Creating, deleting

• One way to create a file is with the cat command, but in the following strange way: cat $>$ filename. cat is really a multipurpose utility which we will meet again and again, and actually appends one file to another. cat $>$ means append input from the keyboard to the file filename , and is an example of redirection, to be treated a little later. If filename exists, it will overwrite the file. You write, hitting return after each line, and when you are finished, you go to the next line and type Control-d to exit and save.

  For example, (you should create this file in /home/vastro/tutorial/texts.)

  % cat $>$ test.txt
  There was a young woman named Bright
  Whose speed was much faster than light.
  She set out one day
  In a relative way,
  And returned on the previous night.
  Control-d
  %

  $\bullet$ Question 8: How would you view the contents of test.txt to make sure it was saved properly?

• Another way to create a file is to use emacs, which is a very easy to use word processor. We will talk about emacs at some point.

• cp is another way to create a file, by copying one file to another.

  For example,

  % cp test.txt test2.txt
  creates the file test2.txt which is identical to test.txt. This is a useful way to create backup copies of files on which you perform regular, but dramatic changes. That is, if you screw up, you can always go back to the most recent update.

• mv is yet another way to create a file, but you lose the original file. It has two functions, moving files from one directory to another, or to rename files in the same directory. You can also in principle move a file to another directory while changing its name.

  For example, (don't perform this example)

  % mv test.txt trial_texts
  moves test.txt from the current directory to the subdirectory texts. Also,

  % mv test.txt probe.txt
  copies test.txt to probe.txt, and removes the filee test.txt. That is, you've renamed the file from test.txt to probe.txt. Finally,

  % mv test.txt trial_texts/probe.txt
  moves test.text to the directory text, and changes the file name to probe.txt.

• To remove a file, use the command rm filename

  For example,

  % rm test.txt
  removes the file we just created. However, the copy with the different name remains.

• rmdir removes a directory. However, note that the directory must be empty of all files before you can delete it.

  $\bullet$ Question 9: In your own words, what is the purpose of the commands rm, cp, mv and rmdir?

  $\circ$ Exercise 9: List the contents of the current directory. (It should be the directory /home/vastro/tutorial/data.) Notice that one file there has an unusually long name. Use mv to change this name to one analogous to pdiode_3100.dat.

• To create a directory, use the command mkdir directoryname.

  $\circ$ Exercise 10: Go the the directory tutorial and remove the subdirectory ps using the rmdir command. What happens?

  $\circ$ Exercise 11: Copy the file zzz.ps from the directory tutorial to the subdirectory ps and delete the copy in tutorial using rm. Repeat the process, putting zzz.ps back into the directory tutorial. Finally, put the file in ps using mv. Which process was easier?