool tool.

#ethtool -t eth0
The test result is PASS
The test extra info:
Register test  (offline)         0
Eeprom test    (offline)         0
Interrupt test (offline)         0
Loopback test  (offline)         0
Link test   (on/offline)         0

if cable is connected,link test is 0,otherwise is 1.