a) Basics Commands
1.
echo SRM 🡺 to display the string SRM
2.
clear 🡺 to clear the screen
3.
date 🡺 to display the current date
and time
4.
cal 2003 🡺 to display the calendar for
the year 2003 cal 6 2003 🡺 to display the calendar for
the June-2003
5.
passwd 🡺 to change password
6.
free –m 🡺 to view the size of RAM in MB
free –g 🡺 to view the size of RAM in GB
7.
df –h 🡺 to view the disk space
available and used.
8.
uptime 🡺 to view the system up time
9.
bc 🡺 to open a basic calculator
10.
ps 🡺 to view the current terminal
running processes
11.
history 🡺 to get the history of all the
past commands
12.
whoami 🡺 to know which user i am
b) Working with Files
1.
ls 🡺 list files in the present
working directory
ls –l 🡺 list files with detailed
information (long list) ls –a 🡺 list all files including the
hidden files
ls –r root 🡺 list the directory recursively
ls –lh 🡺 list the current location
content in human readable format ls –lt 🡺 to list the files based on
modification time
ls –li 🡺 to view the inode number of
files and directories lscpu 🡺 to view the system
specifications
2.
cat > f1 🡺 to create a file (Press ^d to finish
typing)
3.
cat f1 🡺 display the content of the
file f1
4.
wc f1 🡺 list no. of characters, words
& lines of a file f1 wc –c f1 🡺 list only no. of characters of
file f1
wc –w f1 🡺 list only no. of words of file
f1
wc –l f1 🡺 list only no. of lines of file
f1
5.
cp f1 f2 🡺 copy file f1 into f2
6.
mv f1 f2 🡺 rename file f1 as f2
7.
rm f1 🡺 remove the file f1
8.
head –5 f1 🡺 list first 5 lines of the file
f1 tail –5 f1 🡺 list last 5 lines of the file
f1
c) Working with Directories
1.
mkdir elias 🡺 to create the directory elias
2.
cd elias 🡺 to change the directory as
elias
3.
rmdir elias 🡺 to remove the directory elias
4.
pwd 🡺 to display the path of the
present working directory
5.
cd 🡺 to go to the home directory cd
.. 🡺 to go to the parent directory
cd - 🡺 to go to the previous working
directory cd / 🡺 to go to the root directory
d) File name substitution
1.
ls f? 🡺 list files start with ‘f’ and
followed by any one character
2.
ls *.c 🡺 list files with extension ‘c’
3.
ls [gpy]et 🡺 list files whose first letter
is any one of the character g, p or
y and followed by the word et
4.
ls [a-d,l-m]ring 🡺 list files whose first letter
is any one of the character
from a to d and l to m and
followed by the word ring.
e) I/O Redirection
1.
Input redirection wc –l < ex1 🡺 To find the number of lines of the file ‘ex1’
2.
Output redirection who > f2
🡺 the output
of ‘who’ will be redirected to file f2
3.
cat >> f1 🡺 to append more into the file
f1
f) Piping
Syntax
: Command1 | command2
Output
of the command1 is transferred to the command2 as input. Finally output of the
command2 will be displayed on the monitor.
ex. cat f1 | more 🡺 list the contents of file f1
screen by screen head –6 f1 |tail –2 🡺 prints the 5th & 6th lines of the file f1.
a) Environment variables
1.
echo $HOME 🡺 display the path of the home
directory
2.
echo $PS1 🡺 display the prompt string $
3.
echo $PS2 🡺 display the second prompt
string ( > symbol by default )
4.
echo $LOGNAME 🡺 login name
5.
echo $PATH 🡺 list of pathname where the OS
searches
for
an executable file
b) File Permission
--
chmod command is used to change the access permission of a file.
Method-1
Syntax : chmod [ugo] [+/-] [ rwxa ] filename
u
: user, g : group, o : others
+
: Add permission - : Remove the permission r : read, w : write, x : execute, a
: all permissions
ex. chmod ug+rw f1
adding
‘read & write’ permissions of file f1 to both user and group members.
Method-2
Syntax : chmod octnum file1
The 3 digit
octal number represents as follows
●
first digit --
file permissions for the user
●
second digit --
file permissions for the group
●
third digit --
file permissions for others
Each
digit is specified as the sum of following
4 – read permission, 2 – write permission, 1 – execute
permission ex. chmod
754 f1
it change the file permission
for the file as follows
●
read, write & execute permissions for the user ie; 4+2+1 = 7
●
read, & execute permissions for the group members ie; 4+0+1 =
5
●
only read permission for others ie;
4+0+0 = 4
QUESTIONS FOR PRACTICE:
Q1. Write a command to cut 5 to 8 characters
of the file f1.
$
Q2. Write a command to display user-id of all
the users in your system.
$
Q3. Write a command to paste all the lines of
the file f1 into single line
$
Q4. Write a command to cut the first field of
file f1 and second field of file f2 and paste intothe file f3.
$
Q5. Write a command to change all small case
letters to capitals of file f2.
$
Q6. Write a command to replace all tab character in the file f2 by :
$
Q7. Write a command to check whether the user
judith is available in your system or
not.(use grep)
$
Q8. Write a command to display the lines of
the file f1 starts with SRM.
$
Q9. Write a command to display the name of the
files in the directory
/etc/init.d that contains the pattern grep.
$
Q10. Write a command to display the names of
nologin users. (Hint: the command nologin
is specified in the last filed of the file /etc/passwd for nologin users)
$
Q11. Write a command to sort the file
/etc/passwd in descending order
$
Q12. Write a command to sort the file
/etc/passwd by user-id numerically. (Hint : user-id is in 3rd field)
$
Q13. Write a command to sort the file f2 and write the output into the file f22. Also eliminate duplicate lines.
$
Q14. Write a command to display the unique
lines of the sorted file f21. Also
display the number of occurrences of each line.
$
Q15. Write a command to display the lines that
are common to the files f1 and f2.
$