UNIX Tutorial Two

2.1 Copying Files

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 unixstuff directory.

First, cd to your unixstuff directory.

% cd ~/unixstuff

Then at the UNIX prompt, type,

% cp /usr/include/sys/types.h ./types.h

Note: Don't forget the dot-slash ./ before types.h. Remember, in UNIX, the dot means the current directory.

The above command means copy the file types.h from the /usr/include/sys directory to the current directory, keeping the name the same.

You can accomplish the same thing by typing

% cp /usr/include/sys/types.h .

Like the previous command, it directs the computer to copy the file types.h from the /usr/include/sys directory to the current directory (.), without changing the file name.

Exercise 2a

Create a backup of your types.h file by copying it to a file called types.bak

2.2 Moving files

mv (move)

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. The calling sequence is of the form   mv file1 file2   which results in moving file1 to file2.

This can be helpful when moving a file from one directory to another. We are now going to move the file types.bak to your backup directory.

First, change directories to your unixstuff directory (can you remember how?). Then, inside the unixstuff directory, type

% mv types.bak backups/.

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

The mv command can also be used to rename a file, by moving the file to the same directory, but giving it a different filename.

2.3 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 types.h file then delete it.

Inside your unixstuff directory, type

% cp types.h tempfile.txt
% ls
% rm tempfile.txt
% ls

These commands first copied the file types.h to a copy called tempfile.txt, then showed you the list of files in this directory (notice the new file), then deleted tempfile.txt, and finally showed you the updated list of files in this directory.

You can use the rmdir command to remove a directory (make sure it is empty first). Try to remove the backups directory.

% rmdir backups

Notice that you cannot remove the directory, since UNIX will not let you remove a non-empty directory.

Exercise 2b

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

2.4 Displaying the contents of a file on the screen

clear (clear screen)

Before you start the next section, you may want 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 to the screen. Type:

% cat types.h

As you can see, the file is longer than than the size of the window, so it scrolls past making it difficult to read the file from the beginning.

 

less

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

% less types.h

Press the [space-bar] if you want to see another page, and type [q] if you want to quit reading.

As you can see, less can be more useful for reading long files than cat.

 

head

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

First clear the screen then type

% head types.h

Then type

% head -3 types.h

What difference did the -3 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 types.h

Q. Can you figure out how to view the last 15 lines of the file?

 

2.5 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 types.h for the word 'long', type

% less types.h

then, still in less, type a forward slash [/] followed by the word you want to search for,

/long

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

 

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 long types.h

As you can see, grep has printed out each line of the file types.h that contains the word long.

Or has it ????

Try typing

% grep LONG types.h

The grep command is case sensitive; it distinguishes between LONG and long.

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

% grep -i long types.h

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

% grep -i 'long int' types.h

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 how the results differ. Don't forget, you can use more than one option at a time. For example, the number of lines without the words long or LONG is

% grep -ivc long types.h

 

wc (word count)

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

% wc -w types.h

To find out how many lines the file has, type

% wc -l types.h

Summary

Command Meaning
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
less 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

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M. Stonebank, 9 October 2000,     D.R. Reynolds, 13 January 2009