5. History
●
Larry Wall began to develop Perl in 1987
●
The language was originally named Pearl, but there
was a language by that name
●
Perl stands for “Practical Extraction and Report
Language”
●
Rumor has it that the name Perl came first and the
expansion came later
6. Perl Principles
●
There is more than one way to do it
●
Perl: Swiss Army chainsaw of programming
languages
●
No unnecessary limits
●
Perl is the duct tape of the Internet (not as true
as it used to be anymore)
7. What Perl is Used For
●
Internet and Web Scripting
●
Component Integration
●
Database Programming
●
Rapid Prototyping
●
Data Mining
9. Perl's Weaknesses
● Slower than C/C++
● Long and rather steep learning curve
● Code can be difficult to read
Joke: Perl is a “write only” language
Hard even for the original programmer to
read later
11. Resources
● http://www.perl.org - site for everything
that is Perl – documentation, IDEs, tutorials,
links to helpful resourcesa
● http://cpan.perl.org - Comprehensive
Perl Archive Network – a lot of helpful Perl tools
and third-party libraries
13. Perl Distributions
● Linux, Unix, Mac OS – most likely already installed
● http://strawberryperl.com - Perl distribution for various
Windows
“When I am on Windows, I use Strawberry Perl” – Larry Wall
● http://www.activestate.com/activeperl/downloads - Perl
distributions for various platforms
● Q: Which version should I install?
● A: Any version 5.8 or higher should work for this class
14. Online Documentation
● Main website for documentation is
http://perldoc.perl.org/
● ActivePerl installs html version of documentation
● If you install ActivePerl, perldoc command
interactively to get documentation on various Perl
functions
● C:>perldoc -f print
● C:>perldoc -f sqrt
15. Online Documentation
● Perl documentation is divided into sections
● Sections you might find useful as a beginner:
perlrun: How to execute the Perl interpreter
perldata: Perl data types
perlop: Perl operators and precedence
perlfunc: Perl built-in functions
perlre: Perl regular expressions
perlsub: Perl user-defined subroutines
perlsyn: Perl syntax such as loops and conditionals
17. “Hello, Perl!” on Windows
● Create hello_perl.pl in your favorite editor
● Type in the following two lines into that file:
● Run it from command line (set the PATH variable to
point to perl.exe):
C:Perlsrc>perl hello_world.pl
use warnings;
print “Hello, Perl!n”;
18. Notes on Perl's Syntax
●
Whitespace does not matter as in C/C++
●
Curly braces { } group code in blocks as in C/C++
●
Semicolons at the end of statements as in C/C++
●
Unlike in Python, indentation is not required but makes
code legible
19. “Hello, Perl!” on Linux/Unix
●
Call the Perl interpreter directly:
/home/user$ perl hello_perl.pl
●
Run it as a executable script:
Add #!/usr/bin/perl at the beginning of hello_perl.pl
Make the file executable: chmod +x hello_perl.pl
Run it: /home/user$ ./hello_perl.pl
20. -w Warnings Option
●
On Windows, Linux/Unix: >perl -w some_program.pl
●
On Linux/Unix: place #!/usr/bin/perl -w at the
beginning of your program
●
On Windows, Linux/Unix: place use warnings; at the
beginning of your program
21. -w Warnings Option
●
If you run warnings_example.pl, you notice that the
Perl interpreter keeps on chugging even if the value of
the $x variable is not assigned
●
The recommended method is to place use warnings;
at the beginning of your file
●
Place use warnings; at the beginning of every Perl file
you submit as homework
22. Parentheses and Functions
●
Using parentheses with function calls is optional
print "Hellon";
print ("Hellon");
●
If code looks like a function, it is treated as a function
print 1 * 2 + 5; ## prints 7
print (1 * 2 + 5); ## prints 7
23. Adding Two Numbers
●
Source code: add_numbers.pl
●
$num1 - $ is a type identifier that states that the variable
$num1 is a scalar variable, i.e., holds a scalar value
●
The statement $num1 = <STDIN>; reads user input from
<STDIN> and places it into $num1
●
chomp $num1 removes 'n' from the end of the string
●
$sum = $num1 + $num2; converts the values in $num1
and $num2 to numbers, adds them and places the value into
$sum
24. Code Blocks
●
We can use {…} to group statements in a block
●
Blocks can be placed inside other blocks
●
Levels of nesting can be arbitrarily deep
●
Indentation can be used to increase legibility
●
Example: blocks.pl
26. Basic Data Types
●
Perl has four built-in data types: literals, scalars,
arrays, and hashes (dictionaries)
●
A literal is a value that never changes
●
In Perl, there are three types of literals: integers,
floats, and strings
●
A scalar is a single value that can be either a number
or a string
30. Strings
●
In Perl, string processing is called interpolation
●
Single quoted strings are not interpolated with the
exception of and
●
Single quoted strings are treated as ordinary text
●
Double quoted strings are interpolated
●
In double quoted strings, variables are replaced with
their values and escape sequences are processed
32. Strings
use warnings;
## this is useful on Windows
## escaping , aka backwhacking
print "n";
print "C:PerlCS3430n";
print 'C:PerlCS3430 ', "n";
33. q and qq
●
q/some text/ treats some text as a single quoted
string
●
Delimeters after q do not have to be /, they can be {},
[], <>, or ||
print q/C:Perlbinperl.exe/, "n";
print q[/usr/bin/perl.exe], "n";
print q{/usr/bin/perl.exe}, "n";
34. q and qq
●
qq/some text/ treats some text as a double quoted
string
●
Delimeters after qq do not have to be /, they can be {},
[], <>, or ||
print qq{tHe said, "Hello, world!"}, "n";
print qq[t/usr/bin/perl.exe], "n";
print qq|t'"Hi," said Jack. "Have you read a book today?"'n|;
35. Here-Documents
●
A here-document allows you to write large amounts of
text in your program and treat them as strings
●
A here-document starts with << immediately followed by
a start label, then some text, and a terminating label that
must be the same as the start label
●
The terminating label must be on a separate line by
itself with no semicolon
38. Operator Precedence
●
Operators in expressions with parentheses are evaluated
first
●
Exponentiation operators are applied; if there are multiple
such operators, they are applied left to right
●
Multiplication, division operators are applied; if there are
multiple such operators, they are applied left to right
●
Addition and subtraction operators applied; if there are
multiple such operators, they are applied left to right
39. Example
Write a Perl program that evaluates the polynomial y
= a*x^2 + b*x + c at the user-supplied values of a, x,
b, c.
Solution in operator_precedence.pl
40. Assignment Operators
● Perl provides the C-style assignment operators for
abbreviating arithmetic operations in assignment
expressions
● Any statement of the form
variable = variable operator expression;
where operator is one of the binary operators (+, -, *,
/) can be written in the form
variable operator= expression;
42. Increment and Decrement Operators
++$c; increment $c by 1 and use the new value
of $c in the expression where $c
resides
$c++; use the current value of $c in the
expression in which $c resides, then
increment $c by 1
--$c; Same as ++$c except $c is decremented
by 1
$c--; same as $c++ except $c is decremented
by 1
44. String Operators
●
Perl provides a collection of comparison operators on
string scalars
●
String operators are: eq (“equals”), ne (“not equals”), lt
(“less than”), gt (“greater than”), le (“less than or
equal”), ge (“greater than or equal”)
●
Strings are compared alphabetically, with the letters
later in the alphabet having “greater” value
●
“rabbit” gt “dragon” is true, because the ASCII
value of 'r' (114) > the ASCII value of 'd' (100)
46. String Concatenation and Repetition
●
The dot (.) is the string concatenation operator
print “a” . “b” . “c” . “n”;
●
A string s followed by the string repetition operator (x)
followed by an integer n concatenates n copies of s
together
print “Yeah” . “!” x 3 . “n”;
48. Numeric and String Contexts
●
Scalar variables can refer to strings and numbers,
depending on where they occur in the program
●
Perl converts the value to a string or a number
depending on the context in which the scalar variable is
used
●
Uninitialized or undefined variables have the special
value undef which evaluates differently in different
contexts: in a numeric context, undef evaluates to 0; in
a string context, it evaluates to “”
51. if/else & if/elseif/else Selection
Let us implement this pseudocode:
If salesperson's sales >= 100
Print “$1500 bonus!”
Else
If salesperson's sales >= 50
Print “$200 bonus!”
Else
Print “You did not earn your bonus.”
53. do/while and do/until Loops
●
In addition to the standard while and until loops, Perl
has do/while and do/until loops
●
while and until loops check their condition first and then
execute the body of the loop
●
do/while and do/until check their condition after they
execute the body of the loop
54. do/while and do/until Loops
do {
statements;
} while ( condition );
do {
statements;
} until ( condition );
