Exercises

The UNIX shell is case-sensitive, meaning that an uppercase letter is not equivalent to the same lower case letter (i.e., "A" is not equal to "a"). Most all unix commands are lower case.

1. Finding out which shell you are using. Use the SHELL environment variable.
2. Displaying current variables. Say, to display the value of PATH environment variable.
3. Changing to your home directory.
4. Changing default access permissions. Use umask, first start with man umask.
5. Changing access permissions. Change the access permissions of a file or directory.
6. Analyse of using pipelines (to connect commands);

    $who | wc -l
    $ps aux | grep ozdogan |sort +5 -6|more
    $cat file | head -75 | tail -50
    $grep 'your username' /etc/passwd
   

7. What is the relative pathname?
8. To change your password, type the command , using the passwd utility. Here are some rules for selecting a good password:
   • Do not use any part of your name, your spouse's name, your child's name, your pet's name, or anybody's name. Do not use any backward spellings of any name, either.
   • Do not use an easily-guessable number, like your phone number, your social security number, your address, license plate number, etc.
   • Do not use any word that can be found in an English or foreign-language dictionary.
   • Do not use all the same letter, or a simple sequence of keys on the keyboard, like qwerty.
   • Do use a mix of upper-case and lower-case letters, numbers, and control characters.
   • Do use at least six characters.
9. When you execute a non built-in shell command, the shell asks the kernel to create a new subprocess (called a "child" process) to perform the command. The child process exists just long enough to execute the command. The shell waits until the child process finishes before it will accept the next command. Explain why the exit (logout) procedure must be built in to the shell.