UNIX Commands
A Brief Look
at Common
UNIX Commands
Lect. 3A
1
Using Unix System Commands
Most Unix commands use several options. Generally, your command
line will start with the name of the command, followed by the option or
options you want to use, followed by the arguments or arguments, if any.
Options are usually specified with a - ( minus sign.)
For example:
ls -l memo
Is the ls command with the -l option, and with memo as its sole argument.
This causes information about the file memo in your current directory, if it
exists, to be listed in long form.
ls -l
Is the ls command with -l option. It causes files in your current directory to
be listed in long form.
ls memo
Is the ls command with no options, and the argument memo. This command
will print the name of the file memo if it exists in the current directory.
Lect. 3A
2
Finding online Manual information by
Keyword ( man )
Command: man “command / topic”
- displays the
default
manual
entry for the
topic or
command.
Examples:
Use
capital
-K for
Linux
machines
Lect. 3A
$ man date
- display the “date” manual
page
$ man -k mount
- list all commands that have
the string “mount” in their
discriptions
$ man 1m mount
- display the “mount” manual
page section 1m.
$ man 3m mount
- display the “mount” manual
page section 3m.
At the bottom of the manual pages one will find
related files which often aid the user in finding more
information about a particular topic.
3
The Unix File System Hierarchy
“root”
/
bin
usr
ls
bin
man
man
tmp
contrib
bin
bin
vi
stand
kuss
local
pine
Lect. 3A
dev
passwd
mv
mail
etc
users
user1
user2
tmp
= directory
= file
4
The dot (.) and dot dot (..) directories
When any directory is created, two entries are automatically created
called dot (.) and dot dot (..) These are commonly used when designating
relative pathnames. By using the .. one can traverse up through the
hierarchy.
Dot (.)
The entry called dot represents your current directory position.
If you are currently in the directory: /users/user3:
.
represents the curent directory /users/user3
./file.dat
represents the file: /users/user3/file.dat
./memo/file.dat
represents the file: /users/user3/memo/file.dat
Dot Dot (..)
The entry called dot dot represents the directory immediately above your
current directory position, often refered to as the parent directory.
Lect. 3A
If you are currently in the directory: /users
..
represents the / directory
../..
also represents the / directory
../tmp
represents /tmp directory
../tmp/file.dat
represents /tmp/file.dat file
5
Path Names
Absolute Pathname
- Gives the complete designation of the location of a file or directory.
- Always starts at the top of the hierarchy ( the root “ / “ )
- Not dependent on your current location in the hierarchy.
- Always is unique across the entire hierarchy.
Eamples of files called numbers.dat
/tmp/numbers.dat
/users/user1/data/numbers.dat
/users/user2/numbers.dat
/users/user3/memos/numbers.dat
Relative Pathname
- Always starts at your current location in the hierarchy.
- Never starts with a / unless you are sitting in the root directory
- Is unique relative to your current locations only.
- Is often shorter than the absolute pathname.
Examples that again reference the files numbers.dat but assuming the
current position is the directory:
/users
Lect. 3A
user1/data/numbers.dat
user2/numbers.dat
6
Display your current working directory ( pwd )
Command:
pwd
Example:
login: user3
password: ******
Welcome to machine mpd306
$ pwd
/users/user3
$ cd ../user4
$ pwd
/users/user4
The pwd command reports the absolute pathname to your current
directory location in a UNIX systems file system, and is a shorthand
notation for Present Working Directory. This command is very useful when
you are traversing the directory structure and want to know where you
presently stand.
Lect. 3A
7
Methods to List the Contents of a Directory ( ls )
Command:
ls [ -adlFR ] [ directory_name ]
The ls command is used to List the names of files and directories.
With no arguments, ls displays the names of the files and directories under
the current directory. ls will accept arguments designating a relative or
absolute pathname of a file or directory. The command: ls -l is often used
to display the owner, group, and mode of the file or directory. The HP-Ux
Equivalent of the file is the command: ll
If the directory is too long to display on one screen this command is
often “piped” to a second UNIX command called: more. The total
command would be typed like this: ls -l | more
The ls command supports many options. Multiple options may be
supplied on a single command line to display more complete file or
directory information:
Lect. 3A
-a
Lists all files including those whose names start with a dot (.)
Normally these dot files are “hidden” except when the -a options is
specified. These dot files commonly hold configuration
information for your user session or applications.
-l
Provides a long listing which describes attributes about each file,
including: type, mode, number of links, owner, group, size (in
bytes), the modification date, and the name.
8
Permissions Displayed with ls -l
mode
- rw- r-- r-- 1 user3 class 37
- rwx r-x r-x 1 user3 class 37
d rwxr-x r-x 2 user3 class 1024
owner
type
owner
access
world
access
group
access
Lect. 3A
Jul 24 11:06
Jul 24 11:07
Jul 24 11:09
group
file1
file2
docs
file name
Size (bytes)
Last edit time
Number of links to this file.
9
Display Contents of Files ( cat / more / head / tail )
Command:
cat [ filename ......]
The cat command will concatenate and display the contents of file(s).
If the file is too big for the terminal’s screen, the text will go by too quickly
to read. A pipe can be used to direct the output of one command to the
input of another command. The more command is used to scroll the text to
the screen one page at a time. The following command is used: cat
filename | more
If a file contains control characters, such as a compiled program, and
you cat it to your terminal, your terminal may become disabled.
Command:
more [ filename ..... ]
The more command prints out the contents of the named files to the
screen one page at a time. To see the next screen of text you press the space
bar. To see only the next line you press the return key. To quit from the
command, use the q key.
Command: tail [-n] [filename]
The tail command is used to display the last n lines of a file. The
default is 10 lines if it is not specified. This command is useful if you only
want to see the last few lines in the file, and don’t want to scroll through the
entire file with the cat or more commands.
Lect. 3A
10
Change From one Directory to Another
Command:
(cd)
cd [ dir_pathname ]
The cd command allows you to change directory, and move to some
other location in the hierarchy. The path can be specified as an absolute or
relative pathname. When executed with no arguments, the cd command will
return you to you login or HOME directory. The command is used if a user
is lost within the UNIX directory structure and wishes to return to the
HOME directory. The pwd command is used to tell where one is presently
located.
Example:
$pwd
/users/user3
$cd memo; pwd
/users/user3/memo
$cd ../..; pwd
/users
cd /tmp; pwd
/tmp
Lect. 3A
11
Create or Remove Directories ( mkdir / rmdir )
Command: mkdir [ -p ] dir_pathname
rmdir dir_pathname
The mkdir command allows you to make a directory. When each
directory is created, it is automatically given the two sub-directories: dot (.)
and dot dot (..), representing the current and parent directories. Note:
creating the directories does not change your location in the hierarchy.
By default, when specifying a relative or absolute path to the directory
being created, all intermediate directories must exist. Alternatively, you can
use the option:
-p
Creates intermediate directories if they do not already exist.
Example: the following command would make the fruit directory if it did
not already exist:
$ mkdir -p fruit/apple fruit/grape fruit/orange
Lect. 3A
12
Remove Files ( rm )
Command: rm [ -if ] filename [ filenames ......]
individual files
Removes
The rm command is used to remove files. The files are irretrievable
once they are removed. The command will take many arguments, file
names or directory names. The following are options:
-i
Interrogate or interactive mode which requires that the user confirm
that the removal be completed. One responds with “y” or “n”.
Entering return is the same as no. This is often useful when a file has
been created with binary control characters and is difficult to remove.
rm -i *filename*
Example:
Lect. 3A
$ ls -F
file1 file2 documents/ memo/
$ rm file1
$ ls -F
file2 documents/ memo/
$ rm -i file2
file2 ? y
$ rm -i documents
rm: documents directory
13