Review

Here is a review of commands and concepts that we have covered so far.

Commands

We have covered the following commands so far:

Command	Example	Explanation
tree	tree -dfL 1	List directories, full path, one level
cd	cd ~	change to home directory
	cd /	change to root directory
	cd bin	change to bin directory from current directory
pwd	pwd	print working / current directory
ls	ls ~	list home directory contents
	ls -al	list long format and hidden files in current directory
	ls -dl	list long format the current directory
man	man ls	open manual page for the ls command
	man man	open manual page for the man command
cp	cp * bin/	copy all files in current directory to bin subdir
mv	mv oldname newname	rename file oldname to newname
	mv oldir bin/newdir	move oldman to bin subdir and rename to newdir
rm	rm oldfile	delete file named oldfile
	rm -r olddir	delete directory olddir and its contents
touch	touch newfile	create a file called newfile
	touch oldfile	modify timestamp of file called oldfile
mkdir	mkdir newdir	create a new directory called newdir
rmdir	rmdir newdir	delete directory called newdir if empty
echo	echo "hello"	print "hello" to screen
cat	cat data.csv	print contents of file called data.csv to screen
	cat data1.csv data2.csv	concatenate data1.csv and data2.csv to screen
less	less file	view contents of file called file
sudo	sudo command	run command as superuser
chown	sudo chown root:root file	change owner and group to root of file file
chmod	chmod 640 file	change permissions of file to -rw-r-----
	chmod 775 somedir	change permissions of of somedir to drwxrwxr-x
groups	groups user	print the groups the user is in
wc	wc -l file	print number of lines of file
	wc -w file	print number of words of file
head	head file	print top ten lines of file
	head -n3 file	print top three lines of file
tail	tail file	print bottom ten lines of file
	tail -n3 file	print bottom three lines of file
cut	cut -d"," -f2 data.csv	print second column of file data.csv
sort	sort -n file	sort file by numerical order
	sort -rn file	sort file by reverse numerical order
	sort -df file	sort file by dictionary order and ignore case
uniq	uniq file	report or omit repeated lines in sorted file
	uniq -c file	report count of duplicate lines in sorted file

In addition to the above commands, we also have pipelines using the |. Pipelines send the standard output of one command to a second command (or more). The following command sorts the contents of a file and then sends the output to the uniq command to remove duplicates:

sort file | uniq

Redirection uses the > or the >> to redirect output of a command to a file. A single > will overwrite the contents of a file. A double >> will append to the contents of a file.

Redirect the output of the ls command to a file called dirlist:

ls > dirlist

Append the date to the end of the file dirlist:

date >> dirlist

Paths

I introduced the concept of absolute and relative paths in section 2.3. In this session, the goal is to revisit paths (locations of files and directories in the filesystem), and provide some examples. This will be important as we proceed to Bash scripting and other tasks going forward.

Change Directories

The cd command is used to change directories. When we login to our systems, we will find ourselves in our $HOME directory, which is located at /home/USER.

To change to the root directory, type:

pwd
/home/sean
cd /
pwd
/

From there, to change to the /bin directory:

cd bin
pwd
/bin

To change to the previous working directory:

cd -
pwd
/

To go home quickly, just enter cd by itself:

cd
pwd
/home/sean

To change to the public_html directory:

cd public_html
pwd
/home/sean/public_html

To change to the directory one level up:

cd ..
pwd
cd /home/sean

Make Directories

Sometimes we'll want to create new directories. To do so, we use the mkdir command.

To make a new directory in our $HOME directory:

pwd
/home/sean
mkdir documents
cd documents
pwd
/home/sean/documents
cd
pwd
/home/sean

To make more than one directory at the same time, where the second or additional directories are nested, use the -p option:

mkdir -p photos/2022

Remove or Delete Files and Directories

To remove a file, we use the rm command. If the file is in a subdirectory, specify the relative path:

pwd
/home/sean
rm public_html/index.html

To remove a file in a directory one level up, use the .. notation. For example, if I'm in my documents directory, and I want to delete a file in my home (parent) directory:

cd documents
pwd
/home/sean/documents
rm ../file.txt

Alternatively, I could the tilde as shorthand for $HOME:

rm ~/file.txt

To remove a file nested in multiple subdirectories, just specify the path (absolute or relative).

rm photos/2022/05/22/IMG_2022_05_22.jpg

Remember that the rm command deletes files and directories. Use it with caution, or with the -i option.

Copy Files or Directories

Let's say I want to copy a file in my $HOME directory to a nested directory:

cp file.txt documents/ICT418/homework/

Or, we can copy a file from one subdirectory to another. Here I copy a file in my ~/bin directory to my ~/documentsdirectory. The ~ (tilde) is shorthand for my $HOME directory.

cp ~/bin/file.txt ~/documents/``

Move or Rename Files or Directories

Let's say I downloaded a file to my ~/Downloads directory, and I want to move it to my ~/documents directory:

mv ~/Downloads/article.pdf ~/documents/

Or, let's say we rename it in the process:

mv ~/Downloads/article.pdf ~/documents/article-2022.pdf

We can also move directories. Since the commandline is case-sensitive, let's say I rename the documents directory to Documents:

mv ~/documents ~/Documents

Conclusion

Use this page as a reference to the commands that we have covered so far.

Linux Systems Administration