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Warning - It's Goodbye, not Au Revoir

Unix assumes you know what you are doing. For example, if you remove a file, the file will be removed. It won't be placed in the trash, and you won't be asked for confirmation. The file will be removed just as you ordered. The file will never been seen again. Goodbye. (This assumes you have the necessary permissions to delete the file.)

If you copy file-one to file-two, and file-two already exists, the copy of file-one will overwrite the old file-two. Gone. Well, why not? You did know what you were doing. You did know that file-two already existed. Didn't you?

The same goes for moving. Moving file-one to file-two will overwrite any existing file-two. The old file-two will be gone.

If this behaviour makes you a little nervous, the option '-i' may help calm you.

Create two files with:

% touch x y

Now, try to rename 'x' to 'y', with and without option '-i'

% mv -i x y
% mv x y

The first version will prompt you asking if you really want to overwrite y. The second won't. (The second will fail if you have allowed the first to move x.)

And again for copy:

% touch x y
% cp -i x y
% cp x y

Again, the first version will prompt for confirmation.

And for a safe removal:

% rm -i x y

In all the above examples, option '-i' specifies interactive mode.

Viewing Files

How does one examine a file? Using a text editor such as 'pico', 'emacs', or 'vi' is one option. Listing to the Terminal window is a second. I will cover text editors in a later tutorial, and concentrate on the latter option now.

Firstly, create 'file-one' and display it.

The simplest command is 'cat' which lists the contents of a file to the Terminal window:

% man tcsh > file-one
% cat file-one

The file will whiz by, scrolling out of the window.

You can view the file by pressing page up and page down (the keys below F15). Select 'Control' from the Terminal menu to see other keys for moving around. Here we are making use of the Terminal's scroll-back buffer. A more elegant method is to use a better viewer.

View More

% more file-one

Will display the first screen-full of 'file-one'. On the bottom line is some inverse text giving the file name and percentage of the file displayed so far. 'more' understands many single-key commands to browse the file.

return to display the next line
'd' to display the next half-screen
space bar to display the next screen-full
'q' to quit 'more'

'more' does more than I have described, but let's concentrate on 'less', which actually does more than 'more'.

View Less

At this point it's obligatory to say 'less is more'. 'less' allows one to scroll back and forth through a file, as well as providing a nicer search facility.

% less file-one

Try the following keys:

return spacebar
'u' 'd'
up-arrow down-arrow
control-g
and 'q' to quit 'less'

To search for some text within the file, for example 'history', type:

/history (return)

and hit 'n' to search for the next occurrence. Notice how each occurrence of 'history' is highlighted. This will remain so as you view more of the file.

?history

will search backwards, with 'n' continuing the backward direction.

Finally, hit 'q' to quit.

'less' does so much more than I have described above. As ever:

% man less

A Unix Trash

If you wish to use the Finder's trash when deleting files you can simply move them to the trash using 'mv'.

% mv file ~/.Trash/

The (hidden) trash directory is in your home directory, and is called '.Trash'

'file' will be deleted when the trash is emptied in the normal manner.

Home Grown Trasher

Issue this command (all on one line):

% alias trash mv \!\* ~/.Trash/

Now, use your new trash command:

% touch xxx
% trash xxx

and look in the trash using Unix or the Finder.

'alias' is a form of text substitution. When you type 'trash' on the command line it will be substituted with

mv parameters ~/.Trash

where 'parameters' is whatever you typed after 'trash'. I will not explain aliases in depth until a later tutorial.

Note

Make sure you never accidentally create a file called '.Trash'. It must always be a directory.

Cat and Mouse

'cat' is not a Unix command to scare the mouse. It is short for concatenate and will join two or more files, writing the results to the Terminal.

% cat file-one file-two

'man' to 'more'

The 'man' command displays its output using 'more'. So all the commands that work with 'more' can be applied to 'man'.

I prefer 'man' to use 'less' instead. This can be achieved in two ways.

As a temporary solution:

% man tcsh | less

To make 'less' the default viewer for the duration of the Terminal session:

% setenv PAGER less

Now use the key-strokes you would for 'less'.

'setenv' is a command that affects your environment, in this case by setting 'PAGER' to 'less'. 'man' looks at 'PAGER' to see if a different viewer has been specified.

vi

If you are familiar with the 'vi' editor, you will already know most of the commands that 'less' will accept. There is much common ground between the two, and in fact many other Unix tools too.