Perl, A Hardware Language

8/2/2019 Perl, A Hardware Language

1/53

PerlA Scripting language

Larry Wall


2/53

ProgrammingWhat does an Engineer need?

Occasionally, an Engineer will have to write aprogram!

What types of problems might require

programming?

Generate complex data streams as input to another

problem

Parse/collect information out of large data files

Write a program that runs other programs in a

regression test


3/53

Many programs are throw away code use once to

complete a task, then forget about it.

Need to become very familiar with a favorite

programming language, and use it enough to

become time efficient.

Convert data files from one format to another


4/53

Desirable Features of a Programming

Language for throw-away code

Powerful get a lot done with a little code

Flexible be able to do many different types of

tasks

GUIs, string processing, program control,number crunching , etc.

Well documented

Large user base so external libraries, examples

readily available


5/53

Portable be able to run on different systems

Readily available (free is the best!)


6/53

C, C++, Fortran are traditional compiled languages

Pros

High performance code

Portable between systems

Free C, C++, Fortran compilers from the FreeSoftware Foundation


7/53

Cons

Usually have to write a lot of code to get even simple

tasks done

Must compile source code first on target system

before execution.

GUI interfaces are Operating System dependent

Support for scripting (i.e, controlled execution of

other programs) is minimal and Operating Systemdependent

Best for large, complex tasks -- but may not be best

choice for simple tasks (i.e, < 100 lines of code)


8/53

UNIX Shell Scripting Languages

All UNIX shells (csh, bash, ksh, etc) support a

scripting language

Pros

Built in to shell, always available for useIdeal for scripting duties (control of other programs)

Cons

Fairly primitive features, no powerful operators or

data handling featuresVery slowat least 100x slower than compiled code

No GUI capabilities

Only useful for Unix applications


9/53

Java Portable object-oriented programming language

ProsPowerful data structures, functions

Portable between Unix/Windows

Free development environment

Powerful GUI buildingUseful for Web page enhancement

Decent performance (about 10x less than compiled

C/C++)

ConsLimited scripting, string processing

Object-oriented programming model is possible

overkill for simple throw-away programs


10/53

Now coming to Perl


11/53

OUTLINE

Introduction

The start of Perl

Perl overview

Regular expression

Example: Automatic batch execution


12/53

INTRODUCTION

Perl Practical Extract & Report Language

Created by Larry Wall

Fill in the gap between the high level languageand the low level language

High Level Language

(Ex: Shell)Low Level Language

(Ex: C, C++)Perl


13/53

WHATCAN PERLDO?

Suitable for a quick-and-dirty program Ex: File parser

30%~70% of the size of the equivalent C

program

Powerful in process of strings Pattern matching and regular expression


14/53

WHATCAN PERLDO? (CONTI.)

b9.vC432.valu2.v

b9_t.vC432_t.valu2_t.v

Perl

>verilog b9.v b9_t.v > b9.rlt>verilog C432.v C432_t.v > C432.rlt>verilog alu2.v alu2_t.v > alu2.rlt

Automatic batch execution

Designs

Testbenchs

Automatic execution


15/53

15

WHATCAN PERLDO? (CONTI.)

module alu2(a, b, c)input a;input b;..endmodule

Point Incr Path---------------------------------------------------input external delay 0.0000 0.0000

fa (in) 0.0000 0.0000 fvlg_inst1/Y (NAND2XL) 0.0478

0.0478 r

c (out) 0.0000 0.1115 rdata arrival time 0.1115

module top_tb;

alu2 a1(input[0], input[1],);

#1.1115; clk = 1; input =`INPUT_NUM'bx;

#1.1115; clk = 0; input =inputVector;

endmodule

Perl

Design (.v)

Timing report by Synopsys (.timing)

Testbench (.v)


16/53

THESTARTOF PERL

#! /usr/bin/perl

print Hello World;

int main(int argc, char* argv[]){

printf( Hello World);

return 0;

}

A simple program: Hello world!


17/53

PERLOVERVIEW

Similar to C

Basic overview:

Variables Useful data structures

Array

Hash Control structures


18/53

VARIABLES

Can store string and value

$number; (in Perl)

int number;

float number;

char number[50];

strcpy (number, Alex); (in C)

$number = Alex; (in Perl)

Dont need to declare variables before use them


19/53

STRINGORNUMERIC ?

Identified by operator Numeric operators: < + >, < - >, < * >, < />

String operators: < . >, < x >, < eq >

hello . world =

helloworld

hello x 3 = hellohellohello

helloeqhello => true

Ex:

$numA = 10, $numB = 12$numA + $numB = 22

$numA . $numB = 1022


20/53

LIST & ARRAY

List: the union of data Ex: (11, hello, 12)

Array: the variable where stores a list

Ex: $myArray[0] == 11

$myArray[1] == hello$myArray[2] == 12

@myArray == ( 11, hello, 12)

myArray

11

hello

12

0

1

2


21/53

CONTEXT

Scalar context: $numA == 1, $numB == 2

$numA + $numB = 3 > Scalar context

List context:

@people ==(11, hello, 12)@abc = @people > List context

print @abc; # 11 hello 12


22/53

HASH

$hash_variable{$some_key} Ex: $myHash{foo} = 11;

$myHash{25.4} = hello;

print $myHash{foo} # 11

%hash_var = (key, value, key, value,)

%myHash = (foo, 11, 25.4, hello)

myHash

11

hello

foo

25.4


23/53

Operators

Perl uses all the usual C arithmetic operators:$a = 1 + 2; # Add 1 and 2 and store in $a$a = 3 - 4; # Subtract 4 from 3 and store in $a$a = 5 * 6; # Multiply 5 and 6

$a = 7 / 8; # Divide 7 by 8 to give 0.875$a = 9 ** 10; # Nine to the power of 10$a = 5 % 2; # Remainder of 5 divided by 2++$a; # Increment $a and then return it

$a++; # Return $a and then increment it--$a; # Decrement $a and then return it$a--; #Return $a and then decrement it


24/53

and for strings Perl has the following among

others:$a = $b . $c; # Concatenate $b and $c$a = $b x $c; # $b repeated $c times


25/53

Assigning Perl Values

To assign values Perl includes

$a = $b; # Assign $b to $a$a += $b; # Add $b to $a$a -= $b; # Subtract $b from $a$a .= $b; # Append $b onto $a ($a, $b

contain strings)

Note that when Perl assigns a value with$a = $b it makes a copy of $b and then assigns thatto $a. Therefore the next time you change $b it willnot alter $a.


26/53

Interpolation of Variable Names

The following code prints apples and pears using

concatenation (note the use ofthe . (period) as thestring concatenation operator).

$a = 'apples';$b = 'pears';print $a . ' and ' . $b;

It would be nicer to include only one string in thefinal print statement, but the line

print '$a and $b';

prints literally $a and $b which isn't very helpful. Insteadwe can use double quotesin place of the single quotes:


27/53

print "$a and $b";

The double quotes force interpolation of any codes,

including interpretingvariables. Other codes that areinterpolated include special characters such asnewline and tab. The code\n is a newline and \t isa tab.


28/53

Array Variables

A slightly more interesting kind of variable is thearray variable which is a listof scalars (i.e numbersand strings). Array variables have the same format asscalar variables except that they are prefixed by an @

symbol. The statement

@food = ("apples", "pears", "eels");@music = ("whistle", "flute");

assigns a three element list to the array variable @foodand a two element list to the array variable @music.


29/53

The array is accessed by using indices starting from 0,and square brackets are used to specify the index. The

expression

$food[2]

returns eels. Notice that the@ has changed to a $because eels is a scalar.


30/53

Array Assignments

As in all of Perl, the same expression in a differentcontext can produce a different result. The firstassignment below explodes the @music variable sothat it is equivalent to the second assignment.

@moremusic = ("organ", @music, "harp");@moremusic = ("organ", "whistle", "flute", "harp");

This should suggest a way of adding elements to anarray. A neater way of adding elements is to use thestatement

push(@food, "eggs");


31/53

which pushes eggs onto the end of the array @food. Topush two or more itemsonto the array use one of thefollowing forms:

push(@food, "eggs", "lard");

push(@food, ("eggs", "lard"));push(@food, @morefood);

The push function returns the length of the new list.


32/53

More List Manipulation

@food = ("eels", "lard", "bread" );

It is possible to assign an array to a scalar variable.

Examples are:$f = @food; # $f = length of @food, here = 3.$g = $#food; # $g = last index of @food, here = 2

The assignment:$f = @food;

turns the value of $f into a string that are the members of@food with a space between each element.


33/53

The assignment below assigns $g the last item in the

list @food:$g = $food[$#food]; # $g = $food[2] = bread;

To remove the last item from a list and return it use thepop function. Note that after this assignment, $g =bread, and @food only has 2 elements left.

$g = pop(@food);


34/53

File Handling

Here is a simple perl program which does the same asthe UNIX cat command on a certain file.

#!/usr/bin/perl#

# Program to open the password file,read it in,# print it, and close it again.

$file = '/etc/passwd'; # Name the fileopen(INFO, $file); # Open the file@lines = ; # Read it into an arrayclose(INFO); # Close the file

print @lines; # Print the array


35/53

More File Handling

The open statement can also specify a file for

output and for appending as well as for input. Todo this, prefix the filenamewith a > for output and a >> for appending:

open(INFO, $file); # Open for inputopen(INFO, ">$file"); # read onlyopen(INFO, ">>$file"); # appendingopen(INFO, "


36/53

To open the standard input (usually the keyboard) and

standard output (usually the screen) respectively do:

open(INFO, '-'); # Open standard input

open(INFO, '>-'); # Open standard output


37/53

foreach Control Structure

To go through each line of an array or other list-like

structure (such as lines in a file) Perl uses theforeach structure. This has the form:foreach $morsel (@food) # Visit each item in

turn# and call it $morsel

{print "$morsel\n"; # Print the item

print "Yum yum\n"; # That was nice}


38/53

Testing

The next few structures rely on a test being true orfalse. In Perl any non-zero number and non-emptystring is counted as true. The number zero, zero byitself in a string, and the empty string are counted as

false. Here are some tests on numbers and strings.

a == $b # Is $a numerically equal to $b?

# Beware: Don't use the = operator.$a != $b # Is $a numerically unequal to $b?$a eq $b # Is $a string-equal to $b?$a ne $b # Is $a string-unequal to $b?


39/53

You can also use logical and, or and not:

($a && $b) # Is $a and $b true?($a || $b) # Is either $a or $b true?!($a) # is $a false?


40/53

for Control Structure

Perl has a for structure that mimics that of C. Ithas the formfor (initialise; test; inc){

first_action;second_action;etc }

First of all the statement initialise is executed. Thenwhile test is true the blockof actions is executed. Aftereach time the block is executed inc takes place. Here isan example for loop to print out the numbers 0 to 9.


41/53

for ($i = 0; $i < 10; $i++) # Start with $i = 0# Do it while $i < 10# Increment $i before

repeating{

print "$i\n";

}


42/53

while

Here is a program that reads some input from thekeyboard and won't continue until it gets the correctpassword

#!/usr/bin/perl

print "Password? "; # Ask for input$a = ; # Get inputchop $a; # Remove the newline at endwhile ($a ne "fred") # While input is wrong...

{print "sorry. Again? "; # Ask again$a = ; # Get input againchop $a; # Chop off newline again

}


43/53

do - untilHere is a version of the previous program that uses ado until control structure:#!/usr/local/bin/perldo{

"Password? "; # Ask for input$a = ; # Get input chop$a; # Chop off newline}

while ($a ne "fred") # Redo while wrong input


44/53

if, elsif statements

Of course Perl also allows if/then/else statements.These are of the following form:

if ($a) {

print "The string is not empty\n";} else {

print "The string is empty\n";}


45/53

Regular Expressions

A regular expression is contained in slashes, andmatching occurs with the =~ operator. The followingexpression is true if the string the appears in variable$ sentence.

$sentence =~ /the/

The RE is case sensitive, so if $sentence = "Thequick brown fox"; then the above match will be

false. The operator !~ is used for spotting anonmatch. In the above example

$sentence !~ /the/

is true because the string the does not appear in $sentence.


46/53

SubroutinesPerl allows the user to define their own functions,

called subroutines. Theymay be placed anywhere inyour program but it's probably best to put them all atthe beginning or all at the end. A subroutine has theform

sub mysubroutine {print "Not a very interesting routine\n";print "This does the same thing every time\n";}The above subroutine ignores any parameters passed to it. All of thefollowing will work to call this subroutine. Notice that a subroutine is calledwith an & character in front of the name:&mysubroutine; # Call the subroutine&mysubroutine($_); # Call it with a parameter&mysubroutine(1+2, $_); # Call it with two parameters


47/53

Passing Parameters to Subroutines

When a subroutine is called any parameters are passed

as a list in the special@_ list array variable. Thefollowing subroutine merely prints out the list that itwas called with. It is followed by a couple of examples ofits use.

sub printargs {print "@_\n";

}&printargs("perly", "king"); # Example prints

"perly king"&printargs("frog", "and", "toad"); # Prints

"frog and toad"


48/53

Pros

Powerful data structures, functionsPortable between Unix/WindowsFree development environmentDecent performance (about 10x less than compiled

C/C++)Many public libraries available for tasks such as

HTML processing and data base accessExtremely large user basethe scripting language of

choice under Unix


49/53

Cons

No GUI building capabilitiesCode may be unreadable after you write it!

Python

Tcl / Tk


50/53

CONCLUSION:

AS WE ARE USING THIS SCRIPTING LANGUAGE IN

REAL TIME VLSI INDUSTRIES, WE HAVE TO BE

EFFICENT IN THIS, OTHER THAN COMPILEING

LANGUAGES


51/53

Perl Documentation

Active Perl installation has best documentation

C:\Perl\html\index.html

General Perl sites http://www.perl.com , http://www.perl.org,

http://www.activeperl.com

Definitive textbook for PerlProgramming Perl3rd edition, L. Wall,

T. Christiansen, R. SchwarzPublished by OReilly, $35 on Amazon.com

Online Perl tutorials http://www.comp.leeds.ac.uk/Perl/start.html

(all of these initial notes are copied from the above tutorial)


52/53


53/53

Documents

Perl, A Hardware Language