UNIX Commands

ls ------ list files and directories
ls -a ------ list all files and directories
mkdir ------ make a directory
cd directory ------ change to named directory
cd ------ change to home-directory
cd ~ ------ change to home-directory
cd .. ------ change to parent directory
pwd ------ display the path of the current directory
cp file1 file2 ------ copy file1 and call it file2
mv file1 file2 ------ move or rename file1 to file2
rm file ------ remove a file
rmdir directory ------ remove a directory
cat file ------ display a file
less file ------ display a file a page at a time
head file ------ display the first few lines of a file
tail file ------ display the last few lines of a file
grep 'keyword' file ------ search a file for keywords
wc file ------ count number of lines/words/characters in file
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cat
This is one of the most flexible Unix commands. We can use to create, view and concatenate files. For our first example we create a three-item English-Spanish dictionary in a file called "dict."

% cat >dict
red rojo
green verde
blue azul

%

stands for "hold the control key down, then tap 'd'". The symbol > tells the computer that what is typed is to be put into the file dict. To view a file we use cat in a different way:

% cat dict
red rojo
green verde
blue azul
%

If we wish to add text to an existing file we do this:
% cat >>dict
white blanco
black negro

%

Now suppose that we have another file tmp that looks like this:

% cat tmp
cat gato
dog perro
%

Then we can join dict and tmp like this:
% cat dict tmp >dict2

We could check the number of lines in the new file like this:

% wc -l dict2
8

The command wc counts things --- the number of characters, words, and line in a file.


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chmod
This command is used to change the permissions of a file or directory. For example to make a file essay.001 readable by everyone, we do this:

% chmod a+r essay.001

To make a file, e.g., a shell script mycommand executable, we do this

% chmod +x mycommand

Now we can run mycommand as a command.
To check the permissions of a file, use ls -l . For more information on chmod, use man chmod.


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cd
Use cd to change directory. Use pwd to see what directory you are in.

% cd english
% pwd
% /u/ma/jeremy/english
% ls
novel poems
% cd novel
% pwd
% /u/ma/jeremy/english/novel
% ls
ch1 ch2 ch3 journal scrapbook
% cd ..
% pwd
% /u/ma/jeremy/english
% cd poems
% cd
% /u/ma/jeremy

Jeremy began in his home directory, then went to his english subdirectory. He listed this directory using ls , found that it contained two entries, both of which happen to be diretories. He cd'd to the diretory novel, and found that he had gotten only as far as chapter 3 in his writing. Then he used cd .. to jump back one level. If had wanted to jump back one level, then go to poems he could have said cd ../poems. Finally he used cd with no argument to jump back to his home directory.


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cp
Use cp to copy files or directories.
% cp foo foo.2

This makes a copy of the file foo.
% cp ~/poems/jabber .

This copies the file jabber in the directory poems to the current directory. The symbol "." stands for the current directory. The symbol "~" stands for the home directory.


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date
Use this command to check the date and time.
% date
Fri Jan 6 08:52:42 MST 1995


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echo
The echo command echoes its arguments. Here are some examples:

% echo this
this
% echo $EDITOR
/usr/local/bin/emacs
% echo $PRINTER
b129lab1

Things like PRINTER are so-called environment variables. This one stores the name of the default printer --- the one that print jobs will go to unless you take some action to change things. The dollar sign before an environment variable is needed to get the value in the variable. Try the following to verify this:

% echo PRINTER
PRINTER



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ftp
Use ftp to connect to a remote machine, then upload or download files. See also: ncftp

Example 1: We'll connect to the machine fubar.net, then change director to mystuff, then download the file homework11:

% ftp solitude
Connected to fubar.net.
220 fubar.net FTP server (Version wu-2.4(11) Mon Apr 18 17:26:33 MDT 1994) ready.
Name (solitude:carlson): jeremy
331 Password required for jeremy.
Password:
230 User jeremy logged in.
ftp> cd mystuff
250 CWD command successful.
ftp> get homework11
ftp> quit

Example 2: We'll connect to the machine fubar.net, then change director to mystuff, then upload the file collected-letters:

% ftp solitude
Connected to fubar.net.
220 fubar.net FTP server (Version wu-2.4(11) Mon Apr 18 17:26:33 MDT 1994) ready.
Name (solitude:carlson): jeremy
331 Password required for jeremy.
Password:
230 User jeremy logged in.
ftp> cd mystuff
250 CWD command successful.
ftp> put collected-letters
ftp> quit

The ftp program sends files in ascii (text) format unless you specify binary mode:

ftp> binary
ftp> put foo
ftp> ascii
ftp> get bar

The file foo was transferred in binary mode, the file bar was transferred in ascii mode.


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grep
Use this command to search for information in a file or files. For example, suppose that we have a file dict whose contents are

red rojo
green verde
blue azul
white blanco
black negro

Then we can look up items in our file like this;
% grep red dict
red rojo
% grep blanco dict
white blanco
% grep brown dict
%

Notice that no output was returned by grep brown. This is because "brown" is not in our dictionary file.

Grep can also be combined with other commands. For example, if one had a file of phone numbers named "ph", one entry per line, then the following command would give an alphabetical list of all persons whose name contains the string "Fred".

% grep Fred ph | sort
Alpha, Fred: 333-6565
Beta, Freddie: 656-0099
Frederickson, Molly: 444-0981
Gamma, Fred-George: 111-7676
Zeta, Frederick: 431-0987

The symbol "|" is called "pipe." It pipes the output of the grep command into the input of the sort command.
For more information on grep, consult

% man grep


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head
Use this command to look at the head of a file. For example,

% head essay.001

displays the first 10 lines of the file essay.001 To see a specific number of lines, do this:

% head -n 20 essay.001

This displays the first 20 lines of the file.
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ls
Use ls to see what files you have. Your files are kept in something called a directory.

% ls
foo letter2
foobar letter3
letter1 maple-assignment1
%

Note that you have six files. There are some useful variants of the ls command:

% ls l*
letter1 letter2 letter3
%

Note what happened: all the files whose name begins with "l" are listed. The asterisk (*) is the " wildcard" character. It matches any string.


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lpr
This is the standard Unix command for printing a file. It stands for the ancient "line printer." See

% man lpr

for information on how it works. See print for information on our local intelligent print command.


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mkdir
Use this command to create a directory.
% mkdir essays

To get "into" this directory, do
% cd essays

To see what files are in essays, do this:
% ls

There shouldn't be any files there yet, since you just made it. To create files, see cat or emacs.


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more
More is a command used to read text files. For example, we could do this:

% more poems

The effect of this to let you read the file "poems ". It probably will not fit in one screen, so you need to know how to "turn pages". Here are the basic commands:

q --- quit more
spacebar --- read next page
return key --- read next line
b --- go back one page
For still more information, use the command man more.



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mv
Use this command to change the name of file and directories.

% mv foo foobar

The file that was named foo is now named foobar



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ncftp
Use ncftp for anonymous ftp --- that means you don't have to have a password.

% ncftp ftp.fubar.net
Connected to ftp.fubar.net
> get jokes.txt

The file jokes.txt is downloaded from the machine ftp.fubar.net.



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print
This is a moderately intelligent print command.
% print foo
% print notes.ps
% print manuscript.dvi

In each case print does the right thing, regardless of whether the file is a text file (like foo ), a postcript file (like notes.ps, or a dvi file (like manuscript.dvi. In these examples the file is printed on the default printer. To see what this is, do

% print

and read the message displayed. To print on a specific printer, do this:
% print foo jwb321
% print notes.ps jwb321
% print manuscript.dvi jwb321

To change the default printer, do this:
% setenv PRINTER jwb321


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pwd
Use this command to find out what directory you are working in.
% pwd
/u/ma/jeremy
% cd homework
% pwd
/u/ma/jeremy/homework
% ls
assign-1 assign-2 assign-3
% cd
% pwd
/u/ma/jeremy
%

Jeremy began by working in his "home" directory. Then he cd 'd into his homework subdirectory. Cd means " change directory". He used pwd to check to make sure he was in the right place, then used ls to see if all his homework files were there. (They were). Then he cd'd back to his home directory.


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rm
Use rm to remove files from your directory.
% rm foo
remove foo? y
% rm letter*
remove letter1? y
remove letter2? y
remove letter3? n
%

The first command removed a single file. The second command was intended to remove all files beginning with the string "letter." However, our user (Jeremy?) decided not to remove letter3.


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rmdir
Use this command to remove a directory. For example, to remove a directory called "essays", do this:

% rmdir essays

A directory must be empty before it can be removed. To empty a directory, use rm.


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rsh
Use this command if you want to work on a computer different from the one you are currently working on. One reason to do this is that the remote machine might be faster. For example, the command

% rsh solitude

connects you to the machine solitude. This is one of our public workstations and is fairly fast.

See also: telnet


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setenv
% echo $PRINTER
labprinter
% setenv PRINTER myprinter
% echo $PRINTER
myprinter


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sort
Use this commmand to sort a file. For example, suppose we have a file dict with contents
red rojo
green verde
blue azul
white blanco
black negro

Then we can do this:
% sort dict
black negro
blue azul
green verde
red rojo
white blanco

Here the output of sort went to the screen. To store the output in file we do this:
% sort dict >dict.sorted

You can check the contents of the file dict.sorted using cat , more , or emacs .
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tail
Use this command to look at the tail of a file. For example,

% tail essay.001

displays the last 10 lines of the file essay.001 To see a specific number of lines, do this:

% tail -n 20 essay.001

This displays the last 20 lines of the file.
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tar
Use create compressed archives of directories and files, and also to extract directories and files from an archive. Example:

% tar -tvzf foo.tar.gz

displays the file names in the compressed archive foo.tar.gz while

% tar -xvzf foo.tar.gz

extracts the files.
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telnet
Use this command to log in to another machine from the machine you are currently working on. For example, to log in to the machine "solitude", do this:

% telnet solitude

See also: rsh.


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wc
Use this command to count the number of characters, words, and lines in a file. Suppose, for example, that we have a file dict with contents

red rojo
green verde
blue azul
white blanco
black negro

Then we can do this
% wc dict
5 10 56 tmp

This shows that dict has 5 lines, 10 words, and 56 characters.

The word count command has several options, as illustrated below:

% wc -l dict
5 tmp
% wc -w dict
10 tmp
% wc -c dict
56 tmp
===============================================================

Access Control

exit - terminate a shell (see "man sh" or "man csh")
logout - sign off; end session (C shell and bash shell only; no man page)
passwd - change login password
rlogin - log in remotely to another UNIX system
slogin - secure version of rlogin

Communications

from - list senders of mail
Mail - send and receive mail
mesg - permit or deny terminal messages and talk requests
pine - send and receive mail (easiest for new users)
talk - talk to another logged-in user (full screen)
write - write to another logged-in user

Programming Tools

ar - archive and library maintainer
as - assembler, specific to each machine architecture
awk - pattern scanning and processing language
/bin/time - time a command
cc - C compiler
crontab - maintain periodic tasks
csh - C shell command interpreter
dbx - source-level debugging program
gdb - GNU Project debugger
gprof - display profile of called routines
kill - kill a process
ld - the UNIX loader
lex - generate lexical analysis programs
lint - check C source code
make - maintain large programs
maple - symbolic mathematics program
nice - run a command at low priority (see "man nice" or "man csh")
nohup - run a command immune to hangups
pc - Pascal compiler (xlp on ADS)
perl - Popular script interpreter
prof - display profile data
ranlib - convert archives to random libraries
sh - Bourne shell command interpreter
yacc - generate input parsing programs

Documentation

apropos - locate commands by keyword lookup
info - start the InfoExplorer program
man - find manual information about commands
/usr/bin/X11/dxbook - start the BookReader program
whatis - describe what a command is
whereis - locate source, binary, or man page for a program

Editors

ed - line-oriented text editor
emacs - screen-oriented text editor
ex - line-oriented text editor
pico - simple, screen-oriented text editor (easiest for new users)
sed - stream-oriented text editor
vi - full-screen text editor
vim - full-screen text editor ("vi-improved")

File and Directory Management

cd - change working directory
chmod - change the protection of a file or directory
cmp - compare two files
comm - select/reject lines common to two sorted files
compress - compress a file
cp - copy files
crypt - encrypt/decrypt files
diff - compare the contents of two ASCII files
file - determine file type
grep - search a file for a pattern
ln - make a link to a file
ls - list the contents of a directory
mkdir - create a directory
mv - move or rename files and directories
pwd - show the full pathname of your working directory
quota - display disk usage and limits
rm - delete (remove) files
rmdir - delete (remove) directories
sort - sort or merge files
tee - copy input to standard output and other files
tr - translate characters
umask - change default file protections
uncompress - restore compressed file
uniq - report (or delete) repeated lines in a file
wc - count lines, words, and characters in a file

File Display and Printing

cat - show the contents of a file; catenate files
fold - fold long lines to fit output device
head - show first few lines of a file
lpq - examine the printer spooling queue
lpr - print a file
lprm - remove jobs from the printer spooling queue
more - display a file, one screen at a time
page - like "more", but prints screens top to bottom
pr - paginate a file for printing
tail - show the last part of a file
zcat - display a compressed file

File Transfer

ftp - transfer files between network hosts
rcp - transfer files between networked UNIX hosts
scp - secure version of rcp
rz - receive files using ZMODEM protocol
sz - send files using ZMODEM protocol

Miscellaneous

alias - define synonym commands
chsh - change default login shell
clear - clear terminal screen
echo - echo arguments
pbm - portable bitmap manipulation programs
popd - pop the directory stack (C shell only)
pushd - push directory on stack (C shell only)
script - make typescript of terminal session
setenv - set an environment variable (C shell only)
stty - set terminal options

News/Networks

netstat - show network status
Pnews - submit USENET news articles
rlogin - login remotely on another UNIX system
slogin - secure version of rlogin
tin - read/post USENET news articles
trn - read/post USENET news articles using threaded news reader
rsh - run shell or command on another UNIX system
ssh - secure-shell version of rsh
telnet - run Telnet to log in to remote host

Process Control

(The following commands function under the C shell, bash, and ksh. They do not have separate man pages.)

bg - put suspended process into background
fg - bring process into foreground
jobs - list processes
^y - suspend process at next input request
^z - suspend current process

Status Information

date - show date and time
df - summarize free disk space
du - summarize disk space used
env - display environment
finger - look up user information
history - list previously issued commands (C shell, bash, and ksh
only)
last - indicate last login of users
lpq - examine spool queue
manpath - show search path for man pages
printenv - print out environment
ps - show process status
pwd - print full pathname of working directory
set - set shell variables (C shell, bash, and ksh only)
stty - set terminal options
uptime - show system load, how long system has been up
w - show who is on system, what command each job is executing
who - show who is logged onto the system
whois - Internet user name directory service

Text Processing

addbib - create or extend bibliographic database
checknr - check nroff/troff files
col - filter reverse line feeds
diction - identify wordy sentences
diffmk - mark differences between files
dvips - convert TeX DVI files into PostScript
eqn - typeset mathematics with troff
explain - explain phrases found by diction program
grap - pic preprocessor for drawing graphs
hyphen - find hyphenated words
indxbib - build inverted index for a bibliography, find references
ispell - check spelling interactively
latex - format text
lookbib - find bibliography references
macref - make cross-reference listing of nroff/troff macro files
ndx - create a subject-page index for a document
neqn - format mathematics with nroff
nroff - format text for simple display
pic - make simple pictures for troff input
psdit - filter troff output for Apple LaserWriter
ptx - make permuted index (not on CCWF)
refer - insert references from bibliographic databases
roffbib - run off bibliographic database
sortbib - sort bibliographic database
spell - find spelling errors
style - analyze surface characteristics of a document
tbl - format tables for nroff/troff
tex - format text
tpic - convert pic source files into TeX commands
troff - format text
=================================================

Shell Variables

Shell variables are used for storing and manipulating strings of characters. A shell variable name begins with a letter and can contain letters, digits, and underscores, such as
x
x1
abc_xyz

Shell variables can be assigned values like this:
x=file1
x1=/usr/man/man1/sh.1
abc_xyz=4759300

Notice that there are no spaces before or after the equals-sign. The value will be substituted for the shell variable name if the name is preceded by a $. For example,
echo $x1

would echo
/usr/man/man1/sh.1

Several special shell variables are predefined. Some useful ones are
$#, $*, $?, and $$.

Arguments can be passed to a shell script. These arguments can be accessed inside the script by using the shell variables $1, $2,...,$n for positional parameter 1,2,...,n. The filename of the shell script itself is $0. The number of such arguments is $#. For example, if file do_it is a shell script and it is called by giving the command
do_it xyz

then $0 has the value do_it, $1 has the value xyz, and $# has the value 1.
$* is a variable containing all the arguments (except for $0) and is often used for passing all the arguments to another program or script.

$? is the exit status of the program most recently executed in the shell script. Its value is 0 for successful completion. This variable is useful for error handling (see section 10.6).

$$ is the process id of the executing shell and is useful for creating unique filenames. For example,

cat $1 $2 >> tempfile.$$

concatenates the files passed as parameters 1 and 2, appending them to a file called tempfile.31264 (assuming the process id is 31264).
Flow Control
Most programming languages provide constructs for looping and for testing conditions to know when to stop looping. The shell provides several such flow control constructs, including if, for, and while.
if

The if command performs a conditional branch. It takes the form

if command-list1
then
command-list2
else
command-list3
fi

A command-list is one or more commands. You can put more than one command on a line, but if you do so, separate them by semicolons. If the last command of command-list1 has exit status 0, then command-list2 is executed. But if the exit status is nonzero, then command-list3 is executed.
for

The for command provides a looping construct of the form

for shell-variable in word-list
do command-list
done

The shell variable is set to the first word in word-list and then command-list is executed. The shell variable is then set to the next word in word-list and the process continues until word-list is exhausted. A common use of for-loops is to perform several commands on all (or a subset) of the files in your directory. For example, to print all the files in your directory, you could use
for i in *
do echo printing file $i
lpr $i
done

In this case, * would expand to a list of all filenames in your directory, i would be set to each filename in turn, and $i would then substitute the filename for i (in the echo and lpr commands).
while

The while command provides a slightly different looping construct:

while command-list1
do command-list2
done

While the exit status of the last command in command-list1 is 0, command-list2 is executed.
Test
The test command can be used to compare two integers, to test if a file exists or is readable, to determine if two strings are equal, or to test several other conditions. For example, to test whether the value of shell variable x is equal to 5, use
test $x -eq 5

If $x is equal to 5, test returns true.
Other useful tests include

test -s file (true if file exists and has a size larger than 0)
test -w file (true if file exists and is writable)
test -z string (true if the length of string is 0)
test string1 != string2
(true if string1 and string2 are not identical)

The test command is often used with the flow-control constructs described above. Here is an example of test used with the if command:
if test "$1" = "" (or if ["$1" = ""] )
then
echo usage: myname xxxx
exit 1
fi

This tests to see if the command line contains an argument ($1). If it does not ($1 is null), then echo prints a message.
A complete list of test operators can be found in the man page for test.

Error Handling

Each time a program is executed from within a shell script, a value is returned to indicate whether the program ran successfully or not. In most cases, a value of zero is returned on successful execution, and a nonzero number is returned if the program encountered an error. This exit status is available in the shell variable $?.
For example,

grep $1 phonelist
if test $? -ne 0
then
echo I have no phone number for $1
fi

will run a program (grep) and examine the exit status to determine if the program ran properly.
Traps
Some signals cause shell scripts to terminate. The most common one is the interrupt signal ^c typed while a script is running. Sometimes a shell script will need to do some cleanup, such as deleting temporary files, before exiting. The trap command can be used either to ignore signals or to catch them to perform special processing. For example, to delete all files called ``tmp.*'' before quitting when an interrupt signal is generated, use the command
trap 'rm tmp.*; exit' 2

The interrupt signal is signal 2, and two commands will be executed when an interrupt is received (rm tmp.* and exit). You can make a shell script continue to run after logout by having it ignore the hangup signal (signal 1). The command
trap ' ' 1

allows shell procedures to continue after a hangup (logout) signal.
Command Substitution
A useful capability in shell programming is to assign the output from a program to a shell variable or use it as a pattern in another command. This is done by enclosing the program call between accent grave (`) characters. For example, the command
where=`pwd`

will assign the string describing the current working directory (the results of the pwd command) to the shell variable where. Here is a more complicated example:
for i in `ls -t *.f`
do f77 $i
a.out >output
cat $i output | lpr -P$1
rm a.out output
done

In this case, the shell script executes a series of commands for each file that ends with ``.f'' (all Fortran programs). The `ls -t *.f` is executed and expands into all filenames ending with ``.f'', sorted by time, most recent to oldest. Each is compiled and executed. Then the source file and output file are sent to the printer identified by the first argument ($1) passed to the shell script. Then these files are deleted.
I/O Redirection
Besides the I/O redirection already described, there are a few additional forms of redirection. Under the Bourne shell, standard input is also associated with file descriptor 0, standard output with file descriptor 1, and standard error output with file descriptor 2. So both >file and 1>file redirect standard output to file, and 2>file redirects standard error output to file.
To merge standard output (file descriptor 1) and standard error output (file descriptor 2), then redirect them to another file, use this notation:

command >file 2>&1

Another method of redirecting input in shell scripts allows a command to read its input from the shell script itself without using temporary files. For instance, to run the editor ed to change all x's in a file to z's, you could create a temporary file of ed commands, then read it to perform those commands, and finally delete it, like this:
echo "1,$s/x/z/g" >edtmp.$$
echo "w" >>edtmp.$$
echo "q" >>edtmp.$$
ed filename rm edtmp.$$
echo "x's changed to z's"

The same thing can be accomplished without a temporary file by using the << symbol and a unique string, like this:
ed filename <<%
1,$s/x/z/g
w
q
%
echo "x's changed to z's"

The << symbol redirects the standard input of the command to be right here in the shell script, beginning from the next line and continuing up to the line that matches the string following the << (in this case %). The terminating string must be on a line by itself. The string is arbitrary: for example, <Debugging Shell Scripts
Two methods of tracing shell script execution are useful for debugging. The script may be called with a verbose flag (-v) or execution trace flag (-x). The -v flag causes each line of the shell script to be echoed as it is read but after all substitutions are performed. The -x flag causes each line to be echoed just before it is executed. For example:
sh -v do_it
sh -x do_it

To turn on both flags, use -vx.