Intro:

Perl is a mature, open-source, cross-platform language that takes the best features from other languages such as C, awk, sed, tcl, sh, and BASIC, among others. It's motto is "TMTOWTDI" (There's More Than One Way To Do It): Perl is flexible and allows you to work in the way you prefer.

• Ideal language for Data Munging and Text Processing (essentially what Integration is about)
• More powerful regular expression engine than any other language

e.g. extracting links from a string into a list:

	@links = m/<A[^>]+?HREF\s*=\s*["']?([^'" >]+?)[ '"]?>/sig;

• Many shortcuts to make life easier:
  <> operator
  m//, s///, tr///, etc.
  chomp, chop
  =~ operator
  and so on....

  e.g. copy $my_string to $my_other_string, lowercase all letters, remove "," and "."

    ($my_other_string = $my_string) =~ tr/A-Z,./a-z/d;

e.g. exchanging variables without using temp variables:

    ($a, $b) = ($b, $a);

e.g. implementing "cat" in one line of Perl:

    print <>;

e.g. implementing hl7_rdr in awk vs. perl using a module

	#!/bin/sh

	USAGE="USAGE: $0 data_file"
	if [ ! -f "$1" -a "$1" != "-" ]; then
	   echo "$USAGE" >&2
	   exit 2
	fi

	cat $1 | /usr/ucb/tr "\015" "\012" | 
	nawk -F'|' '{
	   if ( $1 == "" ) {
		  startfield = 2;
	   }
	   else {
		  startfield = 1;
	   }
	   tmpstr = "";
	   for(j=startfield;j<=NF;j++) {
		  if ( length(tmpstr) + length($j) < 80 ) {
			 if ( j == startfield )
				tmpstr = sprintf("%s",$j);
			 else
				tmpstr = sprintf("%s|%s",tmpstr,$j);
		  }
		  else {
			 print tmpstr;
			 tmpstr = sprintf("   |%s",$j);
		  }
	   }
	   print tmpstr;
	}'

vs.

	#!/usr/bin/perl 

	use Text::Wrap qw(wrap $columns $break);

	$columns = 80;
	$break   = qr/(?=\|)/;
	$initial_tab         = "";
	$subsequent_tab      = "   ";

	$/ = "\r";    # input record separator 

	while (<>) {
		tr/\n/\r/;    # convert newlines to carriage returns
		$_ = wrap($initial_tab, $subsequent_tab, $_);
		tr/\r/\n/;    # back to newlines
		print;
	}

• Bottom line: Just about any sort of text processing task is made much easier by using Perl
• Perl vs. Shell scripts + sed, awk, etc.: Uniform toolset that works across many platforms
• Tools such as sed, awk, grep, ls, etc. differ across UNIX/Linux platforms
• These tools also have limitations such as size of lines or limited regex handling
• If you learn Perl, you don't need to know all the differences between tools/Platforms.
• Shell scripts can grow overly complex and cumbersome, hard to maintain
• The Unix philosophy of having many small programs to do one task becomes its weakness after a point
• Don't need pipes, temporary files, or separate processes to do the job
• Perl is very good for system administration tasks

e.g. delete all .log files in current dir that have a modification time older than 3 days

    for (glob("*.log")) {
        unlink if (-f && -M _ > 3);
    }

This would be a significantly longer program in most other languages.

• Large set of built-in and downloadable Modules
• Modules help prevent reinventing large wheels
• Network functions (socket programming, web, ftp, etc.)
• File functions
• Sysadmin modules

e.g. ftp a new NetConfig over to sitedoc's pending dir on makali

    use Net::FTP;

    $ftp = Net::FTP->new("makali.carenet.org", Debug => 1);
    $ftp->login("USER","PASS");
    $ftp->cwd("/hci/root3.7.1P/sitedoc/iig/pending");
    $ftp->put("NetConfig.new");
    $ftp->quit;

• There's More Than One Way To Do It

Example: switch statement

         SWITCH: {
             if (/^abc/) { $abc = 1; last SWITCH; }
             if (/^def/) { $def = 1; last SWITCH; }
             if (/^xyz/) { $xyz = 1; last SWITCH; }
             $nothing = 1;
         }

or

         SWITCH: {
             $abc = 1, last SWITCH  if /^abc/;
             $def = 1, last SWITCH  if /^def/;
             $xyz = 1, last SWITCH  if /^xyz/;
             $nothing = 1;
         }

or

         SWITCH: {
             /^abc/ && do { $abc = 1; last SWITCH; };
             /^def/ && do { $def = 1; last SWITCH; };
             /^xyz/ && do { $xyz = 1; last SWITCH; };
             $nothing = 1;
         }

or

         SWITCH: {
             /^abc/      && do {
                                 $abc = 1;
                                 last SWITCH;
                            };

             /^def/      && do {
                                 $def = 1;
                                 last SWITCH;
                            };

             /^xyz/      && do {
                                 $xyz = 1;
                                 last SWITCH;
                             };
             $nothing = 1;
         }

or

         SWITCH: {
             /^abc/ and $abc = 1, last SWITCH;
             /^def/ and $def = 1, last SWITCH;
             /^xyz/ and $xyz = 1, last SWITCH;
             $nothing = 1; 
         }

or

         SWITCH: for ($where) {
                     /In Card Names/     && do { push @flags, '-e'; last; };
                     /Anywhere/          && do { push @flags, '-h'; last; };
                     /In Rulings/        && do {                    last; };
                     die "unknown value for form variable where: `$where'";
                 }

• Books to Read:
• Learning Perl (good learning resource)
• Perl in a Nutshell (reference)
• Programming Perl (The Bible)
• Perl Pocket Reference (small reference)
• Perl Cookbook (recipes)
• Websites to visit:
• http://www.perl.com (oreilly)
• http://www.perl.org (perl mongers)
• http://use.perl.org (perl news)
• http://perlmonks.org(code examples, questions & answers)
• http://www.cpan.org (Perl Modules)