Introduction to UNIX
Most of the material in this section comes from the UW site…..
http://www.washington.edu/computing/unix/Please go to this site to see a more complete introduction to UNIX and using UNIX at the UW.
New users UNIX Commands Shells UNIX file system
If the Unix operating system is new to you, there are certain commands and characters it is useful to know about since they are used on a regular basis. You should be aware that the entire "Unix User's Manual Reference Guide" to commands is available for viewing online. So, for detailed information about any of the commands described below, as well as all other Unix commands, at the Unix prompt you can enter
mancommandname
Where commandname is the name of the command about which you wish information.
If you are interested in a particular function and it is not a command name, or you wish to see all commands that apply, you can enter
aproposkeyword
Where keyword is the identifying string you wish to know about.
Be careful using this command - if you use something very common as the keyword argument, you will be shown every possible place the string appears. For example, `apropos ls' will show you every command that has the letters ls somewhere in its description, whether these apply to `listing' something or not.
Another source of information is the C&C help notes, of which this note is one. To see a complete list of the available notes enter help -l or help index
To view a particular note, enter
helpnote
where note is the name of the topic.
Remember, UNIX COMMANDS ARE CASE SENSITIVE!
cat - concatenates files and displays them
on your screen
more - displays named file(s), pausing for
each page to be read
ex - invoke basic Unix line text editor
vi - invoke full screen-oriented version
of ex
finger - user information lookup program
ls - list contents of directory
mail - send and receive mail
msgs - system messages and junk mail program
passwd - change login password
ts, tset - set terminal modes; use ts, it is a useful alias
who - who is on the system
DELETE Backspace over and erase the
last character typed in.
^C Interrupt the current program.
^U Kill current line and start over.
^S Pause while printing something.
^Q Continue after pause.
^R Retype the current line.
^W Erase last word typed in.
^Z Suspend job (resume via `fg' -
"More"-ing: Some programs (such as help and man) use a mechanism called "more" to write long files onto your terminal. If you enter the command
more filename
a page of the file `filename' will appear on your terminal, followed by:
--More--
To continue displaying the file, press `d' or the space bar. To stop, type `q' or press ^C.
man yyyy Show UNIX Programmer's Manual entry
on topic `yyyy'
apropos keyword Lists commands relevant to keyword.
msgs Read system messages
msgs 95 Read system messages starting at
number 95.
msgs -3 Read last 3 system messages
ls List files in the current directory.
ls -al Long list of all files in current directory.
(this list includes files whose names
begin with `.')
cat f1 f2 ... Print the files `f1', `f2', ... on
the terminal.
more f1 f2 ... Print the files `f1', `f2', ... on
the terminal, one screenful at a time.
cp f1 f2 Copy file `f1' to file `f2'
ln f1 f2 Link file `f1' to the alias name `f2'
(note that ln provides two names for the
same file, whereas cp makes a separate
copy of the file).
mv f1 f2 Move (that is, rename) file `f1'
to new name `f2'.
rm f1 f2 ... Remove (that is, delete) files `f1', `f2',
...
pwd Give full pathname of current directory.
cd d1 Change to directory `d1'
mkdir d1 d2 ... Make new directories called `d1', `d2', ...
rmdir d1 d2 ... Remove directories `d1', `d2', ...
the directories can be removed only if they
are empty (use `rm' to remove the files
first)
ls d1 d2 ... List files in directories `d1', `d2', ...
a.out < f1 Program `a.out' reads from file `f1'
instead of terminal
a.out > f2 Program `a.out' writes to `f2' instead
of the terminal.
a.out >> f `a.out' appends to file `f' instead
of overwriting it.
a.out <f1 >f2 These may be combined; spaces don't matter.
a.out | b.out The output of `a.out' is the input for `b.out'
a.out & run `a.out' in background
a <f | b >g & Another possible combination.
Computing & Communications has added several commands to its Unix systems:
prt 'prt' is the standard C&C print utility
available on all the C&C computers
and is the preferred way to print file
from any of the C&C systems (use 'prt'
instead of 'lpr'). The 'prt' command is
described in the 'prt' man page.
chkout 'chkout' is a command used to check out
temporary disk space for those times
when your short term need for disk space
exceeds your disk space allocation.
'chkout' is described in 'man chkout'
and 'help chkout'.
ted 'ted' is a full-screen editor that some
people find easier to use than 'vi'.
More UNIX commands
This document provides examples of the use of many of the most common Unix commands. The first thing to remember about Unix commands is that are
case sensitive.For more details on a command see the man page for the command. For example, to see more information about the command 'rm', enter the command
man rm
To display a list of commands related to a topic enter
man -k topic
or
apropos topic
Additional information is available on the C&C Unix mainframes in the form of help notes. To see a list of all available help notes, enter the command
help -l
To see a specific help note, enter
help topic
where 'topic' is a specific topic, such as 'tapes'.
You should also understand that some commands you may be looking for are not part of the basic Unix operating system but, instead, belong to the shell that interprets your commands. The most commonly used shell is the C-shell, which is described in the 'man csh' page. For example, the following commands are described in the 'man csh' page and do not have separate man pages of their own:
repeat
setenv
history
alias
< << >> > | (I/O redirection and piping)
... and many others.
Remember: UNIX COMMANDS ARE CASE SENSITIVE!
passwd ... set a new password for your account
assets ... view information on resource use
by your account, including connectivity
time, cpu use, and disk space. (Available
on C&C systems only.)
DO: TO:
--------------- ---------------------------------------------
pwd ... find out what your current working
directory is
mkdir playdir ... create a new subdirectory called
'playdir'
rmdir junkdir ... remove subdirectory 'junkdir' (must be
empty of files and subdirectories)
cd /usr/bin ... change to '/usr/bin' directory
(directory specification is relative to
the root directory)
cd class/cs108 ... change to a subdirectory named
'class/cs108' (directory specification is
relative to current working directory)
cd .. ... change to directory one level above
current working directory
cd ... change to home directory for the account
you are using
du ... display the number of disk blocks in use
(the total combined size of all files)
in each directory and subdirectory.
DO: TO:
--------------- ---------------------------------------------
ls ... list files in the current working
directory
ls notes ... list file in the subdirectory
named 'notes'
ls -l ... list all files in the current working
directory, along with each file's
permission, owner, size in bytes and date
of last modification.
ls -a ... list files in the current working
directory, including dot files (those
files with names beginning with a period)
ls -F ... list files in the current working
directory, indicating executable files
with an asterisk (*) and subdirectories
with a /
find docs -name \\*\.memo -print
... list all files in the directory
'docs' and any subdirectories of 'docs'
with filenames ending in '.memo'. The
\ is necessary before the * to insure
that is is interpreted as a wild character.
cp file1 file2 ... copy the file 'file1' to a file named
'file2' (original file remains intact with the
same name)
mv oldf newf ... move the file 'oldfile' to a file named
'newfile' (equivalent to renaming a file)
rm badfile ... remove the file 'badfile' (the file is
permanently removed and cannot be recovered)
rm -i *.c ... remove all files in the current directory
with the suffix '.c' and be asked for
confirmation on each file
chmod a+r resul ... grant read access of the file 'resul'
to all users
cat shortfile ... display the file 'shortfile'
more longfile ... display the file 'longfile', a
screenful at a time
head big ... display the first ten lines of
file 'big'
head -25 big ... display the first 25 lines of file 'big'
tail big ... display the last ten lines of file 'big'
tail -25 big ... display the last 25 lines of file 'big'
grep done tasks ... display all lines within file 'tasks'
containing the string 'done'
DO: TO:
--------------- ---------------------------------------------
ps ... list the status of your jobs by
process identifier (PID)
ps -aux ... list the status of all jobs by process
identifier (PID)
jobs ... list the status of all jobs by job
number
<CTRL>z ... suspend the job currently running in
the foreground
bg ... resume the most recently suspended job
into the background
bg %2 ... resume job number 2 in the background
fg %2 ... resume job number 2 in the foreground
fg %3 ... bring job number 3, which is running
in the background, into the foreground
kill %2 ... kill job number 2
kill 1234 ... kill job with PID 1234
DO: TO:
--------------- ---------------------------------------------
prt -printers ... list available printers
sed 's/^/ /' Memo | prt
... shift the file 'Memo' five columns
and send it to the printer. The following
is a detailed description of the command:
sed 's/^/ /' Memo | prt
^ ^ ----- ^ ^ ^
| | | | | |
substitute | | | | |
at beginning | | | |
of each line | | | |
five spaces | | |
file name | |
pipe to |
print
repeat 5 prt class.notes
... print five copies of the files
'class.notes'. The command 'repeat'
is a C shell command.
DO: TO:
--------------- ---------------------------------------------
telnet becker.u ... establish an interactive session on
computer 'becker'
ftp sun.latin.washington.edu
... transfer a file to or from computer
'sun.latin.washington.edu'
DO: TO:
--------------- ---------------------------------------------
who ... find out who is logged on to the
computer
w ... find out who is logged on to the
computer and what they are doing
finger suzz ... display information about user 'suzz'
biff y ... be notified if mail arrives. To turn
off notification, enter the command 'biff n'
pine ... start pine mailer. Pine is an alternative
to 'mail' that many people find easier to use
than 'mail'
DO: TO:
--------------- ---------------------------------------------
cal 6 1990 ... display a calendar of June, 1990.
date ... display current date and time
script ... start recording of all screen
interactions
exit ... stop script recording (text from
recorded session will be in a file named
typescript )
alias dir ls -Fal ... alias 'dir' to represent the command
'ls -Fal'
unalias dir ... remove the alias for 'dir'
alias ... show all current aliases
DO: TO:
--------------- ---------------------------------------------
<CTRL>u Delete entire line
<CTRL>w Delete the preceding word
<CTRL>h Delete the preceding character
<CTRL>c Abort the program currently running
<CTRL>z Suspend the program currently running (use
fg or bg to resume the program in the
foreground or background, respectively)
cc myprog.c > listing
... run C compiler on 'myprog.c' source file,
redirecting compilation messages to a file
named 'listing'. The resulting file would NOT
include any diagnostic messages.
cc myprog.c >& listing
... run C compiler on 'myprog.c' source file,
redirect compilation messages, including
diagnostic messages, into a file named 'listing'.
ps -aux | more ... list all current jobs on the system,
piping the result to more for viewing one
screen at a time
cat frog >> rat
... concatenate the contents of file 'frog'
onto the end of file 'rat'
A Unix shell is a command language interpreter, the primary purpose of which is to translate command lines typed at a terminal into system actions. The shell itself is a program through which other programs are invoked. Although there are several different Unix shells, among them the C shell (csh), the Bourne shell and the Korn shell, the one most frequently used on Blake within Berkeley UNIX is the C shell.
The shell has some built-in functions, which it performs directly, but most commands that you enter cause the shell to execute programs that are external to the shell. This sets the shell apart from other command interpreters, because it is just another user program at the same time that it functions almost exclusively as a mechanism for invoking other programs.
For more information about the C shell, refer to the article ``An Introduction to the C Shell,'' by William Joy, in the Unix User's Manual Supplementary Documents volume. Also see `man csh' online.
One handy thing you can do with the shell is to use standard UNIX commands as building blocks to create your own new commands. To do this, you write a `shell script', which can contain a number of commands, and then the file can be executed as one command.
Following is an example of a very simple shell script, which gives a brief indication of the types of things you might do. To use this feature to its maximum potential, however, you will need to refer to the documentation mentioned above, or other Unix manuals.
Suppose your name is joanx and occasionally you want the system to tell you your user id, what directory you are in, list the files in that directory, and display the date. You want each of these pieces of information to be preceded by an appropriate statement. The individual Unix commands you need are `echo,' `who am i,' `pwd,' `ls,' and `date.' So you would create a a regular text file (let's call it `me') with the following lines in it:
echo you are
who am i
echo The directory you are in is
pwd
echo The files in this directory are
ls
echo The date is
date
You (joanx) can execute the file called me, when you are in the same directory it is in, simply by entering
sh me
When you do this, the following information might be displayed on your screen:
you are
joanx ttyB7 Jun 9 14:51
The directory you are in is
/b2/joanx/mine
The files in this directory are
herfile hisfile myfile ourfile
The date is
Fri Jun 9 16:10:50 PDT 1989
Once you learn to create and use them, you should see that shell scripts are useful Unix tools that might save you a lot of time in your day-to-day computing.
Virtually any command which can be executed at the unix prompt can be executed within a shell script.
Each line of the script file is a single command. There are two exceptions to this statement. The first is when a line ends with a backslash "\\", since the backslash removes the significance of the newline character as a command terminator. Therefore, a backslash at the end of a line is the indication of command continuation on the following line, just as it is at the prompt.
The second exception is when the "<<" I/O redirection symbol is used in a script file. This symbol will be discussed below.
Comments in C shell scripts begin at a pound sign "#" and continue to the end of the line. Since most Unix system support several shells, it is recommended that each shell script start with a comment indicating which shell the script was written for.
Text can be sent to standard output from within a shell script by using the c-shell command 'echo'. This command will print the value of its arguments on standard output appending a newline. The -n option to echo will suppress the newline at the end of the text.
The following script will print out the name and contents of the current working directory.
# print the name and contents of the current
# working directory
echo "This is from a shell script:"
pwd # print the directory name
ls # print the directory contents
The following script will edit a C source code file named "count-c", compile and link it producing an executable version named "count", and finally run count.
# edit compile link, and run
vi count.c
cc count.c -o count
count
There are three ways to execute a c-shell script.
The simplest way to execute a shell script is to used chmod to make the text file executable. The script can then be executed by typing its name if it is in the current working directory or is in the path for that shell.
Executing a script creates a new shell and executes each command in the script within the new shell. When the end of the script file is encountered, the new shell exits. Any changes in the new shell caused by the script are lost when the shell exits.
For example, if the file
/usr/samples/script/change contains...
cd/usr/games
pwd
fortune
Then the command sequence would yield the following output:
saul> cd /usr/samples/script
saul> pwd
/usr/samples/script
saul> chmod +x change
saul> change
/usr/games
To err is human. To forgive, divine.
saul> pwd
/usr/sample/script
Another way to execute a script within the context of a new shell is to run csh and give it the name of the script file as its first argument. This is, in fact, how direct execution is implemented. By executing csh directly, the default csh options can be modified. Then the command sequence would yield the following output:(user input is in bold) (the -x option causes echo to be set, i.e each command will be echoed before it is executed)
saul> cd /usr/samples/script
saul> pwd
/usr/samples/script
saul> csh -x change
cd /usr/games
pwd
/usr/games
fortune
To err is human. To forgive, divine.
saul> pwd
/usr/samples/script
The third way to execute a script will execute it within the context of the current c-shell, using the c-shell command source and giving it the name of the script file as its first argument. Since execution takes place within the context of the current shell, any changes in the shell are retained following the completion of the shell. Then the command sequence would yield the following output:
saul> cd /usr/samples/script
saul> pwd
/usr/samples/script
saul> source change
/usr/games
To err is human. To forgive, divine
saul> pwd
/usr/games
There are several ways to execute commands within shells or at the command prompt.
SEQUENTIAL COMMANDS
A series of independent commands can be grouped together as a single command by separating them by semicolons ";".
PIPES
Pipes "|" also cause the execution of multiple processes from a single command line. With a pipe, the standard output of the process before the pipe is redirected to the standard input of the process after the pipe. This is also covered below, in I/O Redirection.
saul> /fortune | tee temp ; wc temp ; rm temp
Save the whales. Collect the whole set.
1 7 41
INLINE EXECUTION
Grave accents "`" (on the same key as the tilde "~") will force inline execution of the enclosed command. Like the quotation marks "''" and the apostrophes "'", grave accents must be used in pairs. Grave accents are used where a command "is not expected".
saul> set code = ( `ls *.c`)
SUBSHELLS
Any commands enclosed within parentheses are run in a separate shell, similar to the "direct" or "csh" execution of a shell script. As you can see, technically, this is not a means of running a shell script at all, but it is similar. The following sequence of commands illustrates this. Recall the use of the semicolon to separate sequential commands.
saul> cd /usr/samples
saul> pwd
/usr/samples
saul> (cd ; pwd)
/users/unix0
saul> pwd
/usr/samples
saul> cd ; pwd
/users/unix0
saul> pwd
/users/unix0
DEFERRED EXECUTION
There are times when variable substitution must occur before command execution. The c-shell command eval causes execution to be deferred until after variable substitution. Variable substitution is discussed in greater detail in the next section.
Input and output redirection is available within shell scripts.
Input redirection will read from the named file instead of from the terminal. Input redirection uses the symbol "<". Output redirection uses the symbol ">" to create the named file to contain the output of the process. Output redirection can clobber (overwrite) an existing file. Output will be appended to the named file when the output redirection symbol ">>" is used.
Piping connects the output of one process to the input of a second. Piping uses the symbol "|". A filter is a process which is between two pipes. It simply changes the information coming down the pipe.
Standard input for a process can be drawn from the script file itself. This uses the special redirection symbol "<<". The name which follows the redirection symbol is a tag for the end of the input. That is, the contents of the script file will be read as standard input to the process until a input line matching the name following the redirection symbol.
If the file /usr/samples/script/redirect contains:
cd
echo "Here are some commands:"
sort << end > temp
pwd
ls
clear
passwd
end
cat temp
The following is an example of using the 'redirect' script:
saul> cd /usr/samples/script
saul> redirect
Here are some commands:
clear
ls
passwd
pwd
saul> pwd
/usr/samples/script
The UNIX file system
http://www.geek-girl.com/Unixhelp/concepts/strctfile1.html
The standard system directories are shown below. Each one contains specific types of file. The details may vary between
different UNIX systems, but these directories should be common to all. Select one for more information on it. /(root)
|
--------------------------------------------------------------
| | | | | | | |
/bin /dev /etc /home /lib /tmp /usr kernel file
This directory contains the commands and utilities that you use day to day. These are executable
binary files - hence the the directory name bin.Often in modern UNIX systems this directory is simply a
link to /usr/bin.
This directory contains special files used to represent real physical devices such as printers and terminals. One of these files represents a
null (non-existent) device.This directory contains various commands and files which are used for system administration. One of these files - motd - contains a 'message of the day' which is displayed whenever you
login to the system.This directory contains a
home directory for each user of the system.This directory contains libraries that are used by various programs and languages.
Often in modern UNIX systems this directory is simply a
link to /usr/lib.This directory acts as a "scratch" area in which any user can
store files on a temporary basis.This directory contains system files and directories that you share with other users. Application programs,
on-line manual pages, and language dictionaries typically reside here.As its name implies, the kernel is at the core of each UNIX system and is loaded in whenever the system is started up - referred to as a
boot of the system.It manages the entire resources of the system, presenting them to you and every other user as a coherent system. You do not need to know anything about the kernel in order to use a UNIX system. This information is provided for your information only.
Amongst the functions performed by the kernel are: