Followup on Practice 1

Logging in, File system Basics, Editing Basics

Here are answers for the lab questions.

1. What is the absolute pathname of your home directory?
   
   To find out your absolute pathname, change to your home directory and then ask for the name of the directory as follows:
   

   -> cd
   -> pwd
   

   The absolute pathname should begin with /home/cs-students/. Following this should be your login id.
   

2. Use xman to find some interesting commands. For example,

• Find a command that displays a clock on your screen. (Then display a clock.)
  
  To find a clock program, open a manual page with xman. Then use the search command from the Options menu. Type clock and then click the Apropos button. Remember that you only need to look at enties in Section 1 in the manual, denoted by (1). You should find three different clock programs: clock, oclock, and xclock. To start any of these go to your shell window and type
  

  -> oclock &

  
  This will create a new window displaying an oval clock. If you forget the & at the end of the command, you will no longer be able to use the shell. See Lecture Notes 2 for information on what to do in that case.

• Find a command to compare two text files showing you the lines that differ. Use it to compare the file you are creating with its backup file.
  
  This one is a bit trickier. Again, use xman. You might try using "compare" as the keyword to search on. Among othere things, this will list cmp as a likely command to use. When you read the man page, though, you will see that cmp only prints out the location of the first difference. It doesn't show you the differences. This command is useful if you just want to know if two files have the same contents. If you scroll to the bottom of the man page, you will see some related commands. With some investigation, you should discover that diff is the right command for this purpose. Why doesn't diff come up in the initial search? Simply, because it does not have the word "compare" in its one line description. If you happened to use "differ" in your keyword search, you should have found diff more quickly.
  
• Find a command that will search through all your files looking for files that match certain criteria (like Sherlock on the Mac). Use it to find all your files that have not been modified in the last 24 hours. (Warning: This may be tricky to figure out.)
  
  If you use "find" as the keyword to search for, you should discover the find command pretty quickly. The difficult part in this case is understanding the man page so that you can use the command to get the desired effect. Here is the proper command line:
  

  find ! -mtime 1

  
  The -mtime flag finds files that have been modified in the last n days. In this case we use 1 for the n argument. Now, we want to know those that have not been modified so we precede the -mtime argument with the not operator, which is ! (as in C).
  

1. Create a directory. Copy one of your files into the directory. Now remove the directory. What commands did you need to do to accomplish all of these.
   
   There are a variety of ways of accomplishing this, but your first attempts will probably not succeed. If you type "rm <dirname>", you will be told that the directory is not empty and the remove command fails. If you look at the rm man page, you should find the -r argument. rm -r <dirname> will do the trick. You need to be very careful about the use of this command as you may potentially delete a lot of files. It is always best to do an "ls -a -R" command before an "rm" command using the same arguments so that you can see exactly what will be deleted. -a includes files whose names begin with . and -R recursively lists the contents of directories.
   
2. Use Emacs info to find a command that will spell check the file you are creating. Now, run the spellchecker.
   
   Using info you should find the entry for ispell. If you look at the info for ispell, you should find the command ispell-buffer. You run ispell-buffer by typing M-x ispell-buffer. (Remember that M- means that you should use the Escape key. Also remember that Escape is a separate keystroke from the following character, not chorded like the control character is.) A prompt at the bottom of the screen will you give you more information on how to use the command. Basically, it walks through your buffer from the top, highlighting potentially misspelled words. Hitting the space bar will move on to the next word without changing the current word. r will allow you to type in an arbitrary replacement for the word. If the spell checker has somre reasonable alternatives, they will be shown at the top of the window preceded by a number. If you type in a number that correction will be applied.