7. Write a complete command that will look for any digit 0-9 and replace it with the corresponding letter A-J in file "test.txt". For example, "zero is 0 one is 1 two is 2" would come out "zero is A one is B two is C". You can create such a "test.txt" file by yourself for testing purpose. 8. You have a shell variable named LOGNAME that contains your login name. I want one command line that will set the shell variable GNUM to the group ID for you listed in the password file. Please do not directly use your login name in the command like "grep 'ruizhao' /etc/passwd", please use the LOGNAME. Hint: What is the format of /etc/passwd file? How to use a variable's value in command? How to use regular expression to find your login name in such a file? Or you may have a smarter way