PERL PROGRAMMING

Colorado State University

Computer Science Department

CT 320: Network and System Administration

Original slides from Dr. James Walden at Northern Kentucky University.

Perl Language

Perl is a high-level, general-purpose, interpreted programming language developed for Unix scripting.
Practical Extraction and Reporting Language developed by a Unisys engineer (Larry Wall) for report processing.
Borrows features from C, shell scripting, awk, and sed, including powerful text processing facilities.
Popular for web server, graphics, system admin, and network programs, among other areas.

Source: https://wikipedia.org/wiki/Perl

Perl History

Perl 1 released in 1987 via the comp.sources.misc newsgroup, then expanded rapidly.
Perl 2 released in 1988, with improved regular expressions, Perl 3 in 1989 added binary data streams.
Originally documented by a single manpage, when the Camel Book came out version was bumped to Perl 4.
Perl 5.0 released in 1994, since then many incremental releases, version on CSU machines is 5.22.1 as of June 2016.
Perl 6 is available for Ubuntu, if you install the Rakudo compiler.

Source: https://wikipedia.org/wiki/Perl

Perl Usage (continued)

Web site and web application development
- Internet Movie Database (IMDB)
Test frameworks for web and desktop applications
Configuration management, build, packaging
System administration, periodic tasks
Common Gateway Interface (CGI)
Bioinformatics, Databases, Graphics, etc.

Perl Usage (continued)

Common Gateway Interface (CGI):
- Method for web server software to delegate the generation of web content to executable files.
- A web server that supports CGI can be configured to interpret a URL that it serves as a reference to a CGI script.
- In the case of HTTP PUT or POSTs, the user-submitted data is provided to the program via the standard input.
- The program generates content, writes it to its standard output, and the web server transmits it to the browser.

Source: https://wikipedia.org/wiki/Common_Gateway_Interface

Perl Documentation

Perl Language Reference: http://perldoc.perl.org/index-language.html
Perl Language Tutorials: http://perldoc.perl.org/index-tutorials.html
Perl Community: http://www.perl.org/
Perl Open Source: http://www.cpan.org/
Perl Cheat Sheet: http://perldoc.perl.org/perlcheat.html

Basic Perl

#! /usr/bin/perl -w
print "Hello, world!\n"

Perl Scalars

$alpha = 123456
$beta = 3.14159
$gamma = String

$alpha = 123456;
$beta = 3.14159;
$gamma = "String";
print '$alpha = ' . $alpha . "\n";
print '$beta = ' . "$beta\n";
print "\$gamma = $gamma\n";

Perl has scalar values that can be integer, float, or string.
Perl does not have strong data typing like Java or C++.
Can determine type with a regular expression.
Also there are loadable packages with data type queries.

Perl Math

1 + 2 = 3
3 - 4 = -1
5 * 6 = 30
7 / 8 = 0.875
3 ** 4 = 81
5 % 2 = 1

#! /usr/bin/perl -w
$alpha = 1 + 2;
print "1 + 2 = $alpha\n";
$alpha = 3 - 4;
print "3 - 4 = $alpha\n";
$alpha = 5 * 6;
print "5 * 6 = $alpha\n";
$alpha = 7 / 8;
print "7 / 8 = $alpha\n";
$alpha = 3 ** 4;
print "3 ** 4 = $alpha\n";
$alpha = 5 % 2;
print "5 % 2 = $alpha\n";

Perl Strings

alpha = Foo
beta = Bar
gamma = FooBar
delta = 3
epsilon = BarBarBar

#! /usr/bin/perl -w
$alpha = "Foo";
$beta = 'Bar';
$gamma= $alpha . $beta;
$delta = 3;
$epsilon = $beta x $delta;
print "alpha = $alpha\n";
print "beta = $beta\n";
print "gamma = $gamma\n";
print "delta = $delta\n";
print "epsilon = $epsilon\n";

Declarations

    #! /usr/bin/perl -w
    use strict;
    my $alpha = 42;
    print "alpha is $a1pha";

Global symbol "$a1pha" requires explicit package name at ./typo line 4.
Execution of ./typo aborted due to compilation errors.

Sigils

$alpha = 5;             # alpha is a scalar
@beta = (11,22,33);     # beta is an array
$alpha = $beta[1];      # beta[1] is a scalar, however

$ indicates a scalar
@ indicates an array
% indicates a hash, or associative array

It’s the type of the value, not the type of the variable.

Perl Arrays

# Array Definition
@stuff = ("apples", "pears", "eels");
@numbers = (123, 456, 789, 987, 654, 321);
# Array access
print '$stuff[2] = ', $stuff[2], "\n";
print '$numbers[4] = ', "$numbers[4]\n";

$stuff[2] = eels
$numbers[4] = 654

Perl Arrays (continued)

stuff = apples pears eels eggs lard butter milk
grub = milk
stuff = apples pears eels eggs lard butter

# Adding and removing elements
push(@stuff, "eggs", "lard");
@morestuff = ("butter", "milk");
push(@stuff, @morestuff);
print "stuff = @stuff\n";
$grub = pop(@stuff);
print "grub = $grub\n";
print "stuff = @stuff\n";

Perl Arrays (continued)

# Length versus contents
$x = @stuff;
print '$x = ' . "$x\n";
$x = "@stuff";
print '$x = ' . "$x\n";

$x = 6
$x = apples pears eels eggs lard butter

File I/O

    #! /usr/bin/perl -w
    # File Input
    open(INFO, "whatever");
    @lines = <INFO>;
    close(INFO);
    print @lines;

C programmers manipulate arrays element-by-element
Perl programmers manipulate arrays as a single entity

File I/O

    # File modes
    open(INFO, "datafile");   # Open for input
    open(INFO, ">datafile");  # Open for output
    open(INFO, ">>datafile"); # Open for append
    open(INFO, "<datafile");  # Open for input

File Output

    open(FILE, ">temp.txt");
    print FILE "This line goes to the file.\n";
    close(FILE);

Perl Loops

do while 0
do while 1
do while 2
do while 3
while 2
while 1
while 0
for 4
for 5
for 6

#! /usr/bin/perl -w
$i = 0;
do {
    print "do while $i\n";
} while $i++ < 3;

$j = 3;
while ($j-- > 0) {
    print "while $j\n";
}

for $var (4..6) {
    print "for $k\n";
}

# or a C-style for-loop

Perl Functions

# Subroutine
sub total {
    $sum = 0;
    foreach $item (@_) {
        $sum += $item;
    }
    return $sum;
}
# Main program
@data1 = (1,2,3,4);
$answer = total(@data1);
print "Sum of @data1 is $answer\n";

Sum of 1 2 3 4 is 10

System Calls

Sun Apr 28 22:25:40 MDT 2024
one
two
greybull

$a = `date`;        # Note backquotes
print $a;           # Includes a newline

@info = `head -4 numbers`;
#print @info;
print $info[0];     # first line
print $info[1];     # second line

$status = system("cat /etc/hostname");

Admin Example

Nameservers from /etc/resolv.conf
192.168.0.1
205.171.3.25

$path = "/etc/resolv.conf";
open (CONFIG, $path);
print "Nameservers from $path:\n";
while (<CONFIG>) {
    chomp;
    @values = split(' ', $_);
    print "$values[1]\n"
        if lc($values[0]) eq "nameserver";
}

Perl Packages

Perl offers a set of modules, just as Java has packages, that contain domain-specific functionality:
- Security and Encryption
- Internationalization and Locale
- Database Interfaces
- User Interfaces
- Data Type Utilities
- Archiving and Compresion
- etc., etc., etc.

Source: http://www.cpan.org/modules/

Perl Features

Other Perl language features:
- Arrays: merge, append, sort
- Hashing: create, append, print
- Regular Expressions: matching, substitution
- Parameter Passing
- Operator Precedence
- Hexadecimal and Binary Conversion
- Creating Packages
- Database Connectivity
- Object Oriented Perl

Source: http://linuxconfig.org/perl-programming-tutorial/

CT320: Network and System Administration

Fall 2016

Perl

PERL PROGRAMMING

Perl Language

Perl History

Perl Usage (continued)

Perl Usage (continued)

Perl Documentation

Basic Perl

Perl Scalars

Perl Math

Perl Strings

Declarations

Sigils

Perl Arrays

Perl Arrays (continued)

Perl Arrays (continued)

File I/O

File I/O

File Output

Perl Loops

Perl Functions

System Calls

Admin Example

Perl Packages

Perl Features