BASIC UNIX COMMANDS
COMMANDS
Commands are what you type at the prompt. Commands have
arguments on which they operate. For example, in rm temp,
the command is rm and the argument is temp; this
command removes the file called temp. Here I put arguments
in UPPER CASE. Thus, words such as FILE are taken to stand for
some other word, such as temp. In the following list, I
use [ ] for optional arguments that are not typicaly used.
Commands have options that are controlled with switches, which
are usually letters following a single dash. Usually you can
write several letters after one dash. For example ls -l
lists files in a long format, with more information. ls -a
lists all the files, including those that begin with ., which are
usually files used by various programs. ls -al lists all
the files in the long format. The following list omits most
options. Many programs will give you a list of their options if
you type the name of the program followed by -h or -?.
Other options are controlled in special files usually beginning
with ., such as .emacs, .mailrc, and .newsrc.
You can edit these. The file .cshrc contains general
options, plus aliases that you make up for commands you use often.
- , the pipe symbol, takes the output of one command and
gives it to the second command as input, for example, ls -l
- more allows you to view a long file list through "more".
> directs the output to a file, e.g., ls -l >
listing.tmp puts the listing into a file named listing.tmp. >
overwrites an old file of the same name. >> appends to a file.
* stands for any string of letters. For example, ls
t* lists all the files beginning with t.
recalls previous commands, and you can edit these
commands using emacs editing.
The tab key completes commands if you type the first few letters.
ctrl-z suspends most programs. fg resumes.
ctrl-c stops most programs.
alias abbreviates a series of commands, separated
by semicolons. Useful in .cshrc.
GETTING HELP
apropos KEYWORD: Looks for commands related to KEYWORD.
man COMMAND: Shows manual pages on COMMAND. This is
the authoritative source on the items described here. The
commands can do much more than is listed here.
whatis COMMAND: Tells what COMMAND does.
FILES AND DIRECTORIES
All information is stored in files. File names and commands are
case sensitive. Case matters. Files are contained in
directories. You start out in your own home directory, and your
prompt usually tells its name. At any given time, one of these
directories is your working directory, the one you are in.
You can refer to files in your working directory by just their
names. You can refer to a file that is in a subdirectory by
giving a subdirectory name, a slash, and the file name, e.g.,
Mail/baron. You can refer to any file on the computer by giving
its full name, starting with a slash, such as
/home7/b/baron/mbox.
If the file is a program, typing its name will run it. (That is
what commands do.) If the program is something you have just
written and is in the director you are in, put ./ before
the name. If the file is not a program, typing its name will give
you an error message. If you want to see its contents, for
example, you must use a command such as "more" before the file
name.
ls [DIRECTORY]: Lists files. (Also try: ls -f, ls -s, ls -a.)
rm FILE: Removes FILE.
more FILE or less FILE: View FILE. (? or h
for help.)
cd DIRECTORY: Change the directory you are in to
DIRECTORY.
cd: Change to your home directory.
cd ..: Change to the next directory up in the hierarchy.
mkdir DIRECTORY: Make DIRECTORY.
rmdir DIRECTORY: Remove DIRECTORY.
rm -rf: Recursively remove a directory and anything in it.
mv FILE1 FILE2: Moves or renames FILE1 to FILE2.
cp FILE1 FILE2: Makes a copy of FILE1, called FILE2.
cat FILE1 FILE2 > FILE3: Concatenate FILE1 and
FILE2, calling the result FILE3.
chmod 644 FILE: Unprotect FILE for others to read or copy.
chmod 755 FILE: Unprotect program or "script."
chmod 755 DIRECTORY: Unprotect DIRECTORY, needed for web
page directories.
head and tail: Print the top and bottom of a
text file.
TEXT FILE MANIPULATION
These commands operate on files. The output goes to the
"standard output," which is your terminal display. If you want
to "redirect" the output to a file, use > FILENAME at
the end of the command (with FILENAME being the name of
the file). Use >> instead of > if you want to
append to the file rather than write it from scratch.
diff: Find the differences between two text files.
grep LETTER-STRING FILE1 [> FILE2]: Prints (or puts
in FILE2) all lines of FILE1 that contain LETTER-STRING. Use the
-v switch to get lines not containing the string.
sed s/STRING1/STRING2/g: replace STRING1 with
STRING2 throughout a file. See also the y
switch for replacing characters.
cut -d" " -f2 FILE: Extract the second column from a file,
where the columns are delimited by spaces. Use paste to
put such cuttings back together.
sort FILE: Sort the lines alphabetically.
uniq FILE: Remove adjacent duplicate lines. Typically
used with the output of sort, e.g., sort FILE - uniq.
Use the -c to count the number of adjacent examples of each
line.
wc FILE: Count characters, words, and lines.
WHAT'S GOING ON?
w [USER]: Who is using the computer. This is useful to see
whether you are logged on twice. (See ps and kill, below, in
case this happens.) Also try who and finger.
finger USER: Gives information about the user, including
the files .project and .plan, if you have these files. You can
sometimes use this for people on other computers.
You can keep useful information in your .plan, such as your
schedule, your phone number, etc.
quota -v: Tells you how much of your quota for files is
used up.
ps -fu USERNAME: Lists the processes that you are running,
if you put in your username. You can use this to
find the number of processes that you want to kill, such as those
left over when you did not log out properly. It is the
first number listed.
kill PROCESS-NUMBER: Kills the process you don't
want. If this doesn't work, try kill -9 PROCESS-NUMBER.
last -22: Shows you the last 22 users who logged in.
THE INTERNET
mutt and elm: Read and write electronic mail. Each
has its own "help". See the discussion of these in the
psychology web page computer section.
slrn and tin: Read news (and respond to postings).
Pnews: Post to newsgroups. (You can also say mutt
psych-general@psych or elm psych-general@psych to post to
upenn.psych.general.)
lynx [URL]: Reads web pages as text files.
ssh HOST: Connects to a remote computer.
talk USERNAME: Allows you to talk with someone logged
on. The full username must be specified for remote computers,
and you must use ntalk instead of talk. It is
not a good idea to use this casually unless you know that the
other person will not be annoyed.
TRANSFERRING FILES
Many computers on the internet have ftp or ssh, but all of the programs
for transferring files depend on having the relevant software on
both computers.
ftp and scp: Fast way of uploading and downloading, or moving any
file from one computer to another. For example, scp
myfile baron@psych.upenn.edu: - you need the colon at the end.
rsync: synchronize files or directories on two different
computers. Good for backing up.
EDITING
pico FILE or emacs FILE xemacs FILE or
vi FILE: Edit FILE. One of these editors may be specified as
the default for mailing and news programs. Pico is easiest
because it has all the commands listed at the bottom of the
screen, but it is the least useful because it has few commands.
COMPRESSING, ENCRYPTING, and SECURITY
tar cvf FILE.tar and tar xvf FILE.tar: Create
and extract an archive file. Useful for backing up directories.
On Linux xvfz will extract and unzip in one step.
gzip FILE: Reduce the size of files for storage. use
gunzip FILE to unzip them. Files "zipped" with gzip have
the suffix .gz.
crypt < FILE1 > FILE2: Encrypts or decodes file1 so
that you need a password to read it. But if you want to be
absolutely sure beyond any doubt that nobody will read your
files, do not leave them on cattell.
antiword FILE1 > FILE2: Decodes a Word file into text.
(That is all most of them are.) Save storage space. You can use
this with Mutt or Elm to read doc files sent in email messages.
passwd: Change your password.
Jon Baron, September, 2003
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On 6 Sep 2005, 11:44.