Dealing with Legacy Perl Code - Peter Scott

1. Maintaining Code While Staying Sane Peter Scott O’Reilly School of Technology February 2011

2. Dealing With Legacy Perl <ul><li>Legacy Perl can stink </li></ul><ul><li>Even when you wrote it </li></ul><ul><li>Or especially when you wrote it </li></ul><ul><li>But Why? </li></ul>

3. Why So Many Ugly Perl Programs? <ul><li>Unfortunately, some of those ways stink </li></ul><ul><li>Or, people use more than one way of doing the same thing in the same program </li></ul>

4. The “DWIM” Myth <ul><li>“ Perl programming doesn’t require the same discipline as other languages” </li></ul><ul><li>Indeed; it may require more </li></ul><ul><ul><li>So many WTDI </li></ul></ul><ul><li>Cure: Adopt best practices </li></ul>

5. The “Prototyping Only” Myth <ul><li>“ Perl is too slow and/or unpredictable to be used for serious work” </li></ul><ul><li>Too slow - sometimes, not always when you’d expect it </li></ul><ul><li>Unpredictable - only when programming without discipline or understanding </li></ul><ul><li>Cure: Learn algorithms, profiling, benchmarking </li></ul>

6. The “$@%*!” Myth <ul><li>“ Perl is a write-only language” </li></ul><ul><li>Another product of insufficient discipline </li></ul><ul><li>The dark side of TMTOWTDI </li></ul><ul><li>Cure: Adopt best practices, eschew obfuscation </li></ul>

7. Find the Author(s)! <ul><li>Are they a better programmer than you or worse? </li></ul><ul><li>Especially, better or worse at Perl? </li></ul><ul><li>This helps you evaluate code you don’t understand </li></ul><ul><ul><li>If you find code you don’t understand, it may be wrong </li></ul></ul><ul><ul><li>Or it may be right, and over your head </li></ul></ul><ul><li>What was their background? </li></ul><ul><ul><li>A Shell programmer uses different idioms from a C++ programmer </li></ul></ul>

8. What Are You Dealing With? <ul><li>What was the code optimized for? </li></ul><ul><ul><li>Maintainability </li></ul></ul><ul><ul><li>Performance </li></ul></ul><ul><ul><li>Brevity </li></ul></ul><ul><ul><li>Job security </li></ul></ul><ul><ul><li>Something else? </li></ul></ul>

9. Maintainability <ul><li># Print words with an even number of letters, AND even </li></ul><ul><li># number of each vowel, AND even position in the input </li></ul><ul><li># (input is a dictionary that has one word per line) </li></ul><ul><li>OUTER: while (<>) </li></ul><ul><li>{ </li></ul><ul><li>next if $. % 2; </li></ul><ul><li>chomp; </li></ul><ul><li>next if length() % 2; </li></ul><ul><li>for my $vowel (qw/a e i o u y/) </li></ul><ul><li>{ </li></ul><ul><li>my @vowels = /$vowel/g; </li></ul><ul><li>next OUTER if @vowels %2; </li></ul><ul><li>} </li></ul><ul><li>print "$_n"; </li></ul><ul><li>} </li></ul>

10. Performance <ul><li>while (<>) </li></ul><ul><li>{ </li></ul><ul><li>next if ($. | length() - 1)) % 2; </li></ul><ul><li>next if tr/e// % 2; </li></ul><ul><li>next if tr/a// % 2; </li></ul><ul><li>next if tr/i// % 2; </li></ul><ul><li>next if tr/o// % 2; </li></ul><ul><li>next if tr/u// % 2; </li></ul><ul><li>next if tr/y// % 2; </li></ul><ul><li>print; </li></ul><ul><li>} </li></ul>

11. Brevity <ul><li>#!/usr/bin/perl -ln </li></ul><ul><li>($x=aeiouy)=~s#.#y/$&//|#g;eval("$x$.|y///c")%2&&next;print </li></ul>

12. Job Security <ul><li>@i = map { chop; $x++ %2 ? $_ : () } <>; </li></ul><ul><li>while ($i = shift @i) </li></ul><ul><li>{ </li></ul><ul><li>ord(pack "w/a*", $i) & 1 and next; </li></ul><ul><li>$_ = "$in"; </li></ul><ul><li>$i =~ s/$_(.*)$_/$1/ for qw/a e i o u y/; </li></ul><ul><li>print unless $i =~ /[aeiouy]/; </li></ul><ul><li>} </li></ul>

13. Testing <ul><li>You can’t test too early </li></ul><ul><ul><li>Or too much </li></ul></ul><ul><ul><li>Use Test::More </li></ul></ul><ul><li>Also useful: </li></ul><ul><ul><li>Test::Exception </li></ul></ul><ul><ul><li>Test::Inline </li></ul></ul><ul><ul><li>Test::NoWarnings </li></ul></ul>

14. Tests are Real Programs, Too <ul><li>Don’t abandon good indentation, variable naming, design, etc just because they’re “tests” </li></ul><ul><ul><li>Follow good development practices </li></ul></ul><ul><ul><li>use strict and use warnings in them </li></ul></ul><ul><ul><li>Abstract common code to modules in t/ </li></ul></ul><ul><li>Keep tests small </li></ul><ul><li>They’ll grow anyway </li></ul><ul><li>Refactor as necessary </li></ul><ul><li>It’s fine for tests to prompt for passwords, etc </li></ul>

15. Testing Web Applications <ul><li>Good design would mean you wouldn't have to go through a web server, of course </li></ul><ul><li>Start out simple by using WWW::Mechanize </li></ul><ul><ul><li>Acts like a virtual browser </li></ul></ul><ul><ul><li>Easy to navigate and fill in forms </li></ul></ul>

16. Web Testing Example <ul><li>my $ua = WWW::Mechanize->new; </li></ul><ul><li>my $res = $ua->get("http://www.example.com/"); </li></ul><ul><li>ok( $res->is_success, "Got first page") </li></ul><ul><li>or die $res->message; </li></ul><ul><li>$ua->set_visible($username, $password); </li></ul><ul><li>ok( $ua->submit->is_success, "Logged in" ) </li></ul><ul><li>or die $ua->res->message; </li></ul>

17. Modern Web Testing <ul><li>Now you can use Test::WWW::Mechanize </li></ul><ul><ul><li>$mech->get_ok(...) </li></ul></ul><ul><ul><li>$mech->title_like(...) </li></ul></ul><ul><ul><li>$mech->content_contains(...) </li></ul></ul><ul><ul><li>$mech->follow_link_ok(...) </li></ul></ul><ul><ul><li>$mech->has_tag_like(...) </li></ul></ul><ul><ul><li>etc </li></ul></ul>

18. Layout <ul><li>Code should be pretty to look at </li></ul><ul><li>Add comments where you had to think a lot </li></ul><ul><li>What’s your role? </li></ul><ul><li>Don’t reformat if it doesn’t belong to you </li></ul><ul><li>Use perltidy to fix up even the worst layout </li></ul>

19. Before perltidy <ul><li>for my $word (keys %{$word{$len}}){ </li></ul><ul><li>chop(my $prefix = $word);if ($opt{g}){ </li></ul><ul><li>while( $prefix ){ </li></ul><ul><li>if(my $words=delete$chain{ $prefix} ){ $chain{$word} = [ @$words, $word ]; </li></ul><ul><li>$maxcount=max ($maxcount,@$words+1); last;} </li></ul><ul><li>chop $prefix; } </li></ul><ul><li>}else{ if (my $words = delete </li></ul><ul><li>$chain{$prefix}){$chain{$word} = [@$words, </li></ul><ul><li>$word]; $changed = 1;} }} </li></ul>

20. After perltidy <ul><li>for my $word (keys %{$word{$len}}) { </li></ul><ul><li>chop(my $prefix = $word); </li></ul><ul><li>if ($opt{g}) { </li></ul><ul><li>while ($prefix) { </li></ul><ul><li>if (my $words = delete $chain{$prefix}) { </li></ul><ul><li>$chain{$word} = [@$words, $word]; </li></ul><ul><li>$maxcount = max($maxcount, @$words + 1); </li></ul><ul><li>last; </li></ul><ul><li>} </li></ul><ul><li>chop $prefix; </li></ul><ul><li>} </li></ul><ul><li>} </li></ul><ul><li>else { </li></ul><ul><li>if (my $words = delete $chain{$prefix}) { </li></ul><ul><li>$chain{$word} = [@$words, $word]; </li></ul><ul><li>$changed = 1; </li></ul><ul><li>} </li></ul><ul><li>} </li></ul><ul><li>} </li></ul>

21. After perltidy <ul><li>for my $word (keys %{$word{$len}}) </li></ul><ul><li>{ </li></ul><ul><li>chop(my $prefix = $word); </li></ul><ul><li>if ($opt{g}) </li></ul><ul><li>{ </li></ul><ul><li>while ($prefix) </li></ul><ul><li>{ </li></ul><ul><li>if (my $words = delete $chain{$prefix}) </li></ul><ul><li>{ </li></ul><ul><li>$chain{$word} = [@$words, $word]; </li></ul><ul><li>$maxcount = max($maxcount, @$words + 1); </li></ul><ul><li>last; </li></ul><ul><li>} </li></ul><ul><li>chop $prefix; </li></ul><ul><li>} </li></ul><ul><li>} </li></ul><ul><li>else </li></ul><ul><li>{ </li></ul><ul><li>if (my $words = delete $chain{$prefix}) </li></ul><ul><li>{ </li></ul><ul><li>$chain{$word} = [@$words, $word]; </li></ul><ul><li>$changed = 1; </li></ul><ul><li>} </li></ul><ul><li>} </li></ul><ul><li>} </li></ul>

22. Analysis <ul><li>Eliminate superfluous code through coverage analysis: </li></ul><ul><ul><li>Devel::Coverage </li></ul></ul><ul><ul><li>Devel::Cover </li></ul></ul><ul><li>Improve speed through profiling: </li></ul><ul><ul><li>Devel::Dprof </li></ul></ul><ul><ul><li>Devel::NYTProf </li></ul></ul>

23. Devel::NYTProf <ul><li>Very new </li></ul><ul><li>Incredibly flexible and accurate </li></ul><ul><li>Terrific reporting </li></ul>

24. Devel::NYTProf

25. What to Look Out For in Inherited Code <ul><li>Apparent level of Perl expertise </li></ul><ul><ul><li>Uses hashes? Regexes? </li></ul></ul><ul><ul><li>Uses parallel arrays/hashes instead of LoLs? </li></ul></ul><ul><ul><li>Calls unnecessary external programs? </li></ul></ul><ul><li>What version of Perl was it apparently developed for? </li></ul><ul><ul><li>Uses my ? Or local ? Uses use ? </li></ul></ul><ul><li>Cargo Cult Perl </li></ul>

26. The Documentation Hound <ul><li>########################################## </li></ul><ul><li># Function name: increment_number </li></ul><ul><li># Author: John Q. Lifer </li></ul><ul><li># Date Created: 1996-07-14 13:45:22 PDT </li></ul><ul><li># Last modified: 2005-03-21 11:09:32 PST </li></ul><ul><li># Inputs: Number </li></ul><ul><li># Outputs: None </li></ul><ul><li># Returns: Input number plus one </li></ul><ul><li># Exceptions: none </li></ul><ul><li># Change history: </li></ul><ul><li># 1996-07-21: Fixed off by one bug - jql </li></ul><ul><li># 2002-10-23: Changed obfuscatory ++ operator - jql </li></ul><ul><li>########################################## </li></ul><ul><li>sub increment_number { </li></ul><ul><li>### Formal parameter list </li></ul><ul><li>my ($num) = @_; </li></ul><ul><li>### Function body </li></ul><ul><li># TODO: Throw exception on missing input, NaN, etc... - jql </li></ul><ul><li>$num = $num + 1; # Add one to $num </li></ul><ul><li>return $num; </li></ul><ul><li>} </li></ul>

27. The Documentation Hound <ul><li>########################################## </li></ul><ul><li># Function name: increment_number </li></ul><ul><li># Author: John Q. Lifer </li></ul><ul><li># Date Created: 1996-07-14 13:45:22 PDT </li></ul><ul><li># Last modified: 2005-03-21 11:09:32 PST </li></ul><ul><li># Inputs: Number </li></ul><ul><li># Outputs: None </li></ul><ul><li># Returns: Input number plus one </li></ul><ul><li># Exceptions: none </li></ul><ul><li># Change history: </li></ul><ul><li># 1996-07-21: Fixed off by one bug - jql </li></ul><ul><li># 2002-10-23: Changed obfuscatory ++ operator - jql </li></ul><ul><li>########################################## </li></ul><ul><li>sub increment_number { </li></ul><ul><li>### Formal parameter list </li></ul><ul><li>my ($num) = @_; </li></ul><ul><li>### Function body </li></ul><ul><li># TODO: Throw exception on missing input, NaN, etc... - jql </li></ul><ul><li>$num = $num + 1; # Add one to $num </li></ul><ul><li>return $num; </li></ul><ul><li>} </li></ul>

28. The Documentation Hound Cure <ul><li>s/^#+n//mg </li></ul><ul><li>Move to POD later in this file </li></ul><ul><ul><li>Or maybe another file </li></ul></ul><ul><ul><ul><li>Such as /dev/null </li></ul></ul></ul><ul><ul><li>But keep function/method signatures and descriptions </li></ul></ul><ul><li>Make the code tell the story </li></ul><ul><li>Preserve comments that answer 'Why?' </li></ul>

29. The Documentation Hound Cure <ul><li>For local programs, author and history information can be taken care of by a source code control system </li></ul><ul><li>For distributions: </li></ul><ul><ul><li>Move author information to a README or POD AUTHOR section </li></ul></ul><ul><ul><li>Move history information to change log </li></ul></ul>

30. String Manipulation, BASIC-Style <ul><li>$repl = ' '; </li></ul><ul><li>for ($off = 0; $off < length($str); $off++) { </li></ul><ul><li>$c = substr($str, $off, 1); </li></ul><ul><li>if (index("012345789", $c) < 0) { </li></ul><ul><li>substr($str, $off, 1, $repl); </li></ul><ul><li>$off-- unless $repl; </li></ul><ul><li>$repl = ''; </li></ul><ul><li>} </li></ul><ul><li>else { </li></ul><ul><li>$repl = ' '; </li></ul><ul><li>} </li></ul><ul><li>} </li></ul>

31. … i.e., Without Regexes <ul><li>$str =~ s/D+/ /g; </li></ul>

32. Nice Formatting, But… <ul><li>if ($month == "1") { $month = "0" . $month; } </li></ul><ul><li>if ($month == "2") { $month = "0" . $month; } </li></ul><ul><li>if ($month == "3") { $month = "0" . $month; } </li></ul><ul><li>if ($month == "4") { $month = "0" . $month; } </li></ul><ul><li>if ($month == "5") { $month = "0" . $month; } </li></ul><ul><li>if ($month == "6") { $month = "0" . $month; } </li></ul><ul><li>if ($month == "7") { $month = "0" . $month; } </li></ul><ul><li>if ($month == "8") { $month = "0" . $month; } </li></ul><ul><li>if ($month == "9") { $month = "0" . $month; } </li></ul>

33. Nice Formatting, But… <ul><li>$month = sprintf "%02d", $month; </li></ul>

34. Too Much Time on Their Hands <ul><li>$smtp->datasend("To: santa.claus@north.polen"); </li></ul><ul><li>$smtp->datasend("From: johnny@homen"); </li></ul><ul><li>$smtp->datasend("Subject: I've Been Goodn"); </li></ul><ul><li>$smtp->datasend("n"); </li></ul><ul><li>$smtp->datasend("Dear Santan"); </li></ul><ul><li>$smtp->datasend("For Christmas I would like:n"); </li></ul><ul><li>$smtp->datasend(" Perl 6n"); </li></ul><ul><li>$smtp->datasend("Thank youn"); </li></ul>

35. Too Much Time on Their Hands <ul><li>$smtp->datasend(<<'EOTEXT'); </li></ul><ul><li>To: santa.claus@north.pole </li></ul><ul><li>From: johnny@home </li></ul><ul><li>Subject: I've Been Good </li></ul><ul><li>Dear Santa </li></ul><ul><li>For Christmas I would like: </li></ul><ul><li>Perl 6 </li></ul><ul><li>Thank you </li></ul><ul><li>EOTEXT </li></ul>

36. Too Much Time on Their Hands <ul><li>$smtp->datasend(<<'EOTEXT' =~ /[^Sn]*(.*?n)/g); </li></ul><ul><li>To: santa.claus@north.pole </li></ul><ul><li>From: johnny@home </li></ul><ul><li>Subject: I've Been Good </li></ul><ul><li>Dear Santa </li></ul><ul><li>For Christmas I would like: </li></ul><ul><li>Perl 6 </li></ul><ul><li>Thank you </li></ul><ul><li>EOTEXT </li></ul>

37. <ul><li>$smtp->datasend(<<'EOTEXT' =~ /[^Sn]*(.*?n)/g); </li></ul><ul><li>EOTEXT </li></ul>Too Much Time on Their Hands To: santa.claus@north.pole From: johnny@home Subject: I've Been Good Dear Santa For Christmas I would like: Perl 6 Thank you <ul><li>Or use, say, Text::Outdent or similar </li></ul>

38. Way Too Much Time On Their hands <ul><li>print "<HTML><HEAD>n"; </li></ul><ul><li>print "<TITLE>My Home Page</TITLE>n"; </li></ul><ul><li>print "</HEAD><BODY>n"; </li></ul><ul><li>print "<H1>My Home Page</H1>n"; </li></ul><ul><li>print "<H2>What I Did Last Summer</H2>n"; </li></ul><ul><li>print "<H3>by Cuthbert J. Bigglesworth</H3>n"; </li></ul><ul><li>print "<P>Me and my dog <I>Fang</I> went down "; </li></ul><ul><li>print "to the river and caught toads.</P>n"; </li></ul><ul><li>print "<P>P.S. I also learned Perl.</P>n"; </li></ul><ul><li>print "<P>Here is a scalar: <KBD>$x</KBD>.</P>n"; </li></ul><ul><li>print "</BODY></HTML>n"; </li></ul><ul><li>Use HTML::Template, Text::Template, the Template Toolkit, or Inline::Files </li></ul>

39. <ul><li>my ($sec, $min, $hour, </li></ul><ul><li>$mday, $mon, $year, </li></ul><ul><li>$wday, $yday, $isdst) </li></ul><ul><li>= localtime(time); </li></ul>The Perils of Cut and Paste # But now use only $mon and $mday...

40. <ul><li>my ($mday, $mon) </li></ul><ul><li>=(localtime)[4,3]; </li></ul>The Perils of Cut and Paste

41. <ul><li>my ($mday, $mon) </li></ul><ul><li>= (localtime)[4,3]; </li></ul>The Perils of Cut and Paste

42. <ul><li>use Time::localtime; </li></ul><ul><li>my ($mday, $mon) </li></ul><ul><li>= (localtime->mday, localtime->mon); </li></ul>The Perils of Cut and Paste

43. Scope? What is This Thing You Call Scope? <ul><li>my ($count, $ncount, @recs, @nrecs, %ccname, %ccphone, %ccaddr, %cccity) </li></ul><ul><li>my ($count2, $temp, @vbinfo, @pscan, $is_true); </li></ul><ul><li>my $temp2; </li></ul><ul><li>my $tempcount; </li></ul><ul><li>my $fudgeFactor; </li></ul><ul><li>my ($fname, $lname, $mi, $address1, $address2, $city, $state, $country, $c_code, $phone, $email, $email_valid); </li></ul><ul><li>my ($form1, $form2, $form3, $form4, $form4a, $form4b, $form4b_valid, @subtotals, $preTaxTotal, $postTaxTotal, $shipping, $TotalTotal); </li></ul><ul><li>my ($is_valid, $discount, $mealpref, $likes_pie, $whatisthisfor); </li></ul><ul><li>my ($PI, $PIE) = (3.14159265358979, "cherry"); </li></ul><ul><li>$count2 = 3; </li></ul><ul><li>[...] </li></ul>

44. Scope Ignorance Cure <ul><li>Move variable declaration to latest possible point </li></ul><ul><ul><li>Exception: configuration settings </li></ul></ul><ul><ul><ul><li>Put those in a separate file if appropriate </li></ul></ul></ul><ul><li>Use in-line declarations for loop variables: </li></ul><ul><ul><li>foreach my $dog (@schnauzers) </li></ul></ul><ul><ul><li>while (my $imp = shift @demons) </li></ul></ul><ul><li>You can carry this even further: </li></ul><ul><ul><li>getopts('dq:v', my %Opt); </li></ul></ul><ul><li>Scope Ignorance is frequently combined with Monolithic Madness </li></ul>

45. Monolithic Madness <ul><li>(Visualize 2500 lines of code without the word 'sub') </li></ul><ul><li>Sufferers’ favorite language: JCL </li></ul><ul><li>“ It started out at 30 lines… it just grew” </li></ul><ul><li>“ I know where everything is” </li></ul><ul><ul><li>Of course, no one else does </li></ul></ul>

46. Monolithic Madness Cure <ul><li>Look for variables with short scopes and evaluate the area for subroutine-ness </li></ul><ul><li>If you like Eclipse, try Devel::Refactor and the extract_subroutine method for the EPIC plug-in </li></ul><ul><li>use strict and turn it off over an ever-narrowing scope: </li></ul><ul><ul><li>use strict; </li></ul></ul><ul><ul><li>[...] </li></ul></ul><ul><ul><li>{ </li></ul></ul><ul><ul><li>no strict; </li></ul></ul><ul><ul><li>[...] </li></ul></ul><ul><ul><li>} </li></ul></ul><ul><ul><li>[...] </li></ul></ul>

47. Perl from ??? <ul><li>$#abspaths = $num; </li></ul><ul><li>for ($i=0; $i<$num; $i++) { </li></ul><ul><li>my $newlen = </li></ul><ul><li>$ROOTLEN+1+length($paths[$i]); </li></ul><ul><li>$abspaths[$i] = ' ' x $newlen; </li></ul><ul><li>$abspaths[$i] = sprintf("%s/%s", $ROOT, </li></ul><ul><li>$dirs[$i]); </li></ul><ul><li>} </li></ul>

48. Perl from C <ul><li>abspaths = realloc(abspaths, </li></ul><ul><li>num * sizeof(char*)); </li></ul><ul><li>for ( i=0; i< num; i++) { </li></ul><ul><li>int newlen = </li></ul><ul><li>ROOTLEN+1+ strlen(paths[ i]); </li></ul><ul><li>char temp[newlen]; </li></ul><ul><li>abspaths[ i] = malloc(newlen); </li></ul><ul><li>sprintf(abspaths[i], "%s/%s", ROOT, </li></ul><ul><li>dirs[ i]); </li></ul><ul><li>} </li></ul>

49. Perl from C <ul><li>@abspaths = map { "$ROOT/$_" } @paths; </li></ul>

50. Perl from ??? <ul><li>$file = "matrix.dat"; </li></ul><ul><li>open (FH, ">$file"); </li></ul><ul><li>for ($I = 1, $I <= 4; $I++) { </li></ul><ul><li>$value = $X[$I][$_], </li></ul><ul><li>write (FH) for 1..10; </li></ul><ul><li>} </li></ul><ul><li>format FH = </li></ul><ul><li><<<<<<<<<<<<< </li></ul><ul><li>$value </li></ul><ul><li>. </li></ul><ul><li>close (FH); </li></ul><ul><li>exit "Done"; </li></ul>

51. Perl from FORTRAN <ul><li>ofile = "matrix.dat" </li></ul><ul><li>OPEN (42, FILE=ofile) </li></ul><ul><li>DO 10 I = 1, 4 </li></ul><ul><li>10 WRITE (42,100) (X(I,J),J=1,10) </li></ul><ul><li>100 FORMAT "(10F10.3)" </li></ul><ul><li>CLOSE (42) </li></ul><ul><li>STOP "Done" </li></ul>

52. Perl from FORTRAN <ul><li>open my $fh, '>', $file or die $!; </li></ul><ul><li>for my $i (1 .. 4) { </li></ul><ul><li>printf {$fh} "%10.3f" $X[$i][$_] </li></ul><ul><li>for 1..10; </li></ul><ul><li>print {$fh} "n"; </li></ul><ul><li>} </li></ul>

53. Perl from ??? <ul><li>###################### </li></ul><ul><li>#Program name: Report. </li></ul><ul><li>###################### </li></ul><ul><li>sub decipher { </li></ul><ul><li>unpack $fmt, shift; </li></ul><ul><li>} </li></ul><ul><li>$fmt = "A7" . # base </li></ul><ul><li>"x4" . # filler </li></ul><ul><li>"A7"; # bonus </li></ul><ul><li>$rec = <>; </li></ul><ul><li>($base, $bonus) = decipher($rec); </li></ul><ul><li>$salary = $base + $bonus; </li></ul><ul><li>printf "%7.2fn", $salary; </li></ul><ul><li>exit; </li></ul>

54. Perl from COBOL <ul><li>IDENTIFICATION DIVISION. </li></ul><ul><li>PROGRAM-ID. Report. </li></ul><ul><li>DATA DIVISION. </li></ul><ul><li>WORKING-STORAGE SECTION. </li></ul><ul><li>01 salary PICTURE 99999V99 </li></ul><ul><li>01 rec </li></ul><ul><li>02 base PICTURE 99999V99 </li></ul><ul><li>02 FILLER PICTURE X(4) </li></ul><ul><li>02 bonus PICTURE 99999V99 </li></ul><ul><li>PROCEDURE DIVISION. </li></ul><ul><li>READ rec </li></ul><ul><li>ADD bonus TO base GIVING salary </li></ul><ul><li>DISPLAY salary </li></ul><ul><li>STOP RUN. </li></ul>

55. Perl from COBOL <ul><li>my $rec = <>; </li></ul><ul><li>my ($bonus, $base) = unpack "A7x4A7", $rec; </li></ul><ul><li>my $salary = $bonus + $base; </li></ul><ul><li>printf "%7.2fn", $salary; </li></ul>

56. Perl from ??? <ul><li>#!/usr/bin/perl -l </li></ul><ul><li>print "Think of a number: "; $dummy = <>; </li></ul><ul><li>$I = 1; </li></ul><ul><li>AGAIN: print "Is it ",$I, "?"; </li></ul><ul><li>$A = <>; </li></ul><ul><li>$X = substr($A,0,1); </li></ul><ul><li>if($X eq"Y" or $X eq"y") { goto DONE } </li></ul><ul><li>$I =$I + 1 </li></ul><ul><li>goto AGAIN; </li></ul><ul><li>DONE: exit; </li></ul><ul><li># END </li></ul>

57. Perl from BASIC <ul><li>100 INPUT "Think of a number: ";D$ </li></ul><ul><li>110 LET I = 1 </li></ul><ul><li>120 PRINT "Is it ", I; </li></ul><ul><li>130 INPUT "?"; A$ </li></ul><ul><li>140 LET X$ = LEFT$(A$,1) </li></ul><ul><li>145 IF X$ = "Y" OR X$ = "y" THEN GOTO 149 </li></ul><ul><li>147 LET I = I + 1 </li></ul><ul><li>148 GOTO 120 </li></ul><ul><li>149 STOP </li></ul><ul><li>150 END </li></ul>

58. Perl from BASIC <ul><li>print "Think of a numbern"; </li></ul><ul><li>my $ans = ''; </li></ul><ul><li>for (my $guess = 1; $ans !~ /^y/i; $guess++) { </li></ul><ul><li>print "Is it $guess? "; </li></ul><ul><li>chomp($ans = <>); </li></ul><ul><li>} </li></ul>

59. <ul><li>read(STDIN, $buffer, $ENV{CONTENT_LENGTH}); </li></ul><ul><li>my @pairs = split(/&/, $buffer); </li></ul><ul><li>push(@pairs, map { split(/&/, $_) } $ENV{QUERY_STRING}); </li></ul><ul><li>push(@pairs, map { split(/&/, $_) } @ARGV); </li></ul><ul><li>foreach my $pair (@pairs) { </li></ul><ul><li>my ($name, $value) = split(/=/, $pair); </li></ul><ul><li>$name =~ tr/+/ /; </li></ul><ul><li>$name =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg; </li></ul><ul><li>$value =~ tr/+/ /; </li></ul><ul><li>$value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg; </li></ul><ul><li>[... You know the rest... ] </li></ul>Cargo Cult Perl <ul><li>Stop the insanity! </li></ul>

60. Cargo Cult Perl use CGI;

61. Comment Code Smells <ul><li>Non-O-O: </li></ul><ul><ul><li>Wannabee Objects and Data Clumps* </li></ul></ul><ul><ul><li>Cut And Paste </li></ul></ul><ul><li>O-O: </li></ul><ul><ul><li>Mixed Abstraction Levels </li></ul></ul><ul><ul><li>Time Dependencies* </li></ul></ul><ul><li>* Courtesy of “The Art of Agile Development”, Shore & Warden </li></ul>

62. Line Editing <ul><li>Reduce bloat </li></ul><ul><ul><li>Mothball code that coverage analysis indicates is not called </li></ul></ul><ul><ul><li>Shorten subroutines and main program to one screen’s length at most </li></ul></ul><ul><ul><li>Don’t exceed screen width </li></ul></ul>

63. Consolidate Variables <ul><li>my (%hits_by_client, %hits_by_method, %hits_by_ext, </li></ul><ul><li>%hits_by_protocol, %hits_by_uri); </li></ul><ul><li>$hits_by_client{$client}++; </li></ul><ul><li>$hits_by_method{$method}++; </li></ul><ul><li>$hits_by_ext{$extension}++; </li></ul><ul><li>$hits_by_protocol{$protocol}++; </li></ul><ul><li>$hits_by_uri{$uri}++; </li></ul>

64. Consolidate Variables <ul><li>my %hits; </li></ul><ul><li>$hits{CLIENT}{$client}++; </li></ul><ul><li>$hits{METHOD}{$method}++; </li></ul><ul><li>$hits{EXTENSION}{$extension}++; </li></ul><ul><li>$hits{PROTOCOL}{$protocol}++; </li></ul><ul><li>$hits{URI}{$uri}++; </li></ul>

65. Consolidate Variables <ul><li>my ($client, $method, $extension, $protocol, $uri) = </li></ul><ul><li>($line =~ /^(S+) - .../); </li></ul><ul><li>my %hits; </li></ul><ul><li>$hits{CLIENT}{$client}++; </li></ul><ul><li>$hits{METHOD}{$method}++; </li></ul><ul><li>$hits{EXTENSION}{$extension}++; </li></ul><ul><li>$hits{PROTOCOL}{$protocol}++; </li></ul><ul><li>$hits{URI}{$uri}++; </li></ul>

66. Consolidate Variables <ul><li>my @KEYS = qw(CLIENT METHOD EXTENSION PROTOCOL URI); </li></ul><ul><li>my %access; </li></ul><ul><li>@access{@KEYS} = ($line =~ /^(S+) - .../); </li></ul><ul><li>my %hits; </li></ul><ul><li>for my $key (@KEYS) { </li></ul><ul><li>$hits{$key}{ $access{$key} }++; </li></ul><ul><li>} </li></ul>

67. Line Editing <ul><li>Remove rote stuff that the computer can figure out for you </li></ul><ul><ul><li>Example: </li></ul></ul><ul><ul><li>$dbh->do("INSERT INTO perf (s, s1a, s1b, x1, x3, y1, y2, y3, zx, zx4, zx4a) VALUES ($s, $s1a, '$s1b', '$x1', $x2, $y1, $y2, $y3, $zx, '$zx4, '$zx4a')"); </li></ul></ul><ul><ul><li>Arrgh </li></ul></ul>

68. Line Editing <ul><li>Try: </li></ul><ul><ul><li>my $sth = $dbh->prepare("INSERT INTO perf (s, s1a, s1b, x1, x3, y1, y2, y3, zx, zx4, zx4a) VALUES (?,?,?,?,?,?,?,?,?,?,?,?)"); </li></ul></ul><ul><ul><li>$sth->execute($s, $s1a, $s1b, $x1, $x3, $y1, $y3, $y2, $zx, $zx4, $zx4a); </li></ul></ul>

69. Line Editing <ul><li>Still too much work, too error-prone. Try: </li></ul><ul><ul><li>$dbh->do( </li></ul></ul><ul><ul><li>make_insert(perf => keys %data), </li></ul></ul><ul><ul><li>undef, values %data); </li></ul></ul><ul><ul><li>sub make_insert </li></ul></ul><ul><ul><li>{ </li></ul></ul><ul><ul><li>my ($table, @cols) = @_; </li></ul></ul><ul><ul><li>"INSERT INTO $table (" </li></ul></ul><ul><ul><li>. join(',' => @cols) . ") VALUES (" </li></ul></ul><ul><ul><li>. join(',' => ('?') x @cols) . ")"; </li></ul></ul><ul><ul><li>} </li></ul></ul>

70. Line Editing <ul><li>This wheel has been invented several times, e.g.: </li></ul><ul><ul><li>use DBIx::Recordset; </li></ul></ul><ul><ul><li># ... </li></ul></ul><ul><ul><li>DBIx::Recordset->insert( { </li></ul></ul><ul><ul><li>'!DataSource' => $dbh, </li></ul></ul><ul><ul><li>'!Table' => 'perf', </li></ul></ul><ul><ul><li>%data } ); </li></ul></ul>

71. Line Editing <ul><li>Get rid of massive strings </li></ul><ul><li>Especially for HTML, use a templating system instead </li></ul><ul><ul><li>HTML::Template works great, even for non-HTML </li></ul></ul><ul><ul><li>So does Text::Template and the Template Toolkit </li></ul></ul>

72. use strict <ul><li>Use it or get sand kicked in your face </li></ul><ul><li>Eliminate all errors in order to get the code to run </li></ul><ul><li>Eliminate unnecessary package variables </li></ul><ul><li>Declare lexical variables explicitly </li></ul><ul><li>Eliminate symbolic references </li></ul><ul><ul><li>They’re hard to maintain anyway and just plain ugly </li></ul></ul><ul><li>Turn strictness off with no strict </li></ul><ul><ul><li>I’ve only ever needed no strict 'refs' </li></ul></ul>

73. use warnings <ul><li>Use it or get sand kicked in your face </li></ul><ul><ul><li>Can use -w instead on older perls </li></ul></ul><ul><ul><li>On newer perls, use -W in testing to force warnings on across all modules </li></ul></ul><ul><li>Leave warnings enabled in production </li></ul><ul><ul><li>But if users might see the warnings, have them sent to you instead </li></ul></ul><ul><ul><li>Trap via $SIG{__WARN__} handler </li></ul></ul>

74. Commonly Neglected Modules <ul><li>Date:: * - look for unnecessary calls to date or cal </li></ul><ul><li>DBI, DBD:: * - look for unnecessary calls to database programs </li></ul><ul><li>LWP:: * - look for unnecessary calls to lynx , wget or GET </li></ul>