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 application Example: 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: MSYS:

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

Adding useful message to Batch file Print help if no parameters given Print a message if no matching OFF IF "x%1" == "x" Usage: showtitles filespac [...] GOTO END ) FINDSTR /I /R ".* " %* IF ERRORLEVEL 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 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"; }

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/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( )

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 )

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 s print(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: read install Python interpreter on your notebook