LINUX COMMANDS
● ls - list
directory contents
$ ls
file1 sub_dir1
● who am i – this
command identifies the invoking user and list the username, terminal line ,date
and time of login
$ who am i
anuj pts/1 2015-01-03 17:10 (:0)
● who - (show
who is logged on) this is more powerful than who am i . It displays the data about all the users that have logged
into the system . It is crucial for multi-user operating system
$ who
anuj tty7 2015-01-03 16:31 (:0)
anuj pts/1 2015-01-03 17:10 (:0)
● pwd print name of current/working directory
$ pwd
/home/anuj/dir1
● mkdir make directories
● rmdir remove
empty directories
$ mkdir dir3
$ ls
dir3 file1
sub_dir1
$ rmdir dir3
$ ls
file1 sub_dir1
$ rmdir sub_dir1
rmdir:
failed to remove `sub_dir1': Directory not empty
● cd change
directory
$ cd sub_dir1
/sub_dir1$
● man - an interface to the on-line
reference manuals . man is the system's manual pager.
/sub_dir1$ man pwd
// this will generate the manual for the command
● clear clear
screen
File
Manipulation
cat
concatenate files and print on the standard output
● Create
file
$ cat > file1
this
is a file
// press CTRL + D to come out of the file typing
section
● view
file
/sub_dir1$ cat file2
this
is my second file which is in direcotry sub_dir1 wich is a sub-directory of
dir1
● view 2
files simultaneously
// here file1 is a file in this directory and file2 is
a file in a subdirectory named sub_dir1
//So we have written full path of file2
$ cat file1 sub_dir1/file2
this
is a file
this
is my second file which is in direcotry sub_dir1 wich is a sub-directory of
dir1
● view 3
or more files
$ cat file1 sub_dir1/file2 file1
this
is a file
this
is my second file which is in direcotry sub_dir1 wich is a sub-directory of
dir1
this
is a file
● copy
files
● move
file
// this shows directory contents
$ ls
file1 sub_dir1
$ mv
sub_dir1/file3 dir1
// this now shows the new directory contents
$ ls
dir1 file1
sub_dir1
● delete
file
// this shows directory contents
$ ls
dir1 file1
sub_dir1
$ rm file1
// this now shows the new directory contents
$ ls
dir1 sub_dir1
Calculator
$ bc
bc
1.06.95
Copyright
1991-1994, 1997, 1998, 2000, 2004, 2006 Free Software Foundation, Inc.
This
is free software with ABSOLUTELY NO WARRANTY.
For
details type `warranty'.
5+4
9
2+5*8
42
2+5*8/4
12
WildCard
Characters
*
character : It represents all characters including an empty space
//
we have tried to match the sub_dir1 directory
$ ls -x *_dir1
file2
// we got our match but the terminal
display its sub – files
?
character : It represents a single character
$ ls d???
dir1
[]
enclose a list of character where the match is on any single character
enclosed in the bracket
$ ls d[i]*
dir1
Ownership
& Protection
There
are 3 classes of user who may have access to a file :
Owner:
The owner is the user who initially created the file.
Group:
Several users can be combined into a usergroup & so there is a group
ownership associated with each file & directory.
Public:
All other users od Unix system that is , anyone who has a username and can gain
access to the system.
There
are 3 types of permission :
Read:
User can look at the contents of that file.
Write:
User can change the contents of that file.
Execute:
User can use the file as a Unix command.
changing
Permission with chmod
Two
ways for doing this:
-
As an absolute value given as an octal number.
-Symbolic
mode
1)
Absolute Value
$ cat > file1
this
is your file
$ ls -l
total
4
-rw-rw-r--
1 anuj anuj 18 Jan 7 21:04 file1
$ chmod 644 file1
$ ls -l
total
4
-rw-r--r--
1 anuj anuj 18 Jan 7 21:04 file1
$ chmod 777 file1
$ ls -l
total
4
-rwxrwxrwx
1 anuj anuj 18 Jan 7 21:04 file1
2)
Symbolic Mode
$
cat > file1
this
is your file
$
ls -l
total
4
-rw-rw-r--
1 anuj anuj 18 Jan 7 21:04 file1
$
chmod a=r,u=r+w+x file1
$
ls -l
total
4
-rwxr--r--
1 anuj anuj 18 Jan 7 21:04 file1
User
Mask
umask - set file mode creation mask
$umask
0002
$umask
777
$
umask
0777
Input
Output Process
Three
standard files:
-
Standard Input
- Standard Output
-Diagnostic Output
-
Redirecting Standard Input
$ cat file1 > sub_dir1/file3
// you can check the contents by using cat command
$ cat
sub_dir1/file3
this
is a file
- Redirecting Standard Output
$ ls -l >list_file
// you can check the contents by
using cat command
$ cat list_file
total 76
drwxr-xr-x 2 anuj anuj 4096 Jan
8 08:20 Desktop
drwxr-xr-x 2 anuj anuj 4096 Jan
4 19:25 Documents
drwxr-xr-x 2 anuj anuj 4096 Jan
8 19:06 Downloads
-rw-r--r-- 1 anuj anuj 8445 Jan
4 19:18 examples.desktop
-rw-rw-r-- 1 anuj anuj 26032
Jan 8 18:35 linux_1348129829.jpg
-rw-rw-r-- 1 anuj anuj 0 Jan
8 19:16 list_file
drwxr-xr-x 2 anuj anuj 4096 Jan
4 19:25 Music
drwxrwxr-x 2 anuj anuj 4096 Jan
7 21:04 npgc
drwxr-xr-x 2 anuj anuj 4096 Jan
4 19:25 Pictures
drwxr-xr-x 2 anuj anuj 4096 Jan
4 19:25 Public
drwxr-xr-x 2 anuj anuj 4096 Jan
4 19:25 Templates
drwxr-xr-x 2 anuj anuj 4096 Jan
4 19:25 Videos
-Appending Standard Output
$ cat > xy_file
this is a file
anuj@anuj-G31M-ES2L:~$ cat >
xy2_file
i want to append this to xy_file
anuj@anuj-G31M-ES2L:~$ cat
xy2_file>>xy_file
anuj@anuj-G31M-ES2L:~$ cat xy_file
this is a file
i want to append this to xy_file
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