Common UNIX Commands

This document presents a brief description of commonly used UNIX commands. The list is a small subset of the available commands and utilities. For more information on these commands and others not listed here, consult the on-line manual pages (see the man command).

Most people only learn UNIX to do specific things, like to publish a Web Page. To that effect, below are listed the commands that are needed to do the things necessary on "cs.wbc.edu". Just click, and it will take you to those commands.

Common Commands and their MS-DOS equivalents.

  1. ls = dir
  2. mkdir = mkdir
  3. cp = copy
  4. mv = move
  5. pwd = (tells you where you are)
  6. cd = cd
  7. exit = (exit from cs.wbc.edu)

Note: Enter the commands below exactly as shown (including spaces and upper- or lowercase). Arguments or parameters to the commands are shown in italics and should be replaced with your own values at the time that you execute the command (e.g. the name of a file is an argument to the cat command rather than the word, file).

alias alias-term command-string
The alias built-in shell command allows the entering of shorter or easy-to-remember names to execute longer or hard-to-remember commands. The command is entered to set alias-term equal to command-string. If command-string has spaces in it, single quotes should be around the string. For example, entering alias dir='ls -al' will allow ls -al to be executed whenever the dir command is entered (thus easing the transition to UNIX for the MS-DOS users). Each user can put these alias commands in their .bashrc file to have the aliases automatically set each time the user logs in. Entering alias by itself will list all the aliases currently set for the user.
cal
The cal command displays the current month. If you specify the year, e.g. cal 1996, it will display all the months for that year. The -j specifies the display to be in the Julian calender, e.g. cal -j 1996.
cat file
The cat command displays the contents of the file named by file. If the file is large, all but the last screenfull of lines will scroll off the screen too quickly to read. To display the file a screenful at a time, pipe the output to the more or less commands.
cd directory
The cd command moves you (changes your current working directory) to directory. Entering cd without the directory argument will move you to your home directory.
Examples:
cd /usr/bin
moves you to the bin directory inside of the usr directory.
cd ..
moves you to the parent directory of your current directory.
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chmod permissions path
The chmod command changes the access permission associated with a file or directory ("file" will be used here to refer to either a file or a directory).

Each file has three types of access: read (r), write (w) and execute (x). In a ls -al file listing, the abbreviations appear in the columns on the left. To see the contents of a file, the file must have read (r) permission. To change the contents of a file (e.g. saving changes after editing), write (r) permission must be enabled. To execute a command by entering the name at the UNIX prompt, the file must have execute (x) permission. To access a directory, the execute (x) permission must be granted for that directory. If a given type of access is not permitted, it will show up as a dash (-) rather than r, w or x in the ls -al listing.

The access to a file can be controlled separately for three sets of users: the owner of the file (u), a limited group of users (g), and everyone on the system (o). In a ls -al file listing, the first three columns (starting in column two of the listing) are the r, w and x access allowed for the owner, the second three are the access allowed for the group and the third three are the access allowed for everyone else.

Permissions can be specified in numeric format or using the abbreviations above. For the numeric format, three numbers are specified where each number represents the access granted for one of the three sets of users. Each permission number is determined by adding up the value associated with each type of access: r = 4, w = 2 and x = 1. For example, the value 7 grants all access, the value 5 grants only read and execute access but not write access and the value 0 does not allow any access to the file. The numeric access specification is an absolute one; all three types of access for all three sets of users are reset according to the new permissions.

Examples:
chmod 640 .bash_profile
grants read and write permission (6) to the owner of the file, read-only permission to the group, and no permissions for everyone else. The would appear in a file listing as rw-r-----.
chmod 777 .
grants all access to the owner, group, and everyone for the current working directory.
The permissions can also be specified using abbreviations rather than numbers. Using this method, some of the permissions can be changed without affecting others. The permissions format is <u, g or o> <+ or -> <r, w or x>. The + adds the access indicated to the file without affecting the other permissions. The - removes the access from the file.
Examples:
chmod u+rw report
adds read and write permission to the file, report, for the owner of the file. Access for the group and everyone is unchanged.
chmod +x somecommand
adds execute permission to the file, somecommand, for all three sets of users.
chmod go-rwx private.file
removes all access to the file, private.file, for the group and everyone and leaves the owner's access unchanged.
See file and directory permissions in UNIX Concepts
chown username path
The chown command changes the ownership of the file or directory, path, to user, username. Both the user-ownership and the group-ownership may be changed at once by specifying user.group for the username parameter. One must have root privileges to do this so this command will not be too useful for most users. If you really want to own someone else's file that you have read-access to, make a copy of the file using the command, cp.
cp file1 file2
The cp command creates an identical copy of the file, file1, and names the copy, file2. Note that the ownership of file2 will be set to whoever does the cp command.

Back to Common Commands...

date
The date command displays the current date and time. Use date -u to see the time in Greenwich Mean Time (GMT), universal time.
diff file1 file2
The diff command compares the contents of two text files and displays the differences. The lines preceded with < are from file1. The lines preceded by > are from file2. Each section of differences is separated by ---.
du options
The du command summarizes disk usage. du entered on the command line with no options will return the size of all the directories beneath the current working directory. du with the -s option will return a summary of all the directories suppressing all output but the total. du with the -a option will return not only the directories but the individual files.

This command will report the amount of the 5 MB of disk space you have used if issued from your home directory

exit
The exit command terminates the current UNIX shell. If you started this UNIX session (shell) with either the rlogin or telnet command from within another session, exit returns you to your previous session. If not, exit usually just closes your window (either an xterm window or terminal program window) or returns you to a login: prompt.

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chfn  [Note: currently disabled]
The chfn, or change finger command allows you to modify the information in the password file that people can obtain about you using finger.

Information that can be change is:

You may change the information to whatever you like, as often as you like, by telneting to the CS Server and running this program.

This modifies the information that is in the /etc/passwd file that has the permissions to allow it to be world readable. UNIX reads this file to determine things like who you are, what is your home directory, the command shell you use, what program or processes you are allowed to run, your username and your password (which is encrypted for your protection).

finger name@address  [Note: currently disabled]
The finger command displays information about user accounts with names (usernames or proper names) matching name on the machine identified by address. The argument name may be a known username or a first or last proper name without any spaces although this varies from machine to machine. When fingering @cs.wbc.edu, use the userid, e.g.finger jtpolk@cs.wbc.edu.

The finger command may not work if the remote machine is not a UNIX machine (although most multi-user machines have finger capability these days). If only the @address, portion of the argument is used, all of the users currently logged into the remote machine may be displayed, e.g.finger @cs.wbc.edu. If no argument is specified, all of the users currently logged into your machine are shown (see also the who command).

An electronic mail address can often be verified or determined using the finger command. For example, if you do not know if a person's address is correct, use the finger command with what you think is their email address.

If you are concerned about the information that can be obtained by others about you, use the chfn command to change that information.

fortune
The fortune command has no value other than to give you tidbits of wisdom! e.g.
If you want such wisdom every time you logon cs.wbc.edu, simply add it to your .bash_profile which is read by your command shell (bash) when you login to "cs.wbc.edu".
ftp hostname
The ftp command will connect you to another computer to either get a file(s) from the remote machine or to put a file(s) onto a remote machine.

Once ftp has made a connection with the remote machine it will prompt your for your password and username, just like you would with telnet. If you do not have an account on that machine., then login in with anonymous as your password and your email address in the form of username@ hostname as your password. This is known as anonymous ftp.

ftp> Once at this prompt the commands are:

Little known tip: To see the contents of a text file on a remote machine without having to download it first to the local machine, the command is:

get filename -.

The ''-'' pipes the contents of the file to the screen.

grep pattern file  [Note: currently disabled]
The grep command searches one or more files, specified by file, for the text string specified by pattern. For example, grep 'dna' seqfile1 will list all lines found in the file, seqfile1, which contain the text "dna". Grep is usually used to search for text in several files at once, e.g. grep 'dna' * will perform the same search on all the files in your current directory (see wildcard characters for an explanation of *).
head file
tail file
The head and tail commands list the first (head) or last (tail) ten lines of your file. The number of lines listed may be varied by including -n number-of-lines option. For example, head -n 50 report1 will list the first fifty lines of the file report1.
kill id-number
The kill command terminates the process with the id, id-number. The process id can be determined with the ps command. Generally, the kill command is the last method tried to terminate a running program. If a normal kill (a kill without any kill-level option specified before the id-number) does not remove the process, including the -9 option will usually annihilate it (unless it is a zombie process -- in which case it doesn't exist so it can't be killed (confused yet?)) e.g. kill -9 18201 is a "sure kill" of process number 18201.
less file1
The less command displays the contents of the text file, file1, a screenful at a time, pausing at the end of each screen until the user presses one of a few special keys. When the display pauses, the user may press:
less may also be used at the end of a "pipe" to cause the output from another command to be paused a screen at a time. This is useful when a UNIX command produces a lot of output too fast for the user to see before the output scrolls off the screen. For example, the ls -al command often produces long directory listings which are better viewed a screen at a time by entering ls -al | less. Also useful when displaying the calender year using the cal command.

For a less powerful version of this command see more.

ls pattern
The ls command lists the files and directories in a directory. If pattern is the name of a file, only that file (or files if wildcards are used) is listed. If pattern is a directory name, the contents of that directory are listed. If pattern is omitted, all the files and directories in your current directory are listed. The output of the ls command may be piped into the more command to pause the listing after each screenful of text (e.g. ls -al | more).
Here are a few of the options for the ls command (for a complete list, see the ls man page):
-a
lists all files in the current directory. Without this option, filenames that begin with a period (such as .bash_profile, .lessrc, and ..) are not shown).
-l
lists the filenames in long format. This format includes the protections or permissions (changeable with chmod) on each file and the owner of the file.
-g
adds the group ownership of the file to the information displayed with the -l option described above.
-F
highlights directories with a trailing /, executable files with a trailing * and symbolic links with a trailing @ in a listing.
Examples:
ls
lists every file (except those filenames that begin with a period) in in the current directory.
ls -al /bin
lists all files in the /bin directory in the long format.
ls -laFg
lists all files in the current directory in long format (including group ownership), highlighting directories, executable files and symbolic links.
Back to Common Commands...
man command
The man command displays the standard UNIX manual page for the command you specify. These pages may be somewhat cryptic for some users but generally tell you all you would ever want to know about the command.
mkdir dir1
The mkdir command creates the directory, dir1, within your current directory (unless the specification of dir1 begins with a /).

Back to Common Commands...

more file1
The more command displays the contents of the text file, file1, a screenful at a time, pausing at the end of each screen until the user presses one of a few special keys. When the display pauses, the user may press:
more may also be used at the end of a "pipe" to cause the output from another command to be paused a screen at a time. This is useful when a UNIX command produces a lot of output too fast for the user to see before the output scrolls off the screen. For example, the ls -al command often produces long directory listings which are better viewed a screen at a time by entering ls -al | more.

For a more powerful version of this command see less.

mv name1 name2
The mv command moves and/or renames the file or directory, name1. If name2 is an existing directory, name1 will be moved (not copied) into the directory, name2. If name2 is not an existing directory, name1 (whether it be a file or directory) will simply be renamed into name2. It is possible to move and rename name1 at the same time if name2 is a new name within an existing directory. Any file file already existing with name2 will be overwritten by the renaming or moving of name1 unless mv -i is used, which asks the user for confirmation of destruction of existing files.

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passwd
The passwd command changes your UNIX login password. After entering the command passwd, you will be asked to enter your old password, then the new password that you want to change to, and then the same new password again. You are asked to enter the new password twice to assure that you have typed it correctly. None of the passwords you enter will be displayed on the screen as you type them and your password is encrypted for your protection.

The CS Server Users  will want to read special instructions.

ps
The ps command displays a list of the processes currently running on the machine that you are logged into. If no arguments are entered with the ps command, only the "important" processes, that you own (i.e. that you are running) are displayed. The -a option includes processes owned by others in the list. The -g option includes all processes, not just "important" processes. The -u option provides more information for each processes than is printed by default.
Examples (note that the dash in a ps option is not required):
ps
List all the processes running that you own (minimal information).
ps u
List all the processes running that you own (lots of information).
ps a
List all the processes running on this machine no matter who owns them.
To terminate a process, see the kill command.
pwd
The pwd command displays the full path of your current working directory. In other words, it tells you what directory you are in.

Back to Common Commands...

rlogin address This command has largely been superceded by telnet. See it instead.
The rlogin command logs into another machine specified by address.

The -l username option allows you to specify a username to attempt the remote login with. If this option is omitted, your current username is used by default. Examples: 

   rlogin cs.wbc.edu
logs you into the machine named cs.wbc.com with your current username 
   rlogin cs.wbc.edu  -l smith
logs you into the machine named "cs.wbc.edu" as user smith (of course, you must know smith's password). You can close the connection from the remote machine by entering the command,exit.
rm yourfile
The rm command removes the file, yourfile, permanently from the filesystem. This cannot be undone so be careful when using wildcards in the file specification. Use rm -i to force user-confirmation of each file to be removed. Using rm -r somedir will remove the subdirectory somedir as well as all the subdirectories and files within that subdirectory.

Note: Be careful! If you mean a to delete bunch of files with the extension of *.bak using the command of rm *.bak and instead enter rm * .bak (adding a space between the wildcard ''*'' and the file name extension .bak) it will first remove ALL files then go looking for a file named .bak and issue an error message that it cannot find it.

rmdir dir1
The rmdir command deletes the empty subdirectory, dir1. To delete non-empty subdirectories, see rm -r.
talk name@address
The talk command allows you communicate with another user using your terminal. When first called, talk sends the message:

Message from TalkDeamon@his_machine...
talk: connection requested by your_name@your_machine.
talk: respond with: talk your_name@your_machine.

And they respond with:

talk your_name@your_machine

To end the session hit CTRL-C.

To find out if someone you wish to talk to is available use the who or finger commands.

tail file
See head.
telnet address
The telnet command logs into another machine specified by address.

The -l username option allows you to specify a username to attempt the remote login with. If this option is omitted, your current username is used by default. Examples: 

   telnet cs.wbc.edu
logs you into the machine named cs.wbc.edu with your current username 
   telnet cs.wbc.edu  -l smith
logs you into the machine named cs.wbc.edu as user smith (of course, you must know smith's password). You can close the connection from the remote machine by entering the command,exit.
vi yourfile
vim yourfile
The editor vi is on every UNIX machine, so it should be mentioned. It's also known, on Linux machines as elvis, and there is a version called vim (Vi IMproved). I perfer vim over vi (aka elvis) because there is some on-line help. Before using either vi or vim, I would strongly recommend that one telnet into cs.wbc.edu and issue the following command:

vim /u/b/bbcomp/vitutor/tutor

It is a short tutorial on the editor(s) and almost all the basic commands are the same. There are things you have to know first.

This is the editor that you want to use for editing your .bash_profile and other dot files in you home directory. See the also man pages for either elvis or vim.
wc yourfile
The wc command counts the number of words or characters and lines in your file. If the -l option is used, only the number of lines is counted.
who
The who command displays a list of who is logged on to the system and where they are logged on from. See also finger.