Perl Script Writing

Front 1

how can you check the version of perl?

Back 1

perl -v

Front 2

What is a package for?

Back 2

Packages allow you to define a distinct namespace for a given block of code. A namespace is a table of variable names.

Front 3

Why use namespaces?

Back 3

organize code ensure reusability prevent errors if an identifier is overwritten

Front 4

What does the package keyword do?

Back 4

Package keyword assigns the current package

Front 5

Where can you use the package keyword at in a perl script?

Back 5

Anywhere

Front 6

How are packages organized inside a file

Back 6

1 file=1 package or ??

Front 7

How would you write a package statement

Back 7

#!/bin/perl -w .... not part of package package Elephant; $myString = "The elephant" ... all other lines are part of package Elephant package Fox; $myString = "The fox" $myString variable has two different values depending on what package is used Fox or Elephant

Front 8

Where are all Perl symbols such as variables

Back 8

file handles

Front 9

How do you access the $myString variable item in a symbol table for the Elephant package? How about for the default package?

Back 9

%Elephant::myString - Elephant package and $myString package Elephant; $myString = "The slow elephant"; package main; print $Elephant::myString;

Front 10

How do you nest a Fox package after an Animal package

Back 10

package Animal; ..... package Animal::Fox; #use colons to make a nested package $myString = "The fox"; package Animal::Elephant; #now nested inside another package package main; print $Animal::Elephant::myString

Front 11

What is the purpose of BEGIN and END block statements?

Back 11

The BEGIN is executed first before rest of script and END? #!C:perl\bin\perl.exe END { print("Gamma\n");} #executed last print ("we are playing\n"); #this is where it goes... BEGIN { print("start here\n");} #executed first

Front 12

What are modules? What are they for?

Back 12

Distinct Perl scripts with a .pm ending. foo.pm or help.pm They must have a package other than main.... Perl modules help reuse software

Front 13

How do you use a module in another Perl script?

Back 13

The use and require statement.

Front 14

What do modules have in them?

Back 14

Subroutines and variables?

Front 15

What does the require statement do? require Foo;

Back 15

The require:Foo means that you want to include the Foo module and all the functionality in there.

Front 16

How does file search for Perl Modules from the required modules?

Back 16

The require keyword triggers Perl to search for the Perl module in the local directory and the @INC array path (include path).

Front 17

How do you use the SolveSub subroutine in the Perl module Foo and include the module in your program.

Back 17

require Foo; print Foo::SubSolve("10 0.5 * -2");

Front 18

What is the use statement for? use Foo("solve"); or use Foo ("solve"

Back 18

"\?token");

Front 19

Can you use the "use" statement to select only specific subroutines to export? use Foo ("solve"

Back 19

"\$token); will this be allowed?

Front 20

What is the difference between the require statement and the use statement?

Back 20

use statements look for modules during compilation then loads the module and runs code before compiling the rest of the file?

Front 21

What is in a Perl Module (.pm file)?

Back 21

Perl modules have a package and several supporting subroutines

Front 22

What does the perl -w switch enable?

Back 22

#NAME?

Front 23

How do you activate the -w switch?

Back 23

#!\usr\bin\perl -w (put the -w in the first line)

Front 24

How can you use the print command to help with debugging?

Back 24

Use print at specific checkpoints: print("Checkpoint 2\n"); ...... print("Checkpoint 3\n");

Front 25

what does the strict module do to help debug perl programs?

Back 25

Requires that all variables be declared before they are used.

Front 26

How does the strict module require you to declare references

Back 26

variables

Front 27

How can you use the strict module to restrict only subroutines need to be declared before use but allow undeclared variables?

Back 27

use strict 'subs'; no strict 'variables';

Front 28

What is the my() funtion for?

Back 28

Allows you to declare your variables ahead of time.

Front 29

How can you run the Perl Debugger

Back 29

use perl -d prog.pl

Front 30

What can you do with the debugger?

Back 30

Examine source code set breakpoints display function stack check variables change variables

Front 31

Can you use the debugger to detect compile time errors?

Back 31

Perl debuggers can only check during run time

Front 32

While in the debugger how can you single step through the card?

Back 32

Press the s-key

Front 33

What are some of the Perl debugger commands?

Back 33

L - lists all breakpoints b sets a breakpoint at current execution line d =deletes a break break D deletes all breakpoints c-continue p-prints out breakpoint V main (list variables)

Front 34

The assignment operator is: ?

Back 34

=

Front 35

A scalar variable is what? what does it start with?

Back 35

a single value like string or number It always starts with $

Front 36

what are the binary operators for add

Back 36

subtract

Front 37

What are the perl unary operators

Back 37

#NAME?

Front 38

Why do we have operators in perl and what are the three types?

Back 38

(i.e. binary

Front 39

What is a string variable?

Back 39

A scalar variable that stores a string?

Front 40

How do you set the scalar variable $joe to the stirng value: Joe Baby

Back 40

$joe="Joe Baby";

Front 41

What is <STDIN>?

Back 41

A special data type known as a list

Front 42

What happens when the perl interpreter sees the <STDIN> on a line?

Back 42

It waits for the user to respond with a character sequence of data and presses the Enter key.

Front 43

When a user inputs a line of text into <STDIN> what gets brought with it in addition to the character?

Back 43

The perl interpreter automatically retrieves the newline character as well \n.

Front 44

How can you get rid of the new line character at the end of a string? $age = <STDIN>; actually received "30\n" not "30" so need to get rid of the \n in this case.

Back 44

chomp($age)

Front 45

What is a Perl Package end with?

Back 45

Ends with a 1: to show the module completed successfully.

Front 46

What is the our keyword for?

Back 46

The our keyword declares a variable to be global to the module.

Front 48

Is <STDIN> a file handle or a special variable?

Back 48

A filehandle

Front 49

How do you display Executing your script to the user when your program starts?

Back 49

print ("Executing your script\n");

Front 50

What is the numeric boolean operator for not equal to?

Back 50

!=

Front 51

What is the numeric boolean operator for equal to?

Back 51

==

Front 52

what is returned from this boolean expression $a = 100; $b = 150; print $a == $b;

Back 52

Nothing is returned

Front 53

what is returned from this boolean expression $a = 100; $b = 100; print $a == $b;

Back 53

Since the value is TRUE

Front 54

What are the different types of boolean operators?

Back 54

< <= > >= == !=