osp-ii unit-5

8/2/2019 OSP-II UNIT-5

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Open Source ProgrammingBy

Prof. A. VijayaraniSITEVIT


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Introduction to PERL, TCL& PYTHON

Unit V

Numbers and Strings Control Statements Lists and Arrays Files Pattern matching Hashes Functions. Introduction to TCL/TK,

Introduction to Python.

Open Source ProgrammingAuthor: Prof. A. Vi a arani, Asst. Prof., SITE, VIT


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Introduction to PERLWhat is PERL? Practical Extraction and Report Language Interpreted Language

Optimized for String Manipulation and File I/O Full support for Regular Expressions

RUNNING PERL SCRIPTS - Windows Mode Download ActivePerl and Install it. Put the following in the first line of your script

#!/usr/bin/perl Just run the script from a 'Command Prompt' window as

>perl program_Name.pl



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Basic SyntaxStatements end with semicolon ;

Comments start with #

Only single line comments

Type the program in a text editor. Save it with

the extension of pl

Sample Program#!/usr/bin/perl

print "Hello, world!\n";

Output:Hello, world



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A scalar is the simplest kind of data that Perl manipulates.Most scalars are either a number (like 255 or 3.25e20) or a

string of characters (like hello ).

Dont have to declare a variable before access it.

Don't have to declare a variable's type.

A scalar value can be acted upon with operators (like additionor concatenate), generally yielding a scalar result.

Scalar variable used to store scalar value. It is a casesensitive. It has to start with the symbol $.

Scalars can be read from files and devices, and can be writtenout as well.

Scalars



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Scalars - Numbers

Perl provides different format of numbers like integer,decimal, non-decimal integer (hexadecimal, binary & Octal). Though Perl provides different format, it computes withdouble precision point values.

Sample valid data:

1.25 - decimal255.000 - decimal255.0 - decimal7.25e45 - decimal1234 - integer-40 - integero377 - Octal

ox2AB3 - Hexadecimalob1011 - Binary



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Scalars - Strings

Strings are sequences of characters (like hello). Strings maycontain any combination of any characters.

In a Single quoted( ) string, every thing is interpreted literally.

In a Double quoted( ) string, variables are expanded.

Sample Valid Strings:Hello12 th avenue



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Operations on Numbers

>= -> greater than orequal to

%-> modulo division

-> compare, return 1,0, -1

!= -> not equal to** -> exponent

less than or equalto

/-> division

== -> equal to* -> multiplication

> -> greater than- -> subtraction

< -> less than+ -> addition

Relational OperationsArithmetic

operations

Short hand assignment operators are available in PERL.


Logical

Operators&& - and

|| - or

! - not


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Formatting - Strings

\u converts the first letter into upper case\U converts all characters in a string to upper case

\l - converts the first letter into lower case\L - converts all characters in a string to lower case



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Operations on Strings

1. Concatenation operation . Dot used to concatenate twostrings

$name1 = VIT;$name2 =University;

$name = $name1 . $name2;Print $name; # output VIT University



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2. String repetition - x used to repeat the string for the given

number of times.Example:

$name1 =VIT;$name2 = $name1 x 3;print $name2; # VITVITVIT



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3. Pattern Matching & Replace - Perl provides to match asubstring and replace it with new substring or remove it.

=~ - tests whether a pattern is matched!~ - tests whether patterns is not matched

m used to match a substrings used to substitute a substirngg Global match or substitutei for case insensitive.



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Example

$string = "abc123ddDef";$string =~ s/123/456; # replaces 123 with 456Print $string; # abc456ddDef$string =~ s/456//; # replaces 456Print $string; # abcddDef$string=~s/d/s; # replaces 1st character

print $string; # abcsdDef$string=~s/d/s/g; #replaces all dprint $string; # abcssDef$string =~s/d/s/gi; #replaces all d and Dprint $string; # abcsssefif ($string =~m/b/)

print string contains b;else

print string does not have b;




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I/O StatementsInput: Reading from the standard input stream can be done by. Evaluating this operator in a scalar context gives the nextline of input.

Example:

Print Enter your name;$name = ; #gets input from consolechomp($name); #removes \n in $name

Output: The print operator takes a list of values and sendseach item (as a string, of course) to standard output or to

files.



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Control Statements - IFIf- statement used to take decision and branches the control basedon that.

Syntax:If (condition)

{ true part;}[Else

{false part;}]

Note: it is must, use braces {} for all control statements block

Eg.If ($a>$b)

{print $a, is bigger;}Else

{print $b, is bigger};



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Control Statements - WhileWhile - statement used to repeat set of statements for the givencondition.

Syntax:

While (condition){ statements;}

Eg.while($a


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Control Statements - UntilUntil - statement used to repeat set of statements, if the condition isfalse.

Syntax:

Until (condition){ statements;}

Eg.$a=10;Until ($a >15){print $a; #prints till a reaches value 16$a++;}



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Control Statements - forfor - statement used to repeat set of statements, until meet thegiven condition.

Syntax:

for($i=1;$i


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Control Statements for eachThis statement takes a list of values and assigns them one at a timeto a scalar variable, executing a block of code with each successiveassignment.

Syntax:

foreach $var(list)

{statement;}

Eg:

Foreach $a (10,20,30,40,50){print $a;} #print 10,20,.



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Last Next & Redo Statements Last is similar to break statement of C. Whenever you want toquit from a loop you can use this.

To skip the current loop use the next statement. It immediatelyjumps to the next iteration of the loop.

The redo statement helps in repeating the same iteration again.



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ListList - A list is an ordered collection of scalars.

list name should start with the symbol @.list has the key as numbers. Starts with 0.

An arrayis a variable that contains a list. In Perl, the two terms areoften used as if they are interchangeable. But, to be accurate, thelist is the data, and the array is the variable.

($f, $b, $d) = ("flintstone", "rubble", dad);here $f has flintstone, $b has rubble and $d has dad

Example

@a=(1,2,3,4,5);

@b=(1..5); #same as above ..-range operatorprint @a; #prints all valuesPrint @a[0]; #prints 1st value



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HashesHash - Hashes are like arrays but instead of having numbers as theirindex they can have any strings as index. It should have the values asa pair (key, value).

List name should start with the symbol %.To get a single value from hash, use $hashname{index}.To get all keys, can use Keys(%hashname)To get all values, can use values(%hashname)

Example%a=(name,John,age, 23);print %a; #output - nameJohnage23print $a{name}; # prints JohnPrint keys are, keys(%a); # returns nameage

Print values are,values(%a);#returns John23



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Functions of ListPush and Pop - used to add and remove an element of a listrespectively. Push and pop treat the list variable as a stack andoperate on it. They act on the higher subscript.

Syntax: push(list, value)pop(list)

Example@a=(1,2,3,4,5);Print @a; #prints allPush(@a,12);Print @a;#prints 1,2,3,4,5,12Pop(@a); #removes 12

Print @a; # prints 1,2,3,4,5



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Functions of ListUnshift and Shift - used to add and remove an element of a listrespectively. They act on the lower subscript.

Syntax: unshift(@list, value)shift(@list)

Example@a=(1,2,3,4,5);Print @a; #prints allunshift(@a,12);Print @a;#prints 12,1,2,3,4,5shift(@a); #removes 12Print @a; # prints 1,2,3,4,5



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User Defined FunctionsFunction Declaration: The keyword sub describes thefunction. So the function should start with the keyword sub.

It should be preferably either in the end or in the beginningof the main program to improve readability and also ease indebugging.

E.g.:sub function_name(){ coding }

Function Calling: The symbol & should precede the function name

in any function call.E.g. $v1 = &function_name()



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User Defined FunctionsParameter Passing: Parameter can be passed to the function as a

list . The parameter is taken as a list which is denoted by @_inside

the function. The parameter can be accessed as $_

If only one parameter is passed, the size of @_ list will only be

one.

If two parameters has passed then the @_ size will be two and

the two parameters can be accessed by $_[0],$_[1] ....

More about Parameters & Variables: The variables declared in the main program are by default global

so they will continue to have their values in the function also.

Local variables are declared by putting 'my' while declaring thevariable.



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User Defined FunctionsReturning Values: Return statement used to return a value to the

called program. If no return statement in a function, the result ofthe last operation is returned.

sub fact()

{My $f=1; #local to functionfor ($i=1; $i


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FilesFile Handle: To read and write to files, should create something

called handles which refer to the files.To create the handles, use the OPEN command as follows:

OPEN(filehandleName,filenamewithmode);

E.g.:open(INFILE,"myfile.txt") - reading mode

open(OUTFILE,">myfile.txt") - writing mode indicated by thesymbol >.

open(OUTFILE,">>myfile.txt")- appending mode indicated by thesymbol >>.



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Files - Reading & WritingReading from a File:

$linevalue = ; #reads a line1. The symbol used to read a line from a file pointed by the filehandle1

and that the line is stored in the scalar variable $linevalue.

2. read function is used to read a specific length of information from afile.read(filehandle,$scalarvariable,length)

Writing into a File:print statement is used to write the content into a file.

print filehandle1 $a,$b

Close a File:

Like PHP, close() function used to close a file.close(filehandle)



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Files


Sample Programs

Read File#!/usr/bin/perlopen (fh, "str.pl");$a = ;print $a; #prints the first line$a = ;

print $a; #prints the second line# Reads all line@a = ; #reads all linesprint @a;

#Reads line by line

while($a = ){print $a;}Close(fh);

Write File:#!/usr/bin/perlopen (infile, ">str1.txt");

print "please enter your name";$name = ;print "please enter your id";$id=;#writes data into the file str1.txtprint infile $id, $name;close(infile);


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Files


Sample Programs

Append File

#!/usr/bin/perlopen (infile, ">>str1.txt");#opens in append modeprint "please enter your name";$name = ;print "please enter your id";$id=;print infile $id, $name;close(infile);


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Pattern Matching


* - zero or more times+ - one or more times? - zero or one time^ - beginning of string

$ - end of string. - any character[a-f] - characters a to f[^a-f] - all charactersexcept a to f

{p,q} - at least p times

and at most q times{p,} - at least p times{p} - exactly p times

preg() - used for pattern matching.

Meta characters used for pattern matching:

\b - word boundaries\d - digits\n - newline\r - carriage return\s - white space characters\t - tab\w - alphanumeric characters


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Introduction to TCL/TK


1. Tcl (originally from "Tool Command Language", but conventionallyrendered as "Tcl" rather than "TCL"; pronounced as "tickle" or "tee-see-ell) is a scripting language created by John Ousterhout.

2. Originally "born out of frustration", according to the author, withprogrammers devising their own (poor quality) languages intended to beembedded into applications, Tcl gained acceptance on its own.

3. It is commonly used for rapid prototyping, scripted applications, GUIs

and testing.4. Tcl is used on embedded systems platforms, both in its full form and in

several other small-footprinted versions.

5. Tcl is also used for CGI scripting and as the scripting language for theEggdrop bot. Tcl is popularly used today in many automated testharnesses, both for software and hardware, and has a loyal following inthe Network Testing and SQA communities.

6. The combination of Tcl and the Tk GUI toolkit is referred to as Tcl/Tk.


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Features of TCL/TK

Open Source ProgrammingAuthor: Prof. A. Vijayarani, Asst. Prof., SITE, VIT

1. All operations are commands, including language structures. They arewritten in prefix notation.

2. Commands are commonly variadic.

3. Everything can be dynamically redefined and overridden.

4. All data types can be manipulated as strings, including source code.

5. Event-driven interface to sockets and files. Time-based and user-defined events are also possible.

6. Variable visibility restricted to lexical (static) scope by default, but

uplevel and upvar allowing procs to interact with the enclosing

functions' scopes.


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7. All commands defined by Tcl itself generate error messages on

incorrect usage.

8. Extensibility, via C, C++, Java, and Tcl.

9. Interpreted language using bytecode10. Full Unicode (3.1) support, first released 1999.

11. Cross-platform: Windows API; Unix, Linux, Macintosh, etc.

12. Close integration with windowing (GUI) interface Tk.

13. Multiple distribution mechanisms exist.

Features of TCL/TK



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Introduction to Python


Python is an interpreted, general-purpose high-level programminglanguage whose design philosophy emphasizes code readability.

Python aims to combine "remarkable power with very clear syntax",and its standard library is large and comprehensive.

Its use of indentation for block delimiters is unique among popular

programming languages.


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Features of Python


1. Python is a simple and minimalistic language.2. Python is extremely easy to get started with. Python has an

extraordinarily simple syntax .

3. Python is a Free and Open Source

4. Python is a High-level Language

5. Due to its open-source nature, Python has been ported to manyplatforms

6. Python is interpreted, object oriented and embeddable.


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7. Python is extensible If you need a critical piece of code to runvery fast or want to have some piece of algorithm not to be open,

you can code that part of your program in C or C++ and then usethem from your Python program.

8. Python has extensive libraries. i.e. gives support to do regular

expressions, documentation generation, unit testing, threading,databases, web browsers, CGI, ftp, email, XML, XML-RPC, HTML,WAV files, cryptography, GUI (graphical user interfaces), Tk,

Features of Python



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39pen Source ProgrammingAuthor: Prof. A. Vijayarani, Asst. Prof., SITE, VIT

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