IF
If condition evaluates to TRUE, then execute all commands in cmdlist,
else execute all commands in cmdlist2.
IF condition THEN command
IF condition THEN { cmdlist }
IF condition THEN command1 ELSE command2
IF condition THEN { cmdlist } ELSE command2
IF condition THEN command1 ELSE { cmdlist2 }
IF condition THEN { cmdlist } ELSE { cmdlist2 }