Download Scripting - Department of Computer Engineering

Scripting Languages
James Brucker
Computer Engineering Dept
Kasetsart University
Origins
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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
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
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Issue commands to other program(s).
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Shell scripts:
run operating system commands
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Embedded script language:
customize behavior of an application
Example: VBA for MS Office
Lisp for Emacs
Original Unix Script Languages
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/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
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Cygwin: http://www.cygwin.com
MSYS: http://www.mingw.org
DOS "bat" (batch) files are scripts
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Print the <title>...</title> line in all HTML files.
FINDSTR /I /R "<title>.*</title>" *.html
Adding useful message to Batch file
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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
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Perl
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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
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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
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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
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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
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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
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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
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Learn Python: read
http://docs.python.org/tutorial
install Python interpreter on your notebook