Question about function set_dont_touch_network
This command is used to prevent a clock network from being modified or replaced during optimization. It is Design Compiler command which is used during RTL synthesis. 

set_dont_touch_network [get_ports scan_enable*]


it tells the DC to get all scan_enable* ports and also all the cells &amp; nets that are also connected with these ports and then set dont_touch attribute on them. This attribute prevents those cells &amp; ports from being modified during optimization. This is useful when you have an optimized network and you don't want the tool to modify the network during optimization.

There is another command set_dont_touch which sets dont_touch attribute only to the cells, ports &amp; pins specified, not the elements connected in the fanout of them.

the asterisk (*) is actually one of the wild-cards used in various shell environments. it means to match any string or characters. like scan_enable_001, scan_enable_002 etc. Here are more wild-cards used in TCL shell.