Scripting Languages

James Brucker

Computer Engineering Dept

Kasetsart University

Origins

Used to create a list of commands for the operating system to execute.

Automate repetative tasks.

# Delete all files in the /tmp directory that

# have not been used in 7 days.

find /tmp -atime +7 -type f -exec rm { } \;

File: cleantemp.sh

shell> cleantemp.sh

And the script grows...

# Delete all files in the /tmp and /var/tmp that

# have not been used in 7 days.

find /tmp -atime +7 -type f -exec rm { } \;

find /var/tmp -atime +7 -type f -exec rm { } \;

# Delete all files in several directories

# have not been used in 7 days.

DIRS="/tmp /var/tmp /var/spool/mqueue"

for d in $DIRS; do

find $d -atime +7 -type f -exec rm { } \;

done

Characteristics of Scripts

Issue commands to other program(s).

Shell scripts: run operating system commands

Embedded script language: customize behavior of an applicationExample: VBA for MS Office Lisp for Emacs

Original Unix Script Languages

/bin/sh – Bourne shell /bin/bash – Bourne-again shell /bin/csh – C-shell (syntax is like C)

Using helper commands: grep - find strings in files sed - stream editor find - search for files dirname, filename

Unix Toolkits for Windows

Cygwin: http://www.cygwin.com MSYS: http://www.mingw.org

DOS "bat" (batch) files are scripts

Print the <title>...</title> line in all HTML files.

FINDSTR /I /R "<title>.*</title>" *.html

Adding useful message to Batch file

Print help if no parameters given Print a message if no matching files.

@ECHO OFF

IF "x%1" == "x" (

@ECHO Usage: showtitles filespac [...]

GOTO END

)

FINDSTR /I /R "<title>.*</title>" %*

IF ERRORLEVEL 1 @ECHO No match found

:END

Exercise

Write a BAT file to find all occurrences of a given HTML tag.

Example: findtags h1

Perl

Practical Extraction and Reporting Language Originally for systems admin work on Unix Often used for "CGI" web applications Excellent text processing (regex) support Extensive libraries: CPAN network

Disadvantages almost no type checking scripts can be difficult to read not built on O-O foundation

Perl: download and save a URL

Download a URL from the web and save it to a local file... without using a web browser!

Prerequisite: install LWP module

shell> cpan install LWP

Perl: download and save a URL

uses LWP getstore( url, filename) function

#!/usr/bin/perl# Download a URL and save as a fileuse LWP::Simple;

# get filename from URL$url = $ARGV[0];if ( $url =~ /.*\/([^\/]+)$/ ) { $file = $1; }else { $file = "noname.html"; }

$rc = getstore( $url, $file);

if ( is_success( $rc ) ) { print "URL saved as $file\n"; }else { print "Failed. HTTP response code $rc\n"; }

Python: an O-O language

Designed as O-O language Supports many common data structures Good C API Named after Monty Python Libraries almost as extensive as Perl

Disadvantages uses indentation to denote blocks & scope unusual syntax

Python: download a URL

#!/usr/bin/pythonimport urllibimport sys

if (len(sys.argv) < 2): print "Missing URL name\n" sys.exit(-1)

# get a handle for URLurl = urllib.urlopen( sys.argv[1] )# open output filef = open("somefile.html", "w")f.write( url.read() )f.close()url.close( )

Python: define a class

class Person:# constructordef __init__(self, name):

salf.name = name

# greet the persondef greet(self):

print "Hello " + self.name

#end of the classsanta = Person("Santa Claus")santa.greet()# get data type - like Java getClass( ) methodprint type( santa )

Ruby and Rails

Modern script language with many ideas from Perl

Completely O-O Killer app: Rails web framework

Disadvantages slow weird syntax and multiple commands to do

same thing

Ruby: 4 ways to join strings

s = "hello " "world"t = "hello " + " world"u = "hello ".concat(" world")v = "hello " << " world"print sprint(t) # parenthesis are optional

Groovy

Interpreted language based on Java syntax Can import and use any Java class Groovy compiler (groovyc) generates

Java .class files! Killer app: Grails web framework

Assignment

Learn Python: readhttp://docs.python.org/tutorial

install Python interpreter on your notebook