Using Linux Commands

1
Using Linux Commands

• Lab 3

2
Using the Shell in LinuxCommands Syntax

• Options
• could be added to the commands to change their
  behavior (-a , -la , --help)
• Argument
• is an extra piece of information (ex. a file
  name)
• Environment variables
• where the shell stores information that may be
  useful to the users shell session.
• Examples of environment variables include SHELL
  (which identifies the shell you are using
  )andPS1 (which defines your shell prompt)
• Meta characters
• that have special meaning to the shell
• (gt) used to direct the output of a command to a
  file.
• ( ) pipe the output to another command.

3
Getting Help with Using the Shell

• Use --help with the command (date --help)
• Use the man command
• man manual
• To reading a manual and return to the shell
  prompt within the open terminal ? press q

4
Understanding file permission

• Why
• Keep users from accessing other users private
  files
• To protect important system files
• permissions bits
• rwx rwx rwx
• Owners Group Others
• r read w write x execute

ls al
-rw-rw-r-- 1 chris sales 1024 May 10 0149 .. drwxr-xr-x 2 chris sales 2204 May 18 2130 .bash_history
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Understanding file permission

• For Files
• "Read" means to be able to open and view the file
• "Write" means to overwrite or modify the file
• "eXecute" means to run the file as a binary
  files are executable only if they are programs
  and shell scripts, not useful for data files.
• For Directories
• "Read" means to be able to view the contents of
  the directory
• "Write" means to be able to create new
  files/directories or delete files/directories
  within the directory
• "eXecute" means to be able to "Change Directory"
  (cd) into the directory permission to access
  the directory.
• How to view the permission for a file or
  directory?
• ls -al

6
Understanding file permission
1 2 3 4 5 6 7 8 9 10
d directory - file
Permission for the group
Permission for the others
Permission for the owner

• if the permission field is - ? the permission
  is not given.

7
Understanding file permission

• Only the owner of a file can change its
  permission.
• How to set file permission?
• Use the command chmod(change file mode bits).
• chmod has two notations
• Numeric(octal) notation.
• Symbolic notation.

8
Change permission on a file - numeric

• the file permissions aren't represented by
  characters. Instead, they are represented by a
  three-digit octal number.
• 4 read (r)2 write (w)1 execute (x)0 no
  permission (-)

Octal (421) Binary permission
0 000 000 ---
1 001 001 --x
2 020 010 -w-
3 021 011 -wx
4 400 100 r--
5 401 101 r-x
6 420 110 rw-
7 421 111 rwx
725
If the permission is
421
020
401
rwx
-w-
r-x
9
Change permission on a file symbolic

• Permissions are represented by characters rwx
• This gives who the specified permissions for a
  given filename.
• The who is a list of letters re going to be
  giving permissions to. These may be specified in
  any order.
• ? add the selected permission.
• - ? remove the selected permission.

chmod who permission filename
chmod who - permission filename
u The user who owns the file (this means you.)
g The group the file belongs to.
o The other users not in the files group.
a all of the above (an abbreviation for ugo)
10
Change permission on a file

• For r, w, x octal value is 4,2,1 respectively

chmod 777 file-name ? rwxrwxrwx chmod 755 file-name ? rwxr-xr-x

• owner(u) group(g) other(o) all(a)
  rwxrwxrwx

chmod a-w file-name ? r-xr-xr-x chmod go-rwx file-name ? rwx------

• owner(u) group(g) other(o) all(a)
  ---------

chmod urw file-name ? rw-------
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Creating files and directories

• Use the command mkdir to create a new directory
  to the current working directory.
• mkdir directoryName

12
Creating files and directories

• Go to your home directory. Type cd.
• Make sure that you got to your home directory,
  type pwd
• Create a new directory called test in your home
  directory
• Check the permissions of the directory by typing
• Suppose that you want to prevent everyone else
  from using or viewing the files in this
  directory
• Make the test directory your current directory

mkdir test
ls ld test
drwxr-xr-x 2 chris sales 1024 May 18 2130 test
chmod 700 test
cd test
13
Creating files and directories

• To create a directory(test) in the Desktop, we
  have two ways
• mkdir /home/chris/Desktop/test
• cd /home/chris/Desktopmkdir test
• NOTE
• The -d option tells ls not to list the contents
  of the test directory just show us the listing
  for the directory itself.

ls ld test provide a long listing of the test directory, without showing the contents of the test directory.
14
Moving, copying, and deleting files
The command mv moves or renames files. - The simplest form of use is mv oldfilename newfilename. it will rename the file a.kwd to a new name b.kwd
mv file1 file2 ? Renaming
- It will also move a file to a directory. If you use it in the form mv filename directoryname it will move the file into the named directory keeping its old name
mv file2 \test or mv file2 test
15
Moving, copying, and deleting files
To copy files, you use the cp command. The following will copy file to file2. Note that if file2 doesn't exist, it'll be created, but if it exists, it'll be overwritten
cp file file2
If you want to copy file into directory dir1 cp file dir1
To remove a file from the current directory rm filename
rm file
rm
? remove all files in the current directory
16
Create empty files

• To create an empty file in the current directory
  use the command touch
• touch file1 file2 file3

touch apple banana grape grapefruit watermelon
ls -l
Using file-matching metacharacters

• Metacharacters help to match one or more files
  without typing each filename completely.
• This matches any number of characters(zero or
  more characters).
• ? This matches any one(single) character.
• This matches any one of the characters
  between the brackets, which can include a
  dash-separated rang of letters or numbers.

17
Using file-matching metacharactersThis matches
any number of characters
ls a
apple
ls g
grape grapefruit
ls gt
grapefruit
ls e
apple grape grapefruit watermelon
ls n
banana watermelon
18
Using file-matching metacharacters This
matches any one(single) character ?
ls ????e
Apple grape
ls g???e
grape grapefruit
19
Using file-matching metacharacters This
matches any one of the characters between the
brackets
ls abw
apple banana watermelon
ls agw ne
apple grape watermelon
ls a-g
apple banana grape grapefruit
20
Using file-redirection metacharacters

• lt Direct the contents of a file to the
  command

mail root lt /.bashrc
the contents of the .bashrc file in the home directory are sent in a mail message to the computer's root user.

• gt Direct the output of a command to a file,
  overwriting any existing file

echo I finished the project on (date) gt /projects

• gtgt Direct the output of a command to a file,
  adding the output to the end of
• existing file

echo I finished the project on (date) gtgt /projects
21
echo Command

• Use echo command to display text or value of
  variable.
• echo options string, variables...

22
Quotes

• "Double Quotes
• variables and command substitution(except \ and
  ).
• 'Single quotes
• protects everything enclosed between two single
  quote marks.
• It is used to turn off the special meaning of all
  characters ( NO substitution of variables and
  commands).
• Back quote
• Used with commands only.
• To execute command.

23
command variable
Double Back echo My working directory is pwd The output My working directory is /home/nora/Desktop -
Single Back echo My working directory is pwd The output My working directory is pwd -
Double echo My working directory is pwd The output My working directory is pwd echo the home is HOME The output the home is /home/nora
Single echo My working directory is pwd The output My working directory is pwd echo the home is HOME The output the home is HOME
24
echo Command

• Options-n Do not output the trailing new
  line.-e Enable interpretation of the following
  backslash escaped characters in the strings
• \a alert (bell)\b backspace\n new line\t
  horizontal tab

25
Examples of quoting special characters
ubuntu_at_ubuntu echo n operating system
operating system ubuntu_at_ubuntu
echo e operating \t system
Operating system
echo -e "An apple a day keeps away \a\t\tdoctor\n"
An apple a day keeps away doctor
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References
http//www.podgrid.org/linux-bible/linux-bible-pag
e109.html