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24 Cards in this Set
- Front
- Back
What should you put at the top of a perl program to make it a perl program in unix and also allow it to print warnings.
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#!/usr/bin/perl -w
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What is the general definition of a scalar in Perl. What are some examples of a scalar?
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As a general rule, when perl has just one of something, that is a scalar.
Most scallars are either a number (like 255 or 3.25e20) or a string of characters (like "hello" or the getysburg address) |
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What format are numbers stored as internally in Perl?
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Perl computes ALL numbers with double precision floating-point values. Double precision is defined by the C compiler for the machine that compiled your perl interpretter. Ussually has 15 digits worth of precision and a range e-100 to e+100. This means that there are no integer values as far as perl is concerned.
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How might you clarify the human reading of a really long integer in Perl?
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Perl allows you to place underscore '_' characters in a number, these will no be seen by the perl compiler.
example) 61_298_040_283_768 |
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How do you specify a Nondecimal Integer literal in base 10, binary, and hex respecively?
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0377 #377 octal, same as 255 decimal
0xff #FF hex, also 255 decimal 0b11111111 #also 255 decimal, in binary |
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What is 10.5 % 3.2 in Perl?
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it is 1, because 10.5 and 3.2 are converted to 10 and 3 respectively.
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What is the exponential operator in Perl?
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The exponential operator is **, usage is 2**3 (should equal 8).
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What does perl use to determine when it has reached the end of a string?
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Perl uses length counting, not a null character, to determine the length of a string. Null in no way indicates the length of a string in perl.
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What is a single quoted string literal?
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A single quoted string literal is a sequence of characters enclosed in single quotes. Any character except a backslash and single quote stands for itself inside a string.
Examples: 'fred' 'Don't' 'hello\n' #oddly prints hello\n |
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What is a double quoted string literal?
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A double quoted string literal is a series of characters enclosed in double quotes. However, now the backslash takes on its full power to specify other characters.
"barney" #just the same as 'barney' "hello world/n" #hello world and a newline "coke\tsprite" #coke, a tab, and sprite |
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Is "Barney" the same as 'barney' to Perl?
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yes, it is like the difference between 255 and octal 377, same thing, just looks different.
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String concatenation, how is it done?
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String concatenation is done with the . symbol.
Examples: "Hello"."world" #same as "Helloworld" "hello".' '."world" #same as 'hello world' 'hello world'."\n" #same as "hello world\n" |
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What is the string repetition operator? How does it work?
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The string repetition operator repeats a string a certain number of times.
Example: "fred" x 3 #"fredfredfred" "barney" x (4+1) #barneybarneybarneybarneybarney" 5 x 4 # is really "5" x 4, which is "5555" |
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How are scalar variables in perl referenced?
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Scalar variables in perl are always referenced with the leading $. The shell sometimes you don't use the $VariableName to get the value.
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What is variable interpolation?
Specifically? What happens when you use a variable that has not been filled in? What happens when you mix and match double and single quoted variables? How do you put a variable into a statement and NOT make the variable evaluate as a variable? |
If a variable has not been given a article the variable returns the empty string.
It appears that it always become double quoted. print 'The name is $fred'."\n"; == "The name is \$fred.\n"; # prints a dollar sign |
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What type of mathematical operator precedence does perl follow?
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For mathematical operators, Perl will evaluate them according to normal mathematical rules. For other operators, consult the table on p32.
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What types of Algebraic Operators does Perl use?
What types of String Operators does Perl use? |
Comparison Numeric String
----------------------------------------- Equal == eq Not Equal != ne Less Than < lt Greater Than > gt Less than & Equal <= le Greater Than & Equal >= ge |
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how do you use the if Control Structure in Perl? What is different about the curly braces compared to C++ or Java? What value must be in the evaluation portion of the if?
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if(Evaluation){
#if true }else { #if false } Evaluation must be a scalar. Unlike in C++ and Java, the curly braces are required statements. |
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What are the four existent scalar values that are false?
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undef, 0, '', or '0' are the only false scalar values. All other scalar values are true.
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How do you get user input in perl?
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Use the line input operator <STDIN>. The <STDIN> operator gets the next line of text from your system, if there is nothing waiting to be read, it will wait for the next line of input. A newline is generally appended to the end of the line by <STDIN>
Example: $line = <STDIN>; #puts line of text in $line |
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How function removes the newline character from a string? What does it return? What does it do if there is no newline character?
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use the chomp function. it will return the number of characters removed. If there is no newline, it does nothing and returns nothing.
Example: chomp($text = <STDIN>); #gets next line w/out newline character chomp $text; #for some reason this works as well. |
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What are the specifications for the while control structure?
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while (THIS_VALUE_IS_TRUE){
#Execute this } like if() the block curly braces are required. |
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What is the undef Value?
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The undef Value is most common the value assigned to variables when they have been declared but have not been given a value. It will evaluate to zero or the empty string depending on context.
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What does the defined function do? What is it ussually used for?
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The defined function returns true for all variables that are not set to undef. Because when reading a file, the end of file is marked by returning the undef function, the defined function can be used to determine that no input was available.
Example: defined($madonna) #true if defined, false if $madone contains undef. |