This document provides an introduction and overview of Linux commands and Perl basics. It discusses key Linux commands for system information, user management, files/directories, permissions, processes, networking and more. It also covers Perl data types, variables, input/output, strings, arithmetic, comparisons, functions and file handling. The document aims to teach Linux commands and Perl programming basics.

1. PERL BASICS
LINUX
&
BY:- SAGAR KUMAR

2. Introduction to Linux
o Open source Operating System
o Developed by Linus Torvalds
o Architecture of Linux operating system

3. Linux Basic Commands:
o SYSTEM & HARDWARE INFORMATION
o USER INFORMATION AND MANAGEMENT
o FILE AND DIRECTORY COMMANDS
o PROCESS MANAGEMENT
o FILE PERMISSIONS
o NETWORKING
o ARCHIVES (TAR FILES)
o SEARCH
o FILE TRANSFERS
o DIRECTORY NAVIGATION

4. System & Hardware Information:-
o uname –a #Display Linux system information
Linux aa34faf8af0b 3.10.0514.26.2.el7.x86_64 #1 SMP Tue Jul 4 15:04:05 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
o uname –r #Dispaly kernel release information
3.10.0-514.26.2.el7.x86_64
o uptime #for how long system has been running
11:56:15 up 14 days, 21:18, 0 users, load average: 23.14, 24.23, 24.68
o hostname #gives hostname of the system
cb.vu
o hostname –I #gives IP address of the Host
78.31.70.238
o last reboot #to check when the system has been last rebooted
wtmp begins Sat Sep 9 10:24:23 2017
o date #display the date and time
Mon Jan 01 2018 17:17:33 GMT+0530 (India Standard Time)
o cal #display current month calendar
o free #Display the free and used memory (-h for human readable, -m for MB, -g for GB)
total used free shared buff/cache available
Mem: 263861664 11205028 205258364 1867876 47398272 233338992
Swap: 4194300 1756284 2438016

5. User Information and Management:-
o w #show who is logged in and what they are doing.
12:07:00 up 14 days, 21:29, 0 users, load average: 21.66, 24.14, 24.30
USER TTY LOGIN@ IDLE JCPU PCPU WHAT
o who #who is logged into the system
o whoami #who are you logged in as
[2018-01-01 17:41.43] ~
[SAGAR.workgroup] ➤ whoami
SAGAR
o id #display the current user id and group id
[2018-01-01 17:41.49] ~
[SAGAR.workgroup] ➤ id
uid=1001(SAGAR) gid=513(UsersGrp) groups=1002(HomeUsers),1004(ORA_DBA),559(Performance Log Users),545(Users)
o last #who logged in last

6. Files and Directories Commands:
o ls –al #lists all file in long listed format
o ll #actually aliased to `ls -l'
o pwd #shows present working directory
o mkdir directory_name #creates a new directory
o rmdir directory_name #deletes an empty directory
o rm –r directory_name #deletes the directory and its contents
o rm filename #deletes a file
o cp file1 file2 #copy one file to another
o mv file1 file2 #move a file/ rename a file
o touch filename #create a new file
o cat filename #displays the file contents

7. File Permissions:
• There are 3 types of users
1. User(u) 2. Group(g) 3. Others/ World(o)
• Below are the permissions types
• Read= r
• Write= w
• Execute = x
• No access = -
• Commands to change the permissions of the file:- chmod
example:- chmod 755 filename
1/0 1/0 1/0
r = - - -
w = - - -
x = - - -
Example: rwx rwx rwx chmod 777 filename

8. Archives (Tar files):
o tar -cf archive.tar directory # Create tar named archive.tar containing directory.
o tar -xf archive.tar # Extract the contents from archive.tar.
o tar -czf archive.tar.gz directory # Create a gzip compressed tar file name archive.tar.gz.
o tar -xzf archive.tar.gz # Extract a gzip compressed tar file.
Directory Navigation:
o cd .. # To go up one level of the directory tree. (Change into the parent directory.)
o cd # Go to the $HOME directory
o cd /etc # Change to the /etc directory
o cd - # go back to previous directory (last accessed dir)

9. Process Management:
o ps #your currently running processes
o ps –ef #all the currently running processes on the system
o ps- -ef |grep processname #process information for process name
o kill pid #kill a process
o top #display and manage the top processes
o killall processname #kill all processes named there
o program & #start program in the background
o bg #display stopped or background processes
o fg #bring the most recent backgroungd job to foreground

10. Networking:
o ifconfig #Displays network interface and ip address
o ping #to check given address is alive or not
o dig domain_name #display DNS information for domain
o dig –x IP_Address #Reverse lookup of IP_Address
o host domain #display DNS IP address for domain
o hostname #display the hostname
[2018-01-01 19:06.49] ~
[SAGAR.workgroup] ➤ hostname
workgroup
o netstat #Display listening tcp and udp ports and corresponding programs
[2018-01-01 19:11.20] ~
[SAGAR.workgroup] ➤ netstat
Active Connections
Proto Local Address Foreign Address State
TCP 10.10.156.9:4280 hk2sch130022025:https ESTABLISHED
TCP 10.10.156.9:4294 sb-in-f188:5228 ESTABLISHED
TCP 10.10.156.9:6010 static:https ESTABLISHED
TCP 10.10.156.9:9327 static:https ESTABLISHED
TCP 10.10.156.9:9635 13.75.42.223:https TIME_WAIT

11. SEARCH:
o grep pattern file # Search for pattern in file
o grep -r pattern directory # Search recursively for pattern in directory
o locate name # Find files and directories by name
o find /home/Dir -name 'prefix*’ # Find files in /home/Dir that start with "prefix".
o find /home -size +100M # Find files larger than 100MB in /home
File Transfer:
o scp file.txt server:/tmp # Secure copy file.txt to the /tmp folder on server
o scp server:/var/www/*.html /tmp # Copy *.html files from server to the local /tmp folder.
o scp -r server:/var/www /tmp # Copy all files and directories recursively from server
to the current system's /tmp folder.

12. File Editing:
o Most common editor in Linux -- vi editor
o Commands for editing files in vi editor
o vi filename # to open file in editor (Command mode)
o Press “i” # to go in INSERT mode
o double esc # moving to command mode
o :w #to save changes
o :q #to exit
o :q! #force exit
o :wq #save changes and exit
o Commands for movement inside a file
o h, j, k ,l #left, down, up
o $ #to end of a line
o ^ #to the beginning of a line
o G #end of a file
o :1 #to the beginning of a file
o :47 #to the given line (here on 47th line)

13. Editing file in vi editor
o dd #remove a line
o 5dd #remove 5 lines
o u #undo last action
o :s/string #searching a string in file
o :s/string/replace #search and replace a string in current line
o :%s/string/replace #search and replace a string in whole file
o :%s/string/replace/i #search and replace a string in whole file(Case Insensitive)

14. Introduction to PERL:
o PERL : Practical Extraction and Report Language
o Developed by Larry Wall in 1987
o It is a interpreted language
o Code written in Perl is called Perl Script
o Most recent version of Perl -Perl 5.24.3 released on 22-09-2017

15. Basic Syntax:
o Statements ends with semicolon (;)
o Comments starts with #
o Variables:
o You don’t have to declare a variable type
o Identifiers:
o A variable name
o Case Sensitive

16. o Example of perl Script :
#perl 5.22.1 ----------------- Perl version in comment
use strict; ----------------- Compiler flag for writing perl in strict way
use warnings; ----------------- Compiler flag for runtime warnings
print "Hello, World";-------------- Print statement for displaying output
 Save this file with .pl extention (say – Hello.pl)
 Execution of the Script : (on LINUX platform)
1. perl Hello.pl / perl –w Hello.perl
or
2. Make the perl file executable
chmod 700 Hello.pl
Execute with the following command:
./Hello.pl

17. Data types in Perl:
Perl language is a loosely typed language, the Perl interpreter itself chooses the data type
There are basically three data types in Perl
1. Scalars : Perl scalars are a single data item. A scalar can be a
number, a reference (address of a variable) or a string.
Scalars are preceded by ‘$’ sign.
Eg:- $name = “Sagar”;
$age = 24;
2. Arrays : Arrays are an ordered list of scalars.
They are preceded by ‘@’ sign.
Eg:- @arr = (1, 2, 3);
@arr_str = (“happy”, “new”, “year”);
3. Hashes : Hashes are an unordered collection of key-value pairs.
They are preceded by ‘%’ sign.
Eg:- %hashName = (
“Ram" => 24;
“Raman” => 26; );

18. User input in Perl Programming:
o For user input : <STDIN> or <>
Example : userInput.pl
#perl 5.22.1
use strict;
use warnings;
print "Enter your Name:n";
my $name = <STDIN>;
say "Welcome $name";
Execution: perl userInput.pl (Enter)
Output: Enter your Name:
Sagar
Welcome Sagar

19. String Operation Arithmetic
lt less than <
gt greater than >
eq equal to ==
le less than or equal to <=
ge greater than or equal to >=
ne not equal to !=
cmp compare, return 1, 0, -1 <=>
Comparison Operators:

20. Operator Operation
||, or logical or
&&, and logical and
!, not logical not
xor logical xor
Logical Operators
Operator Operation
. string concatenation
x string repetition
.= concatenation and assignment
$string1 = “Hello";
$string2 = “World";
$newstring = $string1 . $string2; #“HelloWorld"
$newerstring = $string1 x 2; #“Hello"
$string1 .= $string2; #“HelloWorld"
String Operators

21. Functions in Perl:
o Functions in Perl are known as Subroutines
o Subroutines are created with sub keyword
Example:
#!/usr/bin/perl
# Function definition
sub Hello {
print "Hello, World!n";
}
# Function call
Hello();

22. Predefined subroutines for Arrays:
Sr.No. Types & Description
1 push @ARRAY, LIST
Pushes the values of the list onto the end of the array.
2 pop @ARRAY
Pops off and returns the last value of the array.
3 shift @ARRAY
Shifts the first value of the array off and returns it, shortening the
array by 1 and moving everything down.
4 unshift @ARRAY, LIST
Prepends list to the front of the array, and returns the number of
elements in the new array.

23. Example for Arrays subroutines:
#perl 5.22.1
use strict;
use warnings;
my @arr;
print "Enter the number of element you want to enter n"; #Enter Size
my $n = <STDIN>;
print "n Enter the elements n"; # Enter Elements
for (my $i= 0; $i<$n; $i++){
my $ele = <STDIN>;
$arr[$i]=$ele;
}
print "Entered Elements are : --- n"; #print Elements
for (my $i= 0; $i<$n; $i++){
print $arr[$i];
}
print "Size of the array is : - ".scalar @arr."n"; # get Size
print "Your sorted array is : -n";
my @sorted_arr = sort(@arr); #sort Array
print @sorted_arr;
print "After Element pushingn";
push(@sorted_arr, "99n"); #add one Element at the end of array
print @sorted_arr;
print "New size of the array is :---".scalar @sorted_arr."n";
print "After unshifting ---- Adding element at begining n";
unshift (@sorted_arr,"555n"); #add element at the begining of the array
print @sorted_arr;
print "After poping ------ removing element from end n";
pop(@sorted_arr);
print @sorted_arr;
print "After shifting ------ removing element from beginning n";
shift(@sorted_arr);
print @sorted_arr;
OUTPUT:
Size of the array is : - 3
Your sorted array is : -
3
7
9
After Element pushing
3
7
9
99
New size of the array is :---4
After unshifting ---- Adding element at begining
555
3
7
9
99
After poping ------ removing element from end
555
3
7
9
After shifting ------ removing element from beginning
3
7
9

24. o File Handling :
Eg:
#perl 5.22.1
open(DATA, "<file.txt") or die "Couldn't open file file.txt, $!";
while(<DATA>) { print "$_"; }
o File opening modes:
Sr.No. Entities & Definition
1 < or r
Read Only Access
2 > or w
Creates, Writes, and Truncates
3 >> or a
Writes, Appends, and Creates
4 +< or r+
Reads and Writes
5 +> or w+
Reads, Writes, Creates, and Truncates
6 +>> or a+
Reads, Writes, Appends, and Creates

25. Regular Expression in Perl:
o There are three regular expression operator in Perl
1. Match Regular Expression - m//
2. Substitute Regular Expression - s///
3. Transliterate Regular Expression - tr///
Example: my $str = “Hello, World! Happy New Year ”;
Match operator : $str =~ m/Happy/ #true
Substitute operator: $str =~ s/World/India/; #will replace World with India(only first occurrence)
Translator operator: $str = ~tr/World/India/;#will replace all occurrence of World to India

26. Thank You