Introduction to Unix commands
Following is a very brief introduction to some useful Unix commands, including examples of how to use each command. For more extensive information about any of these commands, use the
man command as described below. Sources for more information appear at the end of this document.
On this page:
This command will print a calendar for a specified month and/or year.
To show this month's calendar, enter:
To show a twelve-month calendar for 2008, enter:
To show a calendar for just the month of June 1970, enter:
cal 6 1970
This command outputs the contents of a text file. You can use it to read brief files or to concatenate files together.
file1 onto the end of
cat file1 >> file2
To view the contents of a file named
cat displays text without pausing, its output may quickly scroll off your screen. Use the
less command (described below) or an editor for reading longer text files.
This command changes your current directory location. By default, your Unix login session begins in your home directory.
To switch to a subdirectory (of the current directory) named
To switch to a directory named
To move to the parent directory of the current directory, enter:
To move to the root directory, enter:
To return to your home directory, enter:
This command changes the permission information associated with a file. Every file (including directories, which Unix treats as files) on a Unix system is stored with records indicating who has permission to read, write, or execute the file, abbreviated as r, w, and x. These permissions are broken down for three categories of user: first, the owner of the file; second, a group with which both the user and the file may be associated; and third, all other users. These categories are abbreviated as u for owner (or user), g for group, and o for other.
To allow yourself to execute a file that you own named
chmod u+x myfile
To allow anyone who has access to the directory in which
myfile is stored to read or execute
chmod o+rx myfile
You can view the permission settings of a file using the
ls command, described below.
Note: Be careful with the
chmod command. If you tamper with the directory permissions of your home directory, for example, you could lock yourself out or allow others unrestricted access to your account and its contents.
For more, see In Unix, how do I change the permissions for a file?
This command copies a file, preserving the original and creating an identical copy. If you already have a file with the new name,
cp will overwrite and destroy the duplicate. For this reason, it's safest to always add
-i after the
cp command, to force the system to ask for your approval before it destroys any files. The general syntax for
cp -i oldfile newfile
To copy a file named
meeting1 in the directory
/home/dvader/notes to your current directory, enter:
cp -i /home/dvader/notes/meeting1 .
. (period) indicates the current directory as destination, and the
-i ensures that if there is another file named
meeting1 in the current directory, you will not overwrite it by accident.
To copy a file named
oldfile in the current directory to the new name
newfile in the
mystuff subdirectory of your home directory, enter:
cp -i oldfile ~/mystuff/newfile
~ character (tilde) is interpreted as the path of your home directory.
Note: You must have permission to read a file in order to copy it.
date command displays the current day, date, time, and year.
To see this information, enter:
This command reports file system disk usage (i.e., the amount of space taken up on mounted file systems). For each mounted file system,
df reports the file system device, the number of blocks used, the number of blocks available, and the directory where the file system is mounted.
To find out how much disk space is used on each file system, enter the following command:
df command is not configured to show blocks in kilobytes by default, you can issue the following command:
This command reports disk usage (i.e., the amount of space taken up by a group of files). The
du command descends all subdirectories from the directory in which you enter the command, reporting the size of their contents, and finally reporting a total size for all the files it finds.
To find out how much disk space your files take up, switch to your home directory with the
cd command, and enter:
The numbers reported are the sizes of the files; on different systems, these sizes will be in units of either 512 byte blocks or kilobytes. To learn which is the case, use the
man command, described below. On most systems,
du -k will give sizes in kilobytes.
find command lists all of the files within a directory and its subdirectories that match a set of conditions. This command is most commonly used to find all of the files that have a certain name.
To find all of the files named
myfile.txt in your current directory and all of its subdirectories, enter:
find . -name myfile.txt -print
To look in your current directory and its subdirectories for all of the files that end in the extension
find . -name "*.txt" -print
In these examples, the
. (period) represents your current directory. It can be replaced by the full pathname of another directory to search. For instance, to search for files named
myfile.txt in the directory
/home/user/myusername and its subdirectories, enter:
find /home/user/myusername/ -name myfile.txt -print
On some systems, omitting the final
/ (slash) after the directory name can cause
find to fail to return any results.
As a shortcut for searching in your home directory, enter:
find "$HOME/" -name myfile.txt -print
This command reports any programs that you suspended and still have running or waiting in the background (if you had pressed
Ctrl-z to suspend an editing session, for example). For a list of suspended jobs, enter:
Each job will be listed with a number; to resume a job, enter
% (percent sign) followed by the number of the job. To restart job number two, for example, enter:
This command is only available in the
Use this command as a last resort to destroy any jobs or programs that you suspended and are unable to restart. Use the jobs command to see a list of suspended jobs. To kill suspended job number three, for example, enter:
Now check the
jobs command again. If the job has not been cancelled, harsher measures may be necessary. Enter:
kill -9 %3
less and more
more display the contents of a file one screen at a time, waiting for you to press the Spacebar between screens. This lets you read text without it scrolling quickly off your screen. The
less utility is generally more flexible and powerful than
more is available on all Unix systems while
less may not be.
To read the contents of a file named
textfile in the current directory, enter:
less utility is often used for reading the output of other commands. For example, to read the output of the
ls command one screen at a time, enter:
ls -la | less
In both examples, you could substitute
less with similar results. To exit either
q. To exit
less after viewing the file, press
Note: Do not use
more with executables (binary files), such as output files produced by compilers. Doing so will display garbage and may lock up your terminal.
lpr and lp
These commands print a file on a printer connected to the computer network. The
lpr command is used on BSD systems, and the
lp command is used in System
V. Both commands may be used on the UITS systems.
To print a file named
myfile on a printer named
lpr -Plp1 myfile
To print the same file to the same printer with
lp -dlp1 myfile
Note: Do not print to a printer whose name or location is unfamiliar to you.
This command will list the files stored in a directory. To see a brief, multi-column list of the files in the current directory, enter:
To also see "dot" files (configuration files that begin with a period, such as
To see the file permissions, owners, and sizes of all files, enter:
If the listing is long and scrolls off your screen before you can read it, combine
ls with the
less utility, for example:
ls -la | less
For more, see In Unix, how do I list the files in a directory?
This command displays the manual page for a particular command. If you are unsure how to use a command or want to find out all its options, you might want to try using
man to view the manual page.
For example, to learn more about the
ls command, enter:
To learn more about
If you are not sure of the exact command name, you can use
man with the
-k option to help you find the command you need. To see one line summaries of each reference page that contains the keyword you specify, enter:
man -k keyword
keyword in the above example with the keyword which you want to reference. Also see In Unix, what is the man command, and how do I use it to read manual pages?
This command will make a new subdirectory.
To create a subdirectory named
mystuff in the current directory, enter:
To create a subdirectory named
morestuff in the existing directory named
Note: To make a subdirectory in a particular directory, you must have permission to write to that directory.
This command will move a file. You can use
mv not only to change the directory location of a file, but also to rename files. Unlike the
mv will not preserve the original file.
Note: As with the
cp command, you should always use
-i to make sure you do not overwrite an existing file.
To rename a file named
oldname in the current directory to the new name
mv -i oldname newname
To move a file named
hw1 from a subdirectory named
newhw to another subdirectory named
oldhw (both subdirectories of the current directory), enter:
mv -i newhw/hw1 oldhw
If, in this last operation, you also wanted to give the file a new name, such as
firsthw, you would enter:
mv -i newhw/hw1 oldhw/firsthw
ps command displays information about programs (i.e., processes) that are currently running. Entered without arguments, it lists basic information about interactive processes you own. However, it also has many options for determining what processes to display, as well as the amount of information about each. Like
lpr, the options available differ between BSD and System V implementations. For example, to view detailed information about all running processes, in a BSD system, you would use
ps with the following arguments:
To display similar information in System V, use the arguments:
For more information about
ps refer to the
man page on your system. Also see In Unix, what do the output fields of the ps command mean?
This command reports the current directory path. Enter the command by itself:
This command will remove (destroy) a file. You should enter this command with the
-i option, so that you'll be asked to confirm each file deletion. To remove a file named
rm -i junk
rm will remove a file permanently, so be sure you really want to delete a file before you use
To remove a non-empty subdirectory,
rm accepts the
-r option. On most systems this will prompt you to confirm the removal of each file. This behavior can be prevented by adding the
-f option. To remove an entire subdirectory named
oldstuff and all of its contents, enter:
rm -rf oldstuff
Note: Using this command will cause
rm to descend into each subdirectory within the specified subdirectory and remove all files without prompting you. Use this command with caution, as it is very easy to accidently delete important files. As a precaution, use the
ls command to list the files within the subdirectory you wish to remove. To browse through a subdirectory named
ls -R oldstuff | less
This command will remove a subdirectory. To remove a subdirectory named
Note: The directory you specify for removal must be empty. To clean it out, switch to the directory and use the
rm commands to inspect and delete files.
This command displays or changes various settings and options associated with your Unix session.
To see the status of all settings, enter the command without options:
If the output scrolls off your screen, combine
set | less
The syntax used for changing settings is different for the various kinds of Unix shells; see the
man entries for
set and the references listed at the end of this document for more information.
This command starts the vi text editor. To edit a file named
myfile in the current directory, enter:
The vi editor works fairly differently from other text editors. If you have not used it before, you should probably look at a tutorial, such as How do I use the vi text editor?
The very least you need to know to start using vi is that in order to enter text, you need to switch the program from command mode to insert mode by pressing
i. To navigate around the document with the cursor keys, you must switch back to command mode by pressing
Esc. To execute any of the following commands, you must switch from command mode to ex mode by pressing
: (the colon key): Enter
w to save;
wq to save and quit;
q! to quit without saving.
w and who
who commands are similar programs that list all users logged into the computer. If you use
w, you also get a list of what they are doing. If you use
who, you also get the IP numbers or computer names of the terminals they are using.
At Indiana University, for personal or departmental Linux or Unix systems support, see At IU, how do I get support for Linux or Unix?
This is document afsk in the Knowledge Base.
Last modified on 2016-12-06 11:14:03.
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