Note that /Master_Log_File:\s*(\S*)\s*$/ will match Relay_Master_Log_File and do the right thing because of the order of SHOW SLAVE STATUS (just like Master_Log_Pos), but I still feel it should be changed for clarity.
Note that /Master_ Log_File: \s*(\S* )\s*$/ will match Relay_Master_ Log_File and do the right thing because of the order of SHOW SLAVE STATUS (just like Master_Log_Pos), but I still feel it should be changed for clarity.