University Computing Services

A brief guide to using UNIX on UCS computers at Florida State University.

If you need additional help, contact the Technology ServicesHelpdesk.

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Commands

Some of the commands available under Unix are listed below. For additional information, see the on-line manual pages.

Directory Commands
cd path	Changes directory to path
pwd	Shows current directory
ls path	Lists contents of directory path
mkdir path	Creates directory path
rmdir path	Removes directory path
File Commands
cp file newfile	Copies file to newfile
mv file newfile	Renames file
mv file directory	Moves file into directory
rm file	Removes file
ln file1 file2	Adds a link to file1
cat files	Types files to screen
more file	Types file, a page at a time
head file	Types top lines of file
tail file	Types bottom lines of file
sort file	Sorts file
find	Finds files
grep pattern file	Searches file for pattern
chmod	Changes file access permissions
umask	Sets default file access permissions
rcp	Copies files between Unix hosts
ftp	Copies files between Internet hosts
tar	Archives files
compress	Compresses file
uncompress	Uncompresses file
pack	Compresses file
unpack	Uncompresses packed file
pico	Invokes pico screen editor
ed	Invokes ed line editor
vi	Invokes vi screen editor
emacs	Invokes emacs screen editor
sed	Invokes stream editor
awk	Scans and processes patterns
file file	Shows the type of file
diff file1 file2	Compares file1 and file2 for differences
du	Displays user's disk usage and availability
df	Displays disk space information
Other Commands
exit	Logs out
passwd	Changes password
groups user	Shows the groups user belongs to
man command	Types on-line manual pages for command
who	Shows logged in users
finger	Shows logged in users
date	Prints day of week, date, time
elm	Read or send electronic mail messages with elm

Some points to remember about Unix commands:

• Unix is case sensitive: upper- case characters are distinct from lowercase characters in commands and file names. Unix command names must be entered in lower case.

• Unix command names cannot be abbreviated.

• A Unix command can be continued to another line if the last character in the line (the character immediately preceding the carriage return) is a backslash (\).

• Several commands can be submitted on the same command line, separated by semicolons (;).

• Many non-alphabetic characters have special meanings to shells. A summary is provided below.

• The Korn shell, Bourne shell, and C shell all provide means to create new names for commands or sequences of commands.

Special Characters

A number of characters have special meanings when they are included in commands issued to a shell:

Special Characters in Shell Commands
$	Indicates variable substitution
*	Matches any string in a file name
?	Matches any single character in a file name
[]	Matches any of the enclosed characters in a file name
\	Turns off the meaning of the immediately following special character
'	Enclosing single quotes turn off the special meanings of all characters
"	Enclosing double quotes turn off the special meanings of all characters except $ and backquote
`	Enclosing backquotes (grave accent) around a command name supply output from the command as an argument to another command
&	Executes preceding command in background mode
;	Separates multiple commands on one line
<	Redirects the contents of a file into a command as standard input
>	Redirects the standard output of a command into a file
>>	Appends the output of a command to the end of a file
|	Output of one command becomes input of another command (pipe)
()	Groups commands in subshell
{}	Groups commands in current shell
||	Executes the second command only if the first fails
&&	Executes the second command only if the first succeeds
~	User's home directory (C shell and Korn shell)
:	Extracts part of path variable (C shell only)
!	History recall (C shell only)

Examples of the use of many of these characters appear in this manual. The chapter is shown in brackets ({}).

Input and Output Redirection; Pipes

In Unix, the input that a command usually accepts from a terminal keyboard is called "standard input" (stdin), and the output that it normally sends to the user's screen is called "standard output" (stdout). "Standard error" (stderr) is error information normally directed to the terminal screen. Unix allows the user to redirect standard input, output, and error information to files.

Redirecting Standard Input, Output, and Error

The "redirect input" symbol (<) instructs the Unix shell to take a program's standard input from a file instead of the terminal. The usage is

% command [options] [arguments] < infile

where command is the name of the utility and infile is the file to be read. If the file does not exist, the command will produce an error.

The "redirect output" symbol (>) instructs the shell to write a program's output to a file instead of the terminal. The usage is

% command [options] [arguments] > outfile

If the outfile already exists, the shell will destroy its original contents.

Output from a command can be appended to a file rather than overwriting it by using the "append output" symbol (>>). The command line

% command [options] [arguments] >> outfile

appends the output of command to the file outfile.

This example creates a listing of the files in /usr/ucb in the file ucb.list, then displays the file:

% ls -al /usr/ucb > ucb.list

% cat ucb.list


  total 2277

 drwxr-xr-x   2 uservice  root        1312 Feb  7 08:25 .

 drwxr-xr-x  22 uservice  root         736 Jan 24 14:00 ..

 -rwsr-sr-x   1 uservice  sys       166912 Feb  7 08:25 chsh

 -rwxr-xr-x   1 bin       bin       121512 Oct 25 10:18 clear

 -rwxr-xr-x   1 bin       bin       151144 Oct 25 10:18 ctags

 -rwxr-xr-x   1 bin       bin       180760 Oct 25 10:18 diff





Under the C shell, standard error output can be redirected separately from

standard error output  by typing the command in the form



% (command > outfile) >& errfile




The Bourne shell and Korn shell allow the user to redirect standard error

information to a file and separate it from standard output by typing the

command in the form



$ command > outfile  2> errfile




Pipes



Standard output from one utility can be provided as standard input to

another utility by using a pipe (|). The usage is



% command1 | command2



where the output from command1 is used as input for

command2.  This example first requests the list of users logged

in to the system, then requests it again and pipes it through the sort

utility to provide an alphabetical listing:




 $ who

 operator   console      Oct 11 07:45

 ciosl      ttyp001      Oct 12 14:03   (scri1.scri.fsu.edu)

 jaya       ttyp003      Oct 13 07:37   (vsserv.scri.fsu.edu)

 holder     ttyp005      Oct 13 10:59   (croc.cc.fsu.edu)

 pjens      ttyp007      Oct 11 08:42   (systems.cc.fsu.edu)



 $ who|sort

 ciosl      ttyp001      Oct 12 14:03   (scri1.scri.fsu.edu)

 holder     ttyp005      Oct 13 10:59   (ssgcc.cc.fsu.edu)

 jaya       ttyp003      Oct 13 07:37   (vsserv.scri.fsu.edu)

 operator   console      Oct 11 07:45

 pjens      ttyp007      Oct 11 08:42   (systems.cc.fsu.edu)

 

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