Week 6 Tutorial Exercises

1. What will be matched by the following regular expressions?
   1. x*
   2. xx*
   3. [0-9]
   4. [0-9]*
   5. [0-9][0-9][0-9]
   6. ^\...
   7. [A-Za-z_][a-zA-Z_0-9]*
   8. ^Begin$
   9. ^\(.\).*\1$
2. What will be the effect of the following commands?
   1. who | grep 'mary'
   2. who | grep '^mary'
   3. grep '[Uu]nix' ch?/*
   4. date | cut -c 12-16
3. Write the commands to:
   1. Find all logged in users with user names of at least 6 characters
   2. Find all users on your system whose user ids are greater than 99 (Hint: user ids are the third field in the file /etc/passwd)
   3. Find the number of users on your system whose user ids are greater than 99
4. What will be the effect of the following command

   
       sed 's/\([Uu]nix\)/\1(TM)/g' text > text.out
     

   if the file text contains the line
   "The Unix operating system was pioneered by Ken Thompson"