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Chapter 2: Basic File Operations
2.1 Copying Files
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
cd to your unixstuff directory:
Then at the UNIX prompt, type,
(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 /fslapps is an area where supercomputing applications are stored and every user has read access to this area.)
Create a backup of your science.txt file by copying it to a file called science.bak
2.2 Moving files
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 unixstuff directory (can you remember how?). Then, inside the unixstuff directory, type
ls backups to see if it has worked.
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 science.txt file then
Inside your unixstuff directory, type
$ 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
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!
Create a directory called tempstuff using
, then remove it using the
2.4 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
This will clear all text and leave you with the $ prompt at the top of the window.
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 writes the contents of a file onto the screen
a page at a time. Type
[spacebar] if you want to see another page, type
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,
used in preference to
cat for long files.
head command writes the first ten lines of a file to the screen.
First, clear the screen, then type
What difference did the -5 do to the head command?
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?
2.5 Searching the contents of a file
Simple searching using less
less, you can search though a text file for a keyword (pattern).
For example, to search through science.txt for the word 'science',
then, still in
less (i.e. don't press [q] to quit), type a forward
[/] followed by the word to search
As you can see,
less finds and highlights the keyword. Type
to search for the next occurrence of the word. You can also hold down
[N] to search for the previous occurrence of the word.
grep is one of many standard UNIX 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?
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
||copy file1 and call it file2|
||move or rename file1 to file2|
||remove a file|
||remove a directory|
||display a file|
||display a file a page at a time|
||display the first few lines of a file|
||display the last few lines of a file|
||search a file for keywords|
||count number of lines/words/characters in file|
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