The UNIX/BASH Command Line

The command line is offered by a program called your 'shell'.
Your shell by default is called 'bash', the Bourne Again Shell.
Bash could be replaced by another program if you wanted.
Standard commands are ...

Command	Example	Works with STDIN/OUT	Function
ls	ls /tmp	Both	List files (like dir)
ls -l	ls -l /tmp	Both	List files long format
cp	cp src dest	None	Copies files
mv	mv oldname newname	None	Moves or changes the name of a file. Cannot move a directory across between filesystems.
rm	rm oldfile	None	Deletes a file
rm -rf	rm -rf /	None	Deletes an entire subtree. Can wipe out your whole hard drive!!
df	df	Out	Shows free disk space. Shows all filesystems mounted
du	du /tmp	Out	Shows space used by a subtree Requires permissions to read the subtree. Can be slow on big subtrees.
cd	cd	None	Change current dir to home dir.
cd	cd /tmp	None	Change current dir to given dir.
chmod	chmod a+rwx filename	None	Change permissions. Choices for the first letter are a -- all, everyone g -- group u -- yourself. The owner of the file o -- other. People not the owner and not in the group Choices for the second letter are r -- read for a file, list for a directory w -- write for a file, change for a directory x -- execute for a file, access with a known filename for a directory
chmod -R	chmod -R go-rwx .	None	Change permissions for a whole subtree.
chown	chown randy /home/randy	None	Change owner. You must be root to use this command. Being the owner of the file is not enough!
chown -R	chown -R randy /home/randy	None	Changes a whole subtree.
less	less /tmp/README	In	Shows file to the screen.
grep	grep BUGS /tmp/README	Both	Shows lines containing the pattern to the screen.
grep -v	grep -v BUGS /tmp/README	Both	Shows lines NOT containing the pattern to the screen.
cat	cat file1 file2	Both	Concatinates the files.
whoami	whoami	Out	Tells your current username.
su	su randy	None	Changes your current username. requires a password for everyone except root.
time	time du /tmp	Out	Tells how long the command takes to run.
sort	sort /tmp/file-list	Both	Prints files in alphabetic order. (-r reverses order).
sort -n	sort -n /tmp/list-of-numbers	Both	Prints files in number order. (-r reverses order).
head	head -20 /tmp/list	Both	Prints only the first twenty lines.
tail	tail -20 /tmp/list	Both	Prints the last twenty lines.

Commands can be combined.

To run commands consecutively, try seperating them with a semi-colon.
ls; df; du

To run commands simultainiusly, seperate them with a '&'.
rm -rf /tmp & rm -rf /junk

To run commands and not wait for them to finish, end the command line with a '&'.
rm -rf /junk &

To put the output of one command into the input of another, seperate them with a pipe.
ls | sort

To place the output of a command into a file, use a greater-than symbol.
ls > file-list

To have a command read from a file, use a less-than symbol.
sort < file-list

Questions

How do I make a folder named 'fred'?

How do I copy the file /etc/passwd into that folder?

The file /etc/passwd lists all users. Who is the first user alphabetically?

How would you see all files that start with an “a” in /usr/bin?

How would you count them?