Working with Files

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.

For our example we will create a file science.txt. Click the down-arrow icon to download the file. Use whatever method you know to place this file into your home directory.

In the space of one hundred and seventy-six years the Lower Mississippi has shortened itself two hundred and forty-two miles. That is an average of a trifle over one mile and a third per year. Therefore, any calm person, who is not blind or idiotic, can see that in the Old Oolitic Silurian Period, just a million years ago next November, the Lower Mississippi River was upwards of one million three hundred thousand miles long, and stuck out over the Gulf of Mexico like a fishing-rod. And by the same token any person can see that seven hundred and forty-two years from now the Lower Mississippi will be only a mile and three-quarters long, and Cairo and New Orleans will have joined their streets together, and be plodding comfortably along under a single mayor and a mutual board of aldermen. There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.

- Mark Twain, Life on the Mississippi

% cd ~/unixstuff

Then at the Unix prompt, type,

% cp ../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 from the parent directory to the current directory, keeping the name the same. To change the name, use

% cp ../science.txt ./newname

Exercise 2A

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

Confirm the file was created:

% ls

Now delete it:

% rm tempfile.txt
% ls

You can use the rmdir command to remove a directory, but only if it is empty. Try to remove the backups directory. You will not be able to since Unix will not let you remove a non-empty directory.

To remove a non-empty directory use

rm -rf directory

You can request confirmation with

% rm -if directory

though this may be tedious. The -i option (inquire) also works for rm

% rm -i myfile

Exercise 2B

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

Displaying the Contents of a File on the Screen

cat (concatenate)

The cat command can show a text file’s contents

% cat science.txt

Be sure to use the correct path to the file. Cat can also join two text files, hence its name.

% cat file1 file2 > file3

THe > sign is a redirection, which we will discuss later.

clear (clear screen)

Clear the screen.

more

The command more prints the contents of a file onto the screen a page at a time. Type

% more science.txt

Press the [space bar] if you want to see another page. Type [q] if you want to quit reading.

The more command is an example of a pager, a program that “pages” through a text file.

head

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

% head science.txt

Now type

% head -5 science.txt

What difference did the -5 make 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

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

Searching the Contents of a File

Simple Searching Using more

Using more, you can search through a text file for a keyword (pattern). For example, to search through science.txt for the word ‘science’, type

% more science.txt

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

/science

The more command 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… 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 other options for grep are: -v (display those lines that do NOT match); -n (precede each matching line with the line number); and -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

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