Perl: Programming Freedom Fundamentals of Engineering For Honors – H192Perl: Programming FreedomPractical Extraction and Report LanguagePractical? Report? This doesn’t have to do with labs, does it?Perl vs. C: Major DistinctionsPerl vs. C: Syntax and OperatorsPerl Data Types: Scalars ($)Scalar Example With Some TwistsPerl Regular Expressionsexample: $str =~ m/a*b?+d/ matches 0 or more “a”s (e.g., “”, “a”, “aa”, etc.) followed by 0 or 1 “b”s (e.g., “”, “b”) followed by a literal “+” (the backslash escapes the “+”) followed by 1 digit 0-9 (d – (d)igit) example: “12345” =~ m/d(d)d(d)d/ sets $1 to “2” (first set of parentheses) sets $2 to “4” (second set of parentheses) example: “12345” =~ m/(d(d)d)dd/ sets $1 to “123” (first set of parentheses) sets $2 to “2” (second set of parentheses)Perl Regular Expression ExamplePerl I/OPerl File I/OPerl File I/O ExampleLearn more than one language? That’s dumb even for a geek.Please End; Really, Leave!Lecture 10APerl: Programming FreedomFundamentals of Engineering For Honors – H192By Robert Mohr,Ted Pavlic, andJoe RyanLecture 10APerl: Programming FreedomWhat is Perl?Why should I use Perl?What does Perl look like? Show me some examples.ConclusionLecture 10APractical Extraction and Report LanguageDebuted on December 18, 1987 (Ted was 6)Invented by Larry Wall–Linguist and Computer ScientistProgramming Perl: 3rd Edition–The essential book on Perl–http://www.ora.com/ (O’Reilly)CS&E 459.51–1 Credit Hour Spring S/U Course on Perl at OSUhttp://www.perl.org/http://www.cpan.org/Lecture 10APractical? Report? This doesn’t have to do with labs, does it?Originally meant to be a glue language–Many applications, many platforms, many files, much power . . . With no way to communicateNeed for a general purpose tool with a strong ability for text processing and reportingText Processing? World Wide Web? How could those two possibly relate?!The embodiment of computational synergy?Lecture 10APerl vs. C: Major DistinctionsPerl is interpreted, C is compiled.Negatives:–Perl requires additional overhead (CPU time, memory, etc.)–Perl code is slower than C, all other things being equalPositives:–Perl is easier to extend & upgrade without recompiling–Perl is not platform-specific, but C is–Perl implements powerful features without needing new architecture–Perl is constantly growing; powerful modules can be easily added–Perl has major security features as part of the language–Perl is great for rapid prototypingLecture 10APerl vs. C: Syntax and OperatorsBorrows syntax from C, awk, BASIC, Python, Pascal, English, Greek–Extremely familiar, comfortable, and unconventionalFlexible operators and constructs–do, for, while, ==, =, <, >, ++, --, +, -, *, /, !, &&, ||–foreach, unless, until, =~, eq, ne, and, or, not (and more…)Loosely-typed variables and automatic conversionsBuilt-in text string comparison, parsing, pattern-matchingSimple I/O libraryHundreds of pre-written modules extend Perl for many tasks –(CPAN: http://www.cpan.org/)Easy object-oriented programmingLecture 10APerl Data Types: Scalars ($)Scalars store numeric and string data (and more!)Syntax: $scalar_nameAutomatic conversion between numeric and text data types when appropriate$x = 5;$y = -6.7;$z = “foo”;$a = $x + $y; # $a == -1.7$b = $z . $x; # $b eq “foo5”$t = “hello” x 5; # $t eq “hellohellohellohellohello”$g = $x ** 2; # exponentiation – $g == 25Lecture 10AScalar Example With Some Twists# Declare and initialize some scalars to play with$w = 1; $x = 2; $y = “2”; $z = “4.5”; $s = “text”;If (1 == $w) { print “w = 1\t”; } # Compare scalar & constantprint “x = y = $x\t” if ($x == $y); # Compare two scalars# Notice placement of ifwhile($z > $y) { $z--; } # while / decrement scalarprint( “z = $z\n” ); # Print scalar valueprint “Of course $z isn’t the same as $s!\n”if ($z ne $s); # String “not-equal” compareOutputw = 1 x = y = 2 z = 1.5Of course 1.5 isn’t the same as text!Lecture 10APerl Regular Expressionsallow for matching strings against patternsspecial characters–. matches any character–* matches 0 or more of the preceding character–? matches 0 or 1 of the preceding character–+ matches 1 or more of the preceding characterescape sequences–\d matches any (d)igit–\s matches any white(s)pace (tab “\t”, space “ ”, newline “\n”)–\w matches any alphanumeric “(w)ord” charactercapturing–parentheses in the pattern (e.g., m/(\d)\d/) cause the portion of the string in the parentheses to be captured into a temporary variableLecture 10Aexample: $str =~ m/a*b?\+\d/ matches–0 or more “a”s (e.g., “”, “a”, “aa”, etc.) followed by–0 or 1 “b”s (e.g., “”, “b”) followed by –a literal “+” (the backslash escapes the “+”) followed by–1 digit 0-9 (\d – (d)igit)example: “12345” =~ m/\d(\d)\d(\d)\d/ –sets $1 to “2” (first set of parentheses) –sets $2 to “4” (second set of parentheses)example: “12345” =~ m/(\d(\d)\d)\d\d/ –sets $1 to “123” (first set of parentheses) –sets $2 to “2” (second set of parentheses) Perl Regular Expression UsageLecture 10APerl Regular Expression Example# Declare and initialize some arrays of famous people’s namesfor my $prof (“Dr. Demel”, “Dr. Freuler”, “Mr. Clingan”){if ( $prof =~ m/Dr\. (.*)/){print $1,” has a PhD\n”;}}Lecture 10APerl I/OPrint to standard output (screen)–print “text”;print $scalar;print @list; print STDOUT “text”;Read from standard input (keyboard)–$line = <STDIN>;chomp $line;The angle operator (<>) (used very frequently!)–chomp( $line = <> );Lecture 10APerl File I/OOpen a file–open(IN, “filename”); # Open for readingopen(OUT, “>filename”); # Open for writingopen(OUT, “>>filename”); # Open for appendingInput from file referenced by the handle “IN”–$line = <IN>;Print to the file referenced by the handle “OUT”–print OUT “text”;Close a file–close IN;close OUT;Lecture 10APerl File I/O Exampleprint “Enter file to read: “; # Ask user for a filename$filename = <STDIN>; # Retrieve entire linechomp $filename; # Get rid of ‘\n’ if thereopen(IN, $filename); # Open the files (notice fileopen(OUT, “>example.out”); # descriptors IN and