Writing and editing

Putting text into a file

You can use the cat command to create a file quickly by typing cat > filename. cat creates a file named filename, and puts the text you type into the file, until you tell it you have finished by pressing <Ctrl>D. (The name cat is short for concatenate, or join together; this is another thing the cat command can do.)

   $ cat > todo
   write staff report
   review budget figures
   return doug's call
   <Ctrl>D

Using cat to write a file is like writing a mail message: you can backspace to correct mistakes within a line, but you cannot backspace past the beginning of the line you are on. The vi editor, discussed later in this chapter, lets you correct mistakes anywhere in a file.

Try writing a file with cat:

Type cd; pwd and press <Enter> to make sure you are in your home directory.
Type cat > mytodo and press <Enter> to open up a file called mytodo. Everything you type now goes into mytodo, until you press <Ctrl>D.
Type in the text as shown in the following screen display. Remember to press <Enter> to start each new line.
When you have finished typing the text, go to a new line and press <Ctrl>D.

Type l mytodo and press <Enter> to check that the file was created.

$ cd; pwd
/u/susannah
$ cat > mytodo
write status report
fill out timesheet
buy cat food
<Ctrl>D
$ l mytodo
-rw-rw----   1 susannah techpubs      52 Jun 24 12:12 mytodo

Q: What if I see a message like:
mytodo: Permission denied or
mytodo: cannot create?

A: When you see a Permission denied or cannot create message, this means you do not have permission to write in the directory where cat is trying to create a file. (File and directory permissions are covered in ``Protecting files and directories''.) Try changing to your home directory by typing cd and pressing <Enter>, then try opening up your new file there.