How can several pages be simplified if they have the same sentence?

For example, several pages have the following sentence this has a way to simplify it?

if(isset($_COOKIE['isLogin'])){  echo ''.$_COOKIE['username'].''.''.'退出'.'';}

Reply content:

For example, several pages have the following sentence this has a way to simplify it?

if(isset($_COOKIE['isLogin'])){  echo ''.$_COOKIE['username'].''.''.'退出'.'';}

Add to the public include file. If each file is used, it is written directly in the public include file header, if only partially used to encapsulate a function, called where needed.

Written in a public file, you can use it directly require in.
or encapsulated in a function, called directly.

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