CSCE 606: Scripting Languages and Rapid Prototyping

CSCE 606: Scripting Languages and Rapid Prototyping

What are Scripting Languages?
tr.v. script·ed, script·ing, scripts To prepare (a text) for filming or broadcasting. To orchestrate (behavior or an event, for example) as if writing a script: “the brilliant, charming, judicial moderate scripted by his White House fans” (Ellen Goodman). - 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Scripting Language (cont.)
Programming language that supports scripts - programs written for a special run-time environment that can interpret (rather than compile) and automate the execution of tasks which could alternatively be executed one-by-one by a human operator Can be viewed as a domain-specific language for a particular environment; in the case of scripting an application, this is also known as an extension language High-level language, ~10x less code than system programming language Often implies “small” (≤ few thousand lines of code) Can be domain-specific, e.g. Awk, Sed string processing languages Can be environment-specific, e.g. UNIX Shell, Visual Basic for Applications - 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

CSCE 606 Scripting Languages & Rapid Prototyping
Used for one-time tasks Customizing administrative tasks Simple or repetitive tasks Example: run an application with a sequence of different parameters Extension language LISP in EMACS an early example Controls execution of an application Programmatic interface to graphical application 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Classes of Scripting Web browser – PHP, Javascript,… Extension language – Lua, Tcl, VBA,… GUI – JavaFX, Tcl/Tk,… String processing – Awk, Sed,… OS scripting – Shell, Cshell,… General languages – Perl, Python, Ruby,… Overlap among these 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

System Programming Languages vs. Scripting Languages
C, C++, Java,… Designed for building data structures and algorithms from scratch Concerns: efficiency, expressiveness, strong typing, design support, read-only code, compiled Scripting languages Tcl, Perl, Python, Ruby, Awk, Sed, Shell, Lua,… Designed for gluing components together Concerns: rapid prototyping, typeless, higher level programming, interpreted, code-on-fly 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

System vs. Scripting Languages Uses
System programming languages Component (e.g. library) creation Machine interfaces (e.g. device drivers) Scripting languages Component gluing Use component as a primitive System integration Extension languages 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

System vs. Scripting Language Level
1000 Scripting [Ousterhout 1998] Visual Basic 100 Java Instructions/statement Tcl/Perl C++ C 10 Assembly System programming 1 None Strong Degree of Typing 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Typeless Scripting Facilitates connecting components Variables are containers Usually string-oriented for uniform representation Can generate and then execute code on fly Code is a string Allows code reuse Example: UNIX filter programs read and write byte streams, can create pipelines select | grep scripting | wc select reads text selected on display, grep finds all lines containing “scripting”, wc counts them Can reuse in different situations 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Typing in System Programming Languages
Finds errors at compile-time Permits optimizations But makes it difficult to reuse code Might have to do type conversion Might have to recompile, but may not have source 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Tcl Example button .b –text Hello! –font {Times 16} – command {puts hello} Tcl command creates button control “Hello!” in 16-pt Times on button Prints “hello” when it is clicked Mixes 6 things in one statement: Command name (button) Button control (.b) Property names (-text, -font, -command) Strings (Hello!, hello) Font name (Times 16) Typeface name (Times) Typeface size (16) Tcl script (puts hello) Tcl represents all as strings Arguments can be specified in any order, defaults for >20 unspecified properties 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Tcl Example (cont.) Java - takes 7 lines in 2 methods C++/MFC – 25 lines in 3 procedures Font in MFC: CFont *fontPtr = new CFont(); fontPtr->CreatFont(16, 0, 0, 0, 700, 0, 0, 0, ANSI_CHARSET, OUT_DEFAULT_PRECIS, CLIP_DEFAULT_PRECIS, DEFAULT_QUALITY, DEFAULT_PITCH|FF_DONTCARE, ”Times New Roman”); buttonPtr->SetFont(fontPtr); 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Tcl Example (cont.) Most extra code for strong typing SetFont needs CFont object that must be created and initialized Must call CreateFont to initialize object Has 14 parameters 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Error Checking? Strong typing helps find errors At static analysis/compile time Efficiency – no need for runtime checks Scripting languages check values when used Cannot have font size xyz But must pay cost of runtime checks Must thoroughly test code to find errors 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Interpretation Most scripting languages are “interpreted” This could be “compiled on the fly” or “quickly compile and then execute” for performance Speeds up development loop Flexibility for users to program apps at runtime Example: Tcl interface (extension language) on Synopsys Design Compiler for logic synthesis Generate and execute code on fly E.g. Reformat HTML as Tcl, execute to display page 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Efficiency Scripting languages less efficient Interpretation rather than compilation Run-time “type” checking Power and ease-of-use rather than running on “bare metal” of processor Example Scripting – variable-length string System – binary value in machine word Scripting – hash table System – indexed array 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Is Efficiency an Issue? Usually not Smaller scripted apps Time spent in components, not scripting 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Higher-Level Programming
Scripting statements execute 100s-1000s of machine instructions System PL statements execute ~5 machine instructions Example Perl regular expression substitution as easy as integer addition Tcl variable trace triggers updates when variable set Scripting 5-10x more productivity 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Productivity Application Comparison Code ratio Effort Comments DB app C++: 2 mo Tcl: 1 day 60 Tcl more functionality Comp. sys. test & install C: 272k lines, 120 mo C FIS app: 90k lines, 60 mo Tcl/Perl: 7.7k lines, 8 mo 47 22 DB library C++: 2-3 mo Tcl: 1 wk 8-12 Security scanner C: 3k lines Tcl: 300 lines 10 Display oil well prod. curves C: 3 mo Tcl: 2 wk 6 Tcl version first Query dispatcher C: 1.2k lines, 4-8 wk Tcl: 500 lines, 1 wk 2.5 4-8 Spreadsheet C: 1460 lines Tcl: 380 lines 4 Sim. & GUI Java: 3.4k lines, 3-4 wk Tcl: 1.6k lines, <1 wk 2 3-4 Tcl first, more functionality Code ratio = ratio of #lines of two implementations Effort ratio = ratio of development times [J. K. Ousterhout 1998] 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

System PL Benefits Scripting best for gluing, system integration, extension languages System PL best for complex data structures and algorithms 10-20x faster execution time 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

When to Use Scripting? Is app’s main task to connect preexisting components? Will app manipulate variety of different things? Does app include GUI? Does app do lot of string manipulation? Will app’s functions evolve rapidly over time? Does app need to be extensible? Does app need to be highly portable? 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

When to Use System PL? Does app implement complex data structures or algorithms? Does app manipulate large datasets, so execution speed is critical? Are app’s functions well-defined and slow to change? Are there a small number of target platforms? 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Not Either/Or Most platforms provide scripting and system PL IBM Job Control Language (JCL) - sequence jobs on OS/360 ~1st scripting PL Jobs ran in FORTRAN, PL/1, Algol, COBOL, Assembler UNIX Shell – sh/csh C PC Visual Basic C/C++ Web JavaScript, Perl, Tcl Java 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Why Scripting’s Popularity?
GUIs Often half of development effort Fundamentally gluing components Most scripting had origins in GUI development Internet Gluing Many platforms Component frameworks ActiveX, JavaBeans Manipulate components 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Why Scripting’s Popularity?
Better scripting technology More advanced scripting languages Faster machines Compile-on-fly Garbage collection More casual programmers Quickly learn language “whip up” a script for few-times use E.g. DB queries in spreadsheet Speed of development and use, not execution 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Scripting and OOP Key benefits of OOP Encapsulation – information hiding Interface inheritance – same methods and APIs for different implementations Some OO scripting languages Python, Perl 5+, Object Rexx, Incr Tcl Typeless objects 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Extensibility Many scripting languages provide facility to add to language New commands in Tcl Ruby open classes Key for extension language use Hook scripting language to internals of application components Tk, incr Tcl implemented as Tcl extensions 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Language Comparison Lutz Prechelt, An Empirical Comparison of Seven Programming Languages, IEEE Computer, 2000 C, C++, Java, Tcl, Rexx, Perl, Python 80 implementations of same program Convert phone numbers to mnemonic strings Based on number to string mapping z1000 – 1000 non-empty random phone numbers m1000 – 1000 arbitrary (could be empty) random phone numbers z0 – no phone numbers 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Runtime Dots – individual data value Large dot – median Rectangle – middle half (25-75 percentile) of data |-| - 10 percentile to 90 percentile bounds ---M--- - mean and +/- 1 standard deviation 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Load/Preprocess Dictionary
9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Search Runtime Only 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Memory Consumption 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Program Length 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Programming Time 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Productivity 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Observations People write similar LOC/h Scripting takes 2-3x less code So 2-3x less development time Scripting memory consumption ~higher Java outlier Lot of variation Scripting ~10-20x longer load and preprocess Scripting ~similar search times String-oriented application C/C++ code had more bugs 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Case Study: Pluto System
Swedish pension system Perl connecting Java systems All fund transactions All payments One account per citizen On-line since 2000 Manages $40B+ [Lundborg, Lemonnier 2007, 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

System Details 320k lines Perl 68k lines SQL 27k lines shell script 26k lines HTML 750 GB Oracle DB 500M entries in some tables 5.5M users Daily batch processing 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Used Simple Perl C-like code No advanced Perl constructs Simple run-time type checking code Lots of cross-checking Defensive programming Nothing tricky 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Why Perl? Integrates w/UNIX, Oracle Can focus on algorithms Fast development cycle to cope with changing requirements Remember, a government project! 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

But Hard to read Little typing Poor integration with Java Slow, but not as slow as DB Hard to parallelize (DB server is parallel) 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Type Checking Experience
Most bugs found during unit test Very few type-related crashes in 7 years Typing is maybe better for efficiency (help the compiler) rather than safety 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

What is Rapid Prototyping?
Quick assembly of a partial or complete system for experimentation prior to full requirements, specification and implementation Quick assembly of a tool or system for temporary or permanent use, using special-purpose languages and existing tools Goals Rapid! - <10% of time for traditional C/C++ implementation Functionality – implement functions to permit experimentation or use Okay performance – system only needs to be fast enough to try it out or to be acceptable Easily modified – for iteration during experimentation, or for maintainability 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Relationship to Agile Agile Build system using “final” technology Each iteration is a working system, gradually adding features User stories more than requirements/specs Rapid prototyping May never be a “production” system Need the system to elicit user stories What does user want? “I know it when I see it” – Potter Stewart 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Rapid Prototyping Tools
Shells Bourne shell (sh), C shell (csh), Korn shell (ksh), born-again shell (bash), PowerShell Pattern languages Awk, gawk, sed, grep, perl Extension languages Emacs LISP Scripting languages Tcl, Python, Ruby,… Parser generators Lex, yacc Utilities UNIX: comm, diff, ed, find, sort, uniq, wc Existing tools Reuse, don’t code! 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Tool Characteristics They exist! Lots of needed functionality already built in Avoid coding Quick edit-compile-debug loop Interpreted, compile-on-fly, pre-compiled Simple I/O Mostly just ASCII text, not binary Frequently stream I/O – easier interfacing Easily controlled from other programs Command line interface, extension language, streams, configuration files Often used in combination E.g. awk scripts in a shell script 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Shell Languages Command Interpreters Programming language access to UNIX commands sh, csh are “standard” and portable Applications Need general control constructs File testing, directory access Need functionality of many UNIX tools “Central control” of application Performance Commands dominate runtime, not shell 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Pattern Languages Domain Scan text input, do computation, pass result to output Key Ideas Regular expression matching Multiple matching patterns State machine transformations Conditional expressions Equations Performance Stream/file I/O dominates CPU efficiency less important 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Awk Language Set of <pattern, action> pairs For each input line, execute actions of matching pairs Examples {print $2} – print second field of every line length > 72 {i++} – count # lines > 72 chars END {print i} Applications Good for simple computations on input stream E.g. Take average of a column of numbers 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Sed Language Stream editor Commands are [addr [,addr]] function [args] Apply commands w/matching addresses to each line Can read/write files, test, branch, use buffer space, etc. Buffer size is not infinite Examples sed –e ‘s/ //’ file – delete first 3 spaces of each line sed –e ‘r file1’ file – place contents of file1 between each line Applications Good for local transformations on text streams E.g. capitalize first word of each sentence Most common use is regular expression query-replace 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Grep Language Regular expression pattern search Print all lines that do/do not match pattern grep – limited RE, egrep – full RE, fgrep – fixed strings Example grep ‘^[abc]h’ file – print all lines beginning with “ah”, “bh” or “ch” grep –v ‘Defect’ file – print all lines except those containing “Defect” grep –n foo * - print all lines (w/filename and line number) of all files with “foo” Applications General tool for simple text file searches egrep usually fastest and most general Some may not think of it as a “language” 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Perl Language Practical extraction and report language Combination of awk, sed, sh, csh, etc. functionality C-like syntax, operators, semantics Faster, more powerful than awk,… Features Fast text, binary scan Command line switch parsing Math, system, file testing, I/O control, messaging functions Subroutines Awk (a2p), sed (s2p), find (find2perl) translators Still evolving – Perl 5, Perl 6 (not backward compatible) Applications Facilities management – more secure than C/C++ Networking Web General-purpose For simple things, use awk, sed,… 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Ancient Perl Example Archie Program to access database of useful files available via anonymous FTP Forerunner of Gopher, the forerunner of the Web C version 7889 lines of C code and scripts 1822 lines for VMS operating system support 230 lines for MS DOS support Told you this was an ancient example Perl version 1146 lines of Perl code and scripts Runs on any platform supporting Perl Almost as fast and more reliable 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Extension Languages Tcl General-purpose Small and efficient Easily linked to applications – its original purpose Emacs LISP Write programs to process text Programs to interact with other processes, e.g. shell windows Used to create mail, news group readers, SW development environments Advantages – can watch things happen, capture and replay keystrokes, can run in batch Disadvantages – slow startup time, large memory 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Parser Generators Lex, Yacc Generate lexical analyzer and parser w/C callbacks Many relatives Applications Parse interchange languages of some complexity E.g. HTML, Verilog, VHDL,… Use pattern languages for simple format languages Slow compared to compiled parser 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

UNIX Utilities Think of them as special-purpose tools for program construction Use in combination of not-quite-ideal tools rather than write new one Examples How many words in a word list? #!/bin/csh –f Sort $1 | uniq | wc | awk {print $1} Change files “foo.dat” to “foo.d” foreach i (`ls *.dat`) mv $i {$i:r}.d end Similar on other operating systems 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Existing Tools Use your suite of programs as a toolbox Follow “tool building” and software reuse practices See Software Tools, Kernighan, Plauger, 1976 Identify common needs in multi-person project Parser for common language Display routines Special-purpose widgets Build on your past, recycle, don’t dispose 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Portability Similar tools on different platforms Windows, Apple OS, UNIX/Linux Don’t forget iOS, Android build on Linux Challenge is now GUI, Apple restrictive development environment 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

Conclusions Your first reaction to any new programming tasks should not be to start writing C or C++ For many applications, the prototype is the final system Specifications change a lot, so you want to minimize up-front investment and/or maintenance effort Scripting languages can be used to build systems with existing components Best of both worlds with scripting, system development languages 9/17/2018 CSCE 606 Scripting Languages & Rapid Prototyping

CSCE 606: Scripting Languages and Rapid Prototyping

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