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Introduction to Scripting

Introduction to Scripting. AE 6382. What is a scripting. Scripting is the process of programming using a scripting language A scripting language, like C, Fortran, and Java, has expressions, conditional statements, and loop statements. Unlike C, Fortran, and Java a scripting language has

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Introduction to Scripting

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  1. Introduction to Scripting AE 6382

  2. What is a scripting • Scripting is the process of programming using a scripting language • A scripting language, like C, Fortran, and Java, has expressions, conditional statements, and loop statements. • Unlike C, Fortran, and Java a scripting language has • Loose typing • Interpreted rather than compiled • Usually as some higher level abstractions or built-in functionality

  3. Scripting Features • Scripting languages are generally interpreted rather than compiled • This results in slower execution times compared to a compiled language • C and Fortran are generally fastest • Java is compiled to bytecode that runs on a virtual machine and is slower • The implementation of each individual interpreter varies greatly • Perl, Python, and Ruby are compiled at runtime into an internal format that increases performance • Shell scripts and MATLAB re-evaluate each statement every time • Development cycle is shortened – edit/run

  4. Scripting Features • Scripting languages do not, in general, use strong typing of variables • A variable may during the course of execution contain strings, integers, and objects • Scripting languages frequently build into the basic language higher order abstractions • Text processing • Regular expressions • System interface mechanisms • Most scripting interpreters can be embeddedt into other programs to provide scripting capability within that program • Microsoft Office uses Visual Basic for Applications

  5. Scripting Languages • Simple command/shell scripting, level 1, is the simplest form of scripting • Intended to provide a “batch” execution capability • Unix/Linux • bash, ksh (Korn shell), sh (Bourne shell) • csh (C shell), tsch • These shells can work interactively or in script mode • Have basic programming constructs (if, loops, …) • Windows • cmd/command have no programming constructs • Windows PowerShell (4Q2006) will have extensive scripting based on C# language

  6. Scripting Languages • Limited scripting languages, level 2, have more sophisticated language structure but are limited in their native functionality • No native file I/O capability for example • JavaScript / Jscript / ECMAScript • Available on Unix/Linux and Windows • C based syntax • Used almost exclusively as the client-side scripting language in the various web browsers • Can be used as a system scripting language in Windows via the Windows Scripting Host • Not generally used in Unix/Linux for general purpose scripting • SpiderMonkey is C based JS interpreter • Rhino is Java based JS interpreter

  7. Scripting Languages • VBScript • Available only on Windows, based on Visual Basic for Applications (VBA) • Can be used as the client-side scripting language in Internet Explorer • Most often used with Windows Active Server Pages (ASP) for IIS based web sites • Can be used as a system scripting language in Windows via the Windows Scripting Host

  8. Scripting Languages • Full scripting languages, level 3, have a sophisticated language structure and extensive application support • Perl – Practical Extraction and Reporting Language • A procedure based language with support for objects • Extensive text processing capabilities and regular expressions • Extensible using modules • C based syntax with plethora of symbols • Developed in late 1980’s • Python (also Jython) • An object oriented language with some procedure traits • Extensible • A format based syntax • Developed in early 1990’s

  9. Scripting Languages • Ruby • An object oriented language • Extensible • C like syntax with minimal symbols (no {} () …) • Developed in early 1990’s • TCL – Tool Command Language • A procedural language • Extensible • A stack evaluation syntax, similar to Lisp (lots of []) • Developed as an embeddable scripting language • Developed in late 1980’s

  10. Scripting Languages • Other niche scripting languages • BeanShell • Makes it possible to use Java as a scripting language • REXX • C-like, objects, cross-platform, has a Java version

  11. Perl • General purpose scripting language – Practical Extraction and Reporting Language • Based on the Unix program awk in its early incarnation • Runs everywhere • On Unix/Linux it runs standalone using #! script file convention • On Windows it can run standalone or as an ActiveX scripting engine • Pros • Extensive text processing capabilities including built-in regular expressions • Can be easily extended, there is extensive support for all types of system programming • Has syntax to support object based programming • Most Unix system calls are built-in functions • The built-in system calls will do the right thing in Windows

  12. Perl • Cons • Can be difficult for beginners to learn • Variable naming scheme is initially confusing • There is a high learning curve

  13. Perl • Has 3 classes of variables • $var - scalar (integer, real, string, ...) • @var - array of scalars, $var[0] • %var - hash of scalars, $var{key} • Has local, lexical, and global scoping of variables • Namespace separation • Objects and references are supported • Has the same set of operators as C plus some • Lexical and global scoping of variables • Statements end with ; • Comments are everything after # on a line • Functions sub name { ... }

  14. Perl • Has the same set of operators as C plus some additional • Statements end with ; (semi-colon) • Comments are everything after # on a line • The usual complement of conditional statements • if – then – else (also unless – then – else) • The usual loop statements • for • for each • while • Functions and methods are defined similarly • sub name (…) { … }

  15. Perl • Loop statements for ($i=0 ; $i < 10 ; $i++) { printf “i=%4d\n”,$i; } while (<STDIN>) { print; } @list = (0,5,8,12); foreach $value (@list) { print “Value=$value\n”; } foreach $value (0,5,8,12) { print “Value=$value\n”; } %hash = (part1=>0,part3=>70,part2=>4); foreach $key (sort keys %hash) { print “Value=$hash{$key}\n”; }

  16. Perl • Logical statements if ($i == 1) { print “i=$i\n”; $i++; } unless ($i == 1) { print “Error: i != 1\n”; $i++; } die “Unable to open file” if !open(IN,”filename”); if ($i == 1) { print “Group 1\n”; } else { print “Unknown group\n”; } if ($i == 1) { print “Group 1\n”; } elsif ($i == 2) { print “Group 2\n”; } elsif ($i == 3) { print “Group 3\n”; } else { print “Unknown group\n”; }

  17. Perl • Native Regular Expression Support while (<>) { next if m/.*error.*/; print; } foreach $line (@lines) { next if $line =~ m/^#/; @values = ($line =~ m/.+a=([0-9]+).+c=([0-9]+)/); print “$values[0] $values[1]\n”; } @lines contains (an array of strings): # a b c a=10 b=23 c=16 a=12 b=43 c=17 a=63, b=2, c=999

  18. Perl • Support for objects • use Modulename; (include class definition) • $var = Modulename::new(); (instantiate object) • $var->method(...); (invoke method) • $var->{property}; (access property) • Does not have a class keyword, a class is defined as a Perl module where the functions are invoked as methods and the use of the bless keyword.

  19. Script56.chm is the Windows scripting documentation file Local copy http://www.ae.gatech.edu/classes/ae6382/MS_scripting/ M/S Scripting Documentation

  20. JavaScript / JScript • General purpose scripting language • Usually appears only in web browsers • Available on most platforms • In Windows Jscript is available as an ActiveX scripting engine, when run under the Windows Scripting Host it can functions as a general scripting system • Pros • Its syntax is very much like C • It has support for objects • Cons • Limited availability • Has limited access to host system (security feature)

  21. JavaScript / JScript • Variables • Typeless, refer to primitive types and objects • Can be arrays • Declared with var statement • Uses the usual set of C operators with some additions • Statements are terminated with ; • Comments marked with // and /* ... */ • Functions and methods are declared with function name (...) { ... }

  22. JavaScript / JScript • Loop statements var stdout = WScript.StdOut; var i; for (i=0 ; i < 10 ; i++) { stdout.WriteLine(“i=“+i); } var stdout = WScript.StdOut; var stdin = WScript.StdIn; while (! stdin.AtEndOfStream) { line = stdin.ReadLine() stdout.WriteLine(line); } var stdout = WScript.StdOut; var array = new Array(3); array[0] = 2; array[1] = 12; array[2] = 70; for (var value in array) { stdout.WriteLine("Value: "+array[value]); }

  23. JavaScript / JScript • Logical statements if (i == 5) { stdout.WriteLine(“Equality failed); } if (i == 1) { stdout.WriteLine(“Group 1”); } else { stdout.WriteLine(“Unknown group”); } if (i == 1) { stdout.WriteLine(“Group 1”); } else if (i == 2) { stdout.WriteLine(“Group 2”); } else if (i == 3) { stdout.WriteLine(“Group 3”); } else { stdout.WriteLine(“Unknown group”); }

  24. JavaScript / JScript • Regular Expression Support var stdout = WScript.StdOut; var stdin = WScript.StdIn; var re = new RegExp(".*error.*","i"); while (! stdin.AtEndOfStream) { var line = stdin.ReadLine(); if (line.match(re)) { stdout.WriteLine(line); } }

  25. JavaScript / JScript • Regular Expression Support var stdout = WScript.StdOut; var stdin = WScript.StdIn; var re1 = new RegExp("^#","i"); var re2 = new RegExp(".+a=([0-9]+).+c=([0-9]+)"); var lines = new Array(4); lines[0] = "# a b c"; lines[1] = " a=10 b=23 c=16"; lines[2] = " a=12 b=43 c=17"; lines[3] = " a=63, b=2, c=999"; for (var line in lines) { stdout.WriteLine(lines[line]); if (lines[line].match(re1)) continue; re2.exec(lines[line]); var avalue = RegExp.$1; var cvalue = RegExp.$2; stdout.WriteLine(avalue+", "+cvalue); } // lines contains (an array of strings): // # a b c // a=10 b=23 c=16 // a=12 b=43 c=17 // a=63, b=2, c=999

  26. JavaScript / JScript • Object support • var obj = new Object(); (instantiate object) • obj.method(...); (invoke method) • obj.property; (access property) • obj[“property”]; (access property)

  27. Script56.chm is the Windows scripting documentation file Local copy http://www.ae.gatech.edu/classes/ae6382/MS_scripting/ M/S Scripting Documentation

  28. VBScript • General purpose scripting language • Only available on Windows • Available as an ActiveX scripting engine, when run under the Windows Scripting Host it has general usage • Can be used as the client-side scripting in IE • Pros • Simple syntax (Basic) • Has support for objects • Cons • Windows only

  29. VBScript • Variables • Typeless, refer to primitive types and objects • Can be arrays • Declared with Dim statement • Uses a small subset of C operators • Statements are terminated by the end of line • Comments marked with ‘ (single quote character) • Subroutines Sub name

  30. VBScript • Loop statements Dim i i = 0 For i=0 To 9 Step 1 WScript.StdOut.WriteLine "i=" & i Next Do While Not WScript.StdIn.AtEndOfStream Dim line line = WScript.StdIn.ReadLine() WScript.StdOut.WriteLine(line) Loop Do Until WScript.StdIn.AtEndOfStream Dim line line = WScript.StdIn.ReadLine() WScript.StdOut.WriteLine(line) Loop Dim d 'Create a variable Set d = CreateObject("Scripting.Dictionary") d.Add "0", "Athens" 'Add some keys and items d.Add "1", "Belgrade" d.Add "2", "Cairo" For Each I in d Document.frmForm.Elements(I).Value = D.Item(I) Next

  31. VBScript • Logical statements If i = 5 Then WScript.StdOut.WriteLine “Value is “ & i End If If i = 1 Then WScript.StdOut.WriteLine“Group 1” Else WScript.StdOut.WriteLine “Unknown group” End If If i = 1 Then WScript.StdOut.WriteLine “Group 1” ElseIf i = 2 Then WScript.StdOut.WriteLine “Group 2” ElseIf i = 3 Then WScript.StdOut.WriteLine “Group 3” Else WScript.StdOut.WriteLine “Unknown group” End If

  32. VBScript • Regular Expression Support Dim re Set re = New RegExp re.Pattern = ".*error.*" re.IgnoreCase = True Do While Not WScript.StdIn.AtEndOfStream Dim line line = WScript.StdIn.Readline If re.Test(line) Then WScript.StdOut.WriteLine line End If Loop

  33. VBScript • Regular Expression Support Dim line Dim i Dim match Dim re1, re2, matches, submatches Dim lines(4) lines(0) = "# a b c" lines(1) = " a=10 b=23 c=16" lines(2) = " a=12 b=43 c=17" lines(3) = " a=63, b=2, c=999" set re1 = New RegExp set re2 = New RegExp re1.Pattern = "^#" re2.Pattern = ".+a=([0-9]+).+c=([0-9]+)" For i=0 To 3 line = lines(i) WScript.StdOut.WriteLine "--> " & line If Not re1.Test(line) Then ' WScript.StdOut.WriteLine line Set matches = re2.Execute(line) Set match = matches(0) WScript.StdOut.WriteLine match.SubMatches(0) & ", " & match.SubMatches(1) End If Next ' lines contains (an array of strings): ' # a b c ' a=10 b=23 c=16 ' a=12 b=43 c=17 ' a=63, b=2, c=999

  34. VBScript • Object support • Set obj = New Object (instantiate object) • obj.method(...) (invoke method) • obj.property (access property)

  35. Tcl • General purpose scripting language • Available on most platforms • In Windows it can run standalone an is also available as an ActiveX scripting engine • Pros • Interpreter has a small footprint • Easily embedded • Extensible using C • Cons • Strange syntax

  36. Tcl • Variables • Strings are the basic type • Can create lists and arrays • Uses the expr command to evaluate expressions • Format cmd op op ... op • set var value (set counter 5) • Reference value: $counter (set i $counter) • Use [ ... ] to evaluate immediately

  37. Tcl • Loop statements for (set i 0} {$i < 10} {incr i 3} { lappend aList $i } set aList set i 1 while {$i <= 10} { set product [expr $product * $i] incr i } set product set i 1 foreach value {1 3 5 7 11 13 17 19 23} { set i [expr $i * $value] } set i foreach x [list $a $b [foo]] { puts stdout “x = $x” }

  38. Tcl • Logical statements if {$i == 5} { puts stdout “Equality failed” } if {i == 1} { puts stdout “Group 1” } else { puts stdout “Unknown group” } if {i == 1} { puts tdout “Group 1” } elseif (i == 2) { puts tdout “Group 2” } elseif (i == 3) { puts stdout “Group 3” } else { puts stdout “Unknown group” }

  39. Tcl • Logical statements if {$x == 0} { puts stderr “Divide by zero” if (i == 1) { stdout.WriteLine(“Group 1”); } else { stdout.WriteLine(“Unknown group)”; } if (i == 1) { stdout.WriteLine(“Group 1”); } else if (i == 2) { stdout.WriteLine(“Group 2”); } else if (i == 3) { stdout.WriteLine(“Group 3”); } else { stdout.WriteLine(“Unknown group”); }

  40. Python • General purpose scripting language • Available on most platforms • On Unix/Linux it runs standalone using #! script file convention • In Windows it can run standalone an is also available as an ActiveX scripting engine • Designed from the start as an object oriented language • Pros • Has wide support and runs everywhere • Jython is a version coded in Java and can access Java classes directly • Cons • Has a syntax based on formatting

  41. Python • Variables • Typeless • Scalar name = “sam” • Lists names = [“sam”, “bill”, “ted”] • Tuples (1,2,5,20) • Dictionaries rooms = {“sam”:302,”bill”:305,”ted”:401} • Namespace separation (packages) • Block structure is indicated by spacing • Strings are immutable

  42. Python • Loop statements Count = 0 for line in range(0..10): count = count + 1 print count Count = 10 While count < 10: count = count + 1

  43. Python • Conditional statements Value = 2 if value%2 == 0: print “Value is even” else: print “Value is odd”

  44. Python • Object support • Class definition • Object instantiation • obj = Special() • Method invocation • obj.method1(…) class Special: def __init__(self): self.count = 0 def method1(self,…): … def method2(self,…): …

  45. Ruby • General purpose scripting language • Available on most platforms • On Unix/Linux it runs standalone using #! script file convention • Designed from the start as an object oriented language • Pros • Is becoming widely used • Has a more conventional syntax without the clutter of C and Perl • Cons • Is relatively new on scene

  46. Ruby • Variables • Typeless • $global_variable • @@class_variable • @instance_variable • local_variable • Types of variables • Scalar name = “sam” • Arrays names = [“sam”, “bill”, “ted”], names[2] • Hashes rooms = {“sam”:302,”bill”:305,”ted”:401}, rooms{“sam} • Namespace separation

  47. Ruby • Loop statements count = 1 while count < 10 count = count + 1 end count = 1 until count == 10 count = count + 1 end loop count = count + 1 end count = 1 begin count = count + 1 end while count < 10 count = 1 begin count = count + 1 end until count == 10

  48. Ruby • Conditional statements value = 6 if value%3 == 0 print “remainder 0” elsif value%3 == 1 print “remainder 1” else print “remainder 2” end value = 6 unless value == 6 print “value is not 6 end print “stop” if value == 0

  49. Ruby • Object support • Class definition • Object instantiation • obj = special.new • Method invocation • obj.method1(…) class special def initialize … end def method1(…) … end def method2(…) … end end

  50. Scripting in Unix • The usual method of executing a script in Unix/Linux is to include the location of the interpreter on line 1 • #!/usr/bin/perl • #!/usr/bin/sh • The script must be readable and executable by the user attempting to run it

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