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Unix files system

Copying Files

cp (copy)

cp stands for copy. This command is used to copy files or group of files or directory. It creates an exact image of a file on a disk with different file name. cp command require at least two filenames in its arguments. The cp do copy of file1 file2 is the command which makes a copy of file1 in the current working directory and calls it file2

$ cp [OPTION] Source Destination
$ cp [OPTION] Source Directory

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 unixstuff directory.

First, cd to your unixstuff directory.

$ cd ~/unixstuff

Then at the UNIX prompt, type,

$ cp /vol/examples/tutorial/science.txt .

Note: Don’t forget the dot (.) at the end. Remember, in UNIX, 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 /vol/examples/tutorial/ is an area to which everyone in the department has read and copy access. If you are from outside the University, you can grab a copy of the file here. Use ‘File/Save As..’ from the menu bar to save it into your unixstuff directory.

:loudspeaker: Exercise

Create a backup of your science.txt file by copying it to a file called science.bak

Moving files

mv (move)

mv file1 file2 moves (or renames) file1 to file2

To move a file from one place to another, use the mv command. 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 unixstuff directory (can you remember how?). Then, inside the unixstuff directory, type

$ mv science.bak backups/.

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

Removing files and directories

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 unixstuff directory, type

$ cp science.txt tempfile.txt  
$ ls (to check if it has created the file)  
$ rm tempfile.txt  
$ ls (to check if it has deleted the file)

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 UNIX will not let you remove a non-empty directory.

To permanently remove directory use either the rmdir or rm commands:

rmdir unixstuff or 
rm -d unixstuff

The remove commands for various options

Command and Option Description
rm -d Remove an empty directory using the rm command.
rm -r Remove a non-empty directory and its content.
rm -f Ignore any prompt when deleting a write-protected file.
rm -rf Ignore any prompt when deleting a write-protected non-empty folder.
rm -i Output a prompt before deleting every file.
rm -I Output a prompt only once before deleting more than three files.
rm * Wildcard that represents multiple characters.
rm ? Wildcard that represents a single character.
rmdir -p Remove an empty subdirectory and its parent directory.
rmdir -v Print the information that the specified directory was deleted.

:loudspeaker: Exercise

Create a directory called tempstuff using mkdir , then remove it using the rmdir command.

Displaying the contents of a file on the screen

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

$ clear

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:

$ cat science.txt

As you can see, the file is longer 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

$ less science.txt

Press the space-bar if you want to see another page, type q if you want to quit reading. As you can see, less is used in preference to cat for long files.

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

First clear the screen then type

$ head science.txt

Then type

$ head -5 science.txt

:loudspeaker: 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

$ tail science.txt

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

Searching the contents of a 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

$ less science.txt

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

As you can see, less finds and highlights the keyword. Type [n] to search for the next occurrence of the word.

grep (don’t ask why it is called grep)

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

$ grep science science.txt

As you can see, grep has printed out each line containing the word science.

:loudspeaker: Or has it?

Try typing

$ grep Science science.txt

The grep command is case sensitive; it distinguishes between Science and science.

To ignore upper/lower case distinctions, use the -i option, i.e. type

$ grep -i science science.txt

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

$ grep -i 'spinning top' science.txt

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, you can use more than one option at a time, for example, the number of lines without the words science or Science is

$ grep -ivc science science.txt

wc (word count)

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

$ wc -w science.txt

To find out how many lines the file has, type

$ wc -l science.txt

Summary

code Function
cp file1 file2 copy file1 and call it file2
mv file1 file2 move or rename file1 to file2
rm file remove a file
rmdir directory remove a directory
cat file display a file
more file display a file a page at a time
head file display the first few lines of a file
tail file display the last few lines of a file
grep [keyword file] search a file for keywords
wc file count number of lines/words/characters in file