There is a conditional branch instruction in sed that is taken if the last substitute command was successful. The O'Reilly book on sed & awk is available onlin

There is a conditional branch instruction in sed that is taken if the last substitute command was successful. The O'Reilly book on sed & awk is available online for free from various sources (I grabbed a rar archive of it from somewhere). https://freecomputerbooks.com/The-Unix-CD-Bookshelf-Version-2-1.html https://freecomputerbooks.com/The-Unix-CD-Bookshelf-Version-...