Perl Script

Pingfei Chen

Introduction

Perl is an acronym that stands for Practical Extraction and Report Language
It is an interpreted programming language known for its power and flexibility
It combines the familiar syntax of C, C++, sed, awk, grep, sh, and csh into a tool that is more powerful than the separate pieces used together
It is an interpreted language optimized for scanning arbitrary text files, extracting information from those text files, and printing reports based on that information
It's also a good language for many system management tasks

What you can do with perl?

ADMINISTRATION scripts
TEXT handling and text processing
INFORMATION servers, clients, and tools
FILE handling, devices, and links with perl
NETWORK programming with perl
NEWS scripts and utilities
FTP scripts and library
DATE and TIME conversion/manipulation
DATABASE and archived file access with perl

Some topics about perl

That First Line

#!/usr/bin/perl

Data Types
three data types: scalars, array of scalars, and associative arrays of scalars
Scalar Variables: Begin with a dollar sign followed by a letter and then letters/numbers
Array of scalars: Begin with a @ sign followed by a letter, and then letters/numbers
Associative array: Begin with a % sign followed by a letter, and then letters/numbers
Examples : $a = 1; $a = "Hi there";
@b = ("one","two","3");
%ages = ("Michael Caine", 39, "Dirty Den", 34, "Angie", 27);
Special Variables

@ARGV holds the command line arguments.

$_ is used by perl for scratch space

< STDIN holds a newline terminated line from STDIN

< STDOUT is a pointer of STDOUT

< STDERR is a pointer of STDERR

Subroutines

A subroutine is like a command you define yourself
Example:

#!/usr/bin/perl

$x = &getnumber;
$y = &getnumber;
$z = $x + $y;
print "$x + $y = $z\n";

sub getnumber {
      print "Type in a number: ";
      $number = <;
      chop($number);
      $number;
}

Control Structures

If/Then/Elsif/Else
Unless the opposite of if
For
While
Until the opposite of while
foreach

File Manipulation

Open function:

open(INFO, $file);            # Open for input
open(INFO, "$file");        # Open for output
open(INFO, "$file");      # Open for appending
open(INFO, "<$file");        # Also open for input

Close function:

close(INFO);

Administration with perl

Add new user accounts
Generate random passwords for adduser
Change ownership of many files
Gripe about easy passwords
Making Backups

Experience with perl

hello.cgi hello.html
env.pl
inf.pl
machine.pl
push.pl