Department of Electrical Engineering

Unix - commands

• Change password
• Move
• View files
• Move and Copy files
• Remove files
• Help functions
• Communication
• User information
• Disk usage
• Programming
• Printing
• File protection

Change password

The command 'passwd' lets you change your password.

Movement in the filestructure

The 'cd' command lets you change working directory. It gives you the opportunity to 'walk' around in the filetree, both up and down in the tree.

cd directory	Changes working directory to directory.
cd ..	Goes up a level in the file structure
cd ../../	Goes two steps up in the file structure
cd ~	Goes to your home directory from all places in the file system
cd ~aaabb123	To go to the home directory of user 'aaabb123' from all places in the filesystem.
pwd	Shows the current working directory.

Listing files and directories

The 'ls' command lets you list files and directories

ls	Lists all files and catalogues (directories) in a directory.
ls -l	Lists all the files and directories, each on a new row, and gives you information about the current protection (the rights to read, write and execute) of the files and directories.
ls -a	Lists all files, directories and system (hidden) files which begin with a dot.
ls -t	Shows the files in time order from when they were last changed.

The 'more' command lets you see the content of a file.

more file	Lists the content of a file on screen. If the file is long you can scroll one page a time using the space bar.
less file	Similar to more. (less is more)

Moving and copying files

cp fromfile tofile	Copies the file fromfile and names the copy tofile
cp ~aaabb123/testfile .	Copies the file testfile located in the home directory of user 'aaabb123' to current working directory, this is the function of the dot at the end. If I stand in my home directory and my loginname is 'bbbaa123' the dot represents '~bbbaa123'.
mv fromfile tofile mv fromdirectory todirectory	Moves (or renames) a file or a directory, and all files in that directory.

Creating and removing files and directories

mkdir directory	Creates a new directory, in current directory, named directory.
rm file	Removes file Warning! A very powerful command!
rm -r directory	Removes directory and everything in it, ie this command can remove a whole filetree! Warning! A even more powerful command!

Help functions

man command	Shows manualpages about the command. Very useful!!
man -k keyword	Searches for a command based on keyword.
whatis command	Displays breif information about the command.

Communication

ssh -l username login-computer	Lets you log on to the login computer from outside (or inside). The session is ended with 'exit'. In comparison to telnet, ssh encrypts the communication with the other computer.
talk user@address	Lets you communicate with another user. The computer will tell if the user refuses to answer or if he isn't logged on The session is ended with

Subcommands in SSH:

scp fromfile hostname:tofile

Similar to cp, but the session is encrypted. Works between unix-systems that use ssh.

User Information

whoami	Returns your userID.
who	Brief information about other logged on users.
w	Detailed information about other logged on users.
users	Displays the userIDs for logged on users.
finger name	Information about a user, name can be either the real name or userID.
tty	Displays your terminal name.

Disk usage

df	Information about used and available disk space in the system.
quota -v	Returns information about disk quota and disk usage.
du	Disk usage for files and directories in the file hierarchy.
du -s file	Returns the total sum of disk usage for each of the specified files.

Programming

cc file.c	Compile 'file.c' to a C program
lint file.c	Validate a C program
indent infile outfile	Format a C program
cxx file.C	Compile a C++ program
pc -L -C -H -g -o file.p exefile	Compiles 'file.p' to a Pascal program 'exefile'
script (run program)exit	Allows you to run a program and store it in a file. The file will be called 'typescript'
dbxtool program &	Let's you debug program
	Indent line (In emacs)

Printing

When you print a document it is transferred to a printer and placed in a job queue.
If a printer is malfunctioning you can easiely override the printer and print your document on a different printer. This is done by adding the argument -P plus the printername to the print command eg, 'ls -Pprintername file'

Be sure to check the printer queue before you print your document!

lpr [-Pprinter] file	Prints file. If the argument '-P' and the name of a specified printer is given the file is directed to the specified printer
lpq [-Pprinter]	Shows the current printer queue and the number of the jobs
lprm [-Pprinter] jobnumber	Removes a specified job
lprm [-Pprinter]	Removes all your jobs in the printer queue

Rights and protection

chmod mode file	Changes the protection for a file, and gives you, a group or the world right to read, change or execute the file depending of the chosen mode. mode represents by [who] operator [permissions] (see below).
chmod a+r file	Allow read permission to everyone for the file.
chmod a=rwx file	Allow everyone to read, write and execute the file.

Represents	Symbol	Explanation	Rights to:
Who	u	user's permissions	the owner of the file
Who	g	group's permissions	the group the file belongs to
Who	o	others' (world) permissions	all that have access to the computer system
Who	a	all permissions (user, group, and other)	default, but the file mode creation mask is taken into account.
Operator	+	add permission	if permissions is omitted, nothing is added
Operator	-	take away permissions.	if permissions is omitted, do nothing.
Operator	=	assign permissions absolutely.	if who is omitted, clear all file mode bits, if who is present, clear the file mode bits represented by who
Permission	r	read permission	add or take away read permisions for the file
Permission	w	write permission	add or take away write permissions for the file
Permission	x	execute permission	add or take away execute permissions for the file

Pipe

By using pipes in UNIX input and output to/from a program can be directed from/to a file. This is done by using '<' and '>'. For example, if you would like to save the information from a command, say 'lpq' you can simply write:

ra>lpq > que.txt

This command takes the result produced by the 'lpq' command and puts it in the file que.txt. If we just want to add new information to an already existing file we use '>>' insted. Example:

ra>lpq >> que.txt

Another example is a program that reads input from a specified file and writes the result in a different file. Imagine you have created a program that sorts three names by letters in alphabetic order called 'Sort'. This program asks us for the names, sorts the names and finally prints the result. We can use one file as input (names.txt in the example below) and another file as output (result.txt) if we don't want the result on standard output (normally the screen).

ra>Sort < names.txt > result.txt