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Scripting Languages

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. File : cleantemp.sh. # Delete all files in the /tmp directory that

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Scripting Languages

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  1. Scripting Languages James Brucker Computer Engineering Dept Kasetsart University

  2. Origins • Used to create a list of commands for the operating system to execute. • Automate repetative tasks. File: cleantemp.sh # Delete all files in the /tmp directory that # have not been used in 7 days. find /tmp -atime +7 -type f -exec rm { } \; shell> cleantemp.sh

  3. 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

  4. 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

  5. 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

  6. Unix Toolkits for Windows • Cygwin: http://www.cygwin.com • MSYS: http://www.mingw.org

  7. DOS "bat" (batch) files are scripts • Print the <title>...</title> line in all HTML files. FINDSTR /I /R "<title>.*</title>" *.html

  8. 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

  9. Exercise • Write a BAT file to find all occurrences of a given HTML tag. Example: findtags h1

  10. 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

  11. 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

  12. Perl: download and save a URL • uses LWP getstore( url, filename) function #!/usr/bin/perl # Download a URL and save as a file use 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"; }

  13. 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

  14. Python: download a URL #!/usr/bin/python import urllib import sys if (len(sys.argv) < 2): print "Missing URL name\n" sys.exit(-1) # get a handle for URL url = urllib.urlopen( sys.argv[1] ) # open output file f = open("somefile.html", "w") f.write( url.read() ) f.close() url.close( )

  15. Python: define a class class Person: # constructor def __init__(self, name): salf.name = name # greet the person def greet(self): print "Hello " + self.name #end of the class santa = Person("Santa Claus") santa.greet() # get data type - like Java getClass( ) method print type( santa )

  16. 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

  17. Ruby: 4 ways to join strings s = "hello " "world" t = "hello " + " world" u = "hello ".concat(" world") v = "hello " << " world" print s print(t) # parenthesis are optional

  18. 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

  19. Assignment • Learn Python: readhttp://docs.python.org/tutorial • install Python interpreter on your notebook

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