The intention of this article is to assist you in identifying the Routing Engine that you are currently logged into. 

Option 1 : The practice of adding Routing Engine (RE) information to hostnames can be quite beneficial in identifying the routing engine that we are currently logged into. 

{master}
labroot@labrouter-RE0> show chassis hardware | match routing 
Routing Engine 0 REV 11   740-041821   90XXXXXX26        RE-S-1800x4
Routing Engine 1 REV 12   740-041821   90XXXXXX04        RE-S-1800x4

{master}
labroot@labrouter-RE0> show configuration groups re0 |display set 
set groups re0 system host-name labrouter-RE0

{master}
labroot@labrouter-RE0> show configuration groups re1 |display set    
set groups re1 system host-name labrouter-RE1

{master}
labroot@labrouter-RE0> show configuration apply-groups |display set 
set apply-groups re0
set apply-groups re1

{master}
labroot@labrouter-RE0> request routing-engine login other-routing-engine 
Last login: Mon Dec 30 04:28:38 from re0

--- JUNOS 21.2R3-S7.7 Kernel 64-bit  JNPR-12.1-20231013.2183cac_buil
...

{backup}
labroot@labrouter-RE1> 

Option 2 : Running the command below can help identify the routing engine you are currently logged into

{master}
labroot@labrouter-RE0> start shell command "sysctl -a kern.junos_hostname" 
kern.junos_hostname: re0

{master}
labroot@labrouter-RE0> request routing-engine login other-routing-engine 

{backup}
labroot@labrouter-RE1> start shell command "sysctl -a kern.junos_hostname" 
kern.junos_hostname: re1