Text files

In Linux files that are human readable are often referred to as text files, and files that are machine readable are referred to as binary files. All programs are binary files and so programs are often referred to as binaries.

If you want to look at the contents of a text file there are several commands you might want to use.

• cat
  Short for `concatenate' this command writes a file or files to the terminal window.
• head
  Writes the first few ten lines of the file to the terminal window. You can use head -24 to write the first 24 lines, or use any number you like.
• tail
  This is like head but writes the last few lines of a file to a terminal. A particularly useful switch is `-f' which writes the end of the file and then waits for any changes to the file and writes those as they are written. To quit, hold down the control key and press X (more about the control key later).
• more and less
  The more command, and the slightly more advanced less, let you look at a file interactively. The display the first window full of text from the file, and then you can press the spacebar to scroll down by one page or the b key to scroll back up one page. You can also search for text by typing `/' followed by the text you wish to search for, and then pressing the enter key. To go to the next occurence of the text press `n' and `b' will take you back to the previous occurence. The less command will also let you move through the file using the arrow keys. Press `q' to quit.
• grep
  This is an extremely useful command which is used to search a file or files for a particular text string or pattern. We will return to this command later.

One common task we use computers for is to create or edit text files. There are many text editors available under Linux, but probably the most common are vi, emacs and pico.

Please note that these are text editors, not word processors or typesetting programs - they don't have any founts or different sizes of text, and the output will not look pretty. However they are quick to load, reasonably quick to run over a network, and will not insert any nasty command characters into your document.