Computer Labratories : Unix Introduction & Quick Reference

A few features to get you started with UNIX are described below.

Files and Directories

In UNIX, information is stored in files and directories. Files have names, such as thesis or report.nov19 . Because UNIX uses special characters for special purposes, it is best to use only letters, digits, periods, and underscores in file names.

Files are created by various UNIX commands. You can save your mail messages in files. You can also create text files with an editor.

Files are located in directories . Directories can contain other directories, which are called subdirectories . The directory containing a subdirectory is known as the parent of the subdirectory. Each account has a main directory known as its home directory .

Commands

You can enter UNIX commands by typing the command after a prompt such as "%" and the pressing the <Return> key. For example, type: 
             %
            
              ls
and then press the <Return> key. The ls command lists the names of files in the current directory.

The mkdir command is used to create directories. For example, 

               %
              
                mkdir letters
creates a directory named letters .

Basic file manipulation commands include mv for moving or renaming files, cp for copying files, lpr for printing files, and rm for removing files. The cd command is used to change from one directory to another. For example, the command 

               %
              
                cd letters
moves you to the letters subdirectory, and 
               %
              
                cd
moves you to your home directory.

Special Characters

Special characters may be used in commands to match existing file and directory names. The asterisk is used to match an arbitrary string of characters. For example, 
             %
            
              ls let*
will list all of your files in the current directory beginning with "let" and 
             %
            
              ls *old
will list all files ending with "old".

A question mark is used to match any single character; for example, 

               %
              
                ls ab?de
will match and list files named " ablde ," " abcde ," and " ab.de ," but will not match files named " abde " or " abccde ".

Redirection

Commands normally display results on the screen; this output may be redirected to a file by using the redirection ( > ) symbol. For example, the who command lists the current users on the system. The command 
             %
            
              who > save_who
writes the output of who into the file save_who . Redirection using ( > ) will not overwrite an existing file. To do that, use ( >! ): 
             %
            
              who >! save_who
To append to the end of an existing file, use two redirection characters ( >> ) instead of one.

Output of one command may be used as input to another command by using the pipe ( | ) symbol. For example, 

               %
              
                who | wc -l
shows how many users are logged in by using wc -l to count the lines in the output of who.

History

The history command displays a numbered list of the last twenty-five commands entered. You can repeat a specific numbered command in the list. For example, 
             %
            
              !35
repeats the command numbered 35. Also, you can repeat the last command that began with "str" by typing the following: 
             %
            
              !str
You can repeat the last executed command in the list by typing: 
             %
            
              !!

For more Information

Information about UNIX commands is available via the man and apropos commands. Type 
             %
            
              apropos
              
                topic
to find manual entries relating to "topic," and 
             %
            
              man
              
                command
to find the manual entry for "command".

Many introductory books on UNIX are available in bookstores and libraries.

Quick Reference

Commands may need additional information, such as file or directory names, which are typed immediately following the command name. Clarification and syntax for any command is available by typing man commandname after the "%" prompt and then pressing <Return>.

Basic File Commands:
cat concatenate or display files cp copy files
ls list file names ls -l list file names, sizes, attributes
mv move or rename files rm remove files
Other File Commands:
diff compare two files fmt simple line adjuster for mail
head display the first ten lines of a file tail display the last ten lines of a file
less display file one screen at a time more display file one screen at a time
grep scan a file for a pattern sort sort/merge utility
wc count lines, words, characters in file wc -l count lines in file
Commands:
cd change to a different directory mkdir make a directory
pwd print the current directory's name rm remove a file
rmdir remove empty directory rm -r remove a directory and all files in that directory
Information Applications:
apropos locate commands by keyword man display entries from the online manual
Controlling Applications:
fg restart a suspended command jobs display suspended jobs
kill kill a command ps display commands with process numbers
^c interrupt currently running process ^z suspend currently running process
^s stop output on screen ^q continue output on screen
Miscellaneous:
chfn change information shown by finger clear clear screen
date display date and time finger show information about users
lpr send file to printer passwd change password
who tell who is logged in whatis one-line description of a command
look give correct spelling for words beginning with given word-part
spell obtain list of misspelled words in a file ispell interactive spell checker
history list most recent shell commands logout log out from a UNIX session
pico, vi, jove, emacs edit a file pine, mail, Mail read/send email

Last modified: October 6, 1996