Chapter 2: Basic File Operations

cp (copy)

cp file1 file2 is the command which makes a copy of file1 in the current working directory and calls it file2.

What we are going to do now, is to take a file stored in an open access area of the file system, and use the cp command to copy it to your linuxstuff directory.

First, cd to your linuxstuff directory:

Then at the bash prompt, type,

(Note: Don't forget the dot (.) at the end. Remember, in Linux, the dot means the current directory.) The above command means copy the file science.txt to the current directory, keeping the name the same. (Note: The directory /apps is an area where supercomputing applications are stored and every user has read access to this area.)

mv (move)

mv file1 file2 moves (or renames) file1 to file2. This has the effect of moving rather than copying the file, so you end up with only one file rather than two. It can also be used to rename a file, by moving the file to the same directory, but giving it a different name.

We are now going to move the file science.bak to your backup directory. First, change directories to your linuxstuff directory (can you remember how?). Then, inside the linuxstuff directory, type

Type ls and ls backups to see if it has worked.

rm (remove), rmdir (remove directory)

To delete (remove) a file, use the rm command. As an example, we are going to create a copy of the science.txt file then delete it.

Inside your linuxstuff directory, type

You can use the rmdir command to remove a directory (make sure it is empty first). Try to remove the backups directory. You will not be able to since rmdir will not let you remove a non-empty directory. If you wish to remove a directory and its contents use the rm -r command, but be careful and make sure this is exactly what you want!

clear (clear screen)

Before you start the next section, you may like to clear the terminal window of the previous commands so the output of the following commands can be clearly understood.

At the prompt, type

This will clear all text and leave you with the $ prompt at the top of the window.

cat (concatenate)

The command cat can be used to display the contents of a file on the screen. Type:

As you can see, the file is longer than than the size of the window, so it scrolls past making it unreadable.

less

The command less writes the contents of a file onto the screen a page at a time. Type

Press the [spacebar] if you want to see another page, type [Q] if you want to quit reading. You can also use the arrow keys and page up/down keys to scroll through the file as you would in a text editor. As you can see, less is used in preference to cat for long files.

head

The head command writes the first ten lines of a file to the screen.

First, clear the screen, then type

Then type

What difference did the -5 do to the head command?

tail

The tail command writes the last ten lines of a file to the screen.

Clear the screen and type

How can you view the last 15 lines of the file?

Simple searching using less

Using less, you can search though a text file for a keyword (pattern). For example, to search through science.txt for the word 'science', type

then, still in less (i.e. don't press [q] to quit), type a forward slash [/] followed by the word to search

As you can see, less finds and highlights the keyword. Type [N] to search for the next occurrence of the word. You can also hold down [Shift] and type [N] to search for the previous occurrence of the word.

grep

grep is one of many standard Linux utilities. It searches files for specified words or patterns. First clear the screen, then type

As you can see, grep has printed out each line containg the word science, or has it?

Try typing

The grep command is case sensitive by default; it distinguishes between Science and science. To ignore upper/lower case distinctions, use the -i option, i.e. type

To search for a phrase or pattern, you must enclose it in single quotes (the apostrophe symbol). For example to search for spinning top, type

Some of the other options of grep are:

• -v display those lines that do NOT match
• -n precede each matching line with the line number
• -c print only the total count of matched lines

Try some of them and see the different results. Don't forget that you can use more than one option at a time, for example, the number of lines without the words science or Science is

wc (word count)

A handy little utility is the wc command, short for word count. To do a word count on science.txt, type

To find out how many lines the file has, type