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 <control-D> %
<control-D> 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 <control-D> %
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.
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 mycommandNow 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.
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.
% cp foo foo.2This 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.
% date Fri Jan 6 08:52:42 MST 1995
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
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 barThe file foo was transferred in binary mode, the file bar was transferred in ascii mode.
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 negroThen 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: 431-0987The 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
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.001This displays the first 20 lines of the file.
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.
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.
% mkdir essaysTo get "into" this directory, do
% cd essaysTo see what files are in essays, do this:
There shouldn't be any files there yet, since you just made it. To create files, see cat or emacs.
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:
For still more information, use the command man more.
Use this command to change the name of file and directories.
% mv foo foobar
The file that was named foo is now named foobar
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.
% 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 foo jwb321 % print notes.ps jwb321 % print manuscript.dvi jwb321To change the default printer, do this:
% setenv PRINTER jwb321
% 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.
% 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.
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.
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
% echo $PRINTER labprinter % setenv PRINTER myprinter % echo $PRINTER myprinter
red rojo green verde blue azul white blanco black negroThen we can do this:
% sort dict black negro blue azul green verde red rojo white blancoHere the output of sort went to the screen. To store the output in file we do this:
% sort dict >dict.sortedYou can check the contents of the file dict.sorted using cat , more , or emacs .
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.001This displays the last 20 lines of the file.
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.gzextracts the files.
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.
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 negroThen 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