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Identify the four types of loops in perl
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Cards (62)
Section 1
(50 cards)
Identify the four types of loops in perl
while until for foreach
What does $#arrayName return
The value of the last index of the array (NOT the data stored in that array element)
Identify the use of comments in perl
- Documenting code - Created by placing a "#" on a line. - Comments are not multi-line
Explain assignment of hash variables in perl (when oringally defining the hash)
%hashname = (key1=>"value1", key2=>"value2", key3=>"Value3")
Identify the variable that provides the last index of an array
$#arrayName
List the three basic file access modes of the open() function
> write >> append < read
Identify the two phases of creating a PERL program
1. Editing 2. Execution
Describe scalar variables in perl
- Singular variable, starts with "$" - Number, characer or string - Perl does automatic type conversion of scalar variables
Summarize the size string comparison operators
eq ne lt le gt ge
shift(@array)
Removes the first element of the array
chomp($string)
remove trailing newline
What does scalar(@arrayName) return
The size of the array names @arrayName
Explain the @ARGV array in perl
A special system variable used to pass arguments to script - Ex: perl ./myScript.pl arg1 arg2 --$ARGV[0] will be "arg1", $ARGV[1] will be "arg2"
Describe the command substitution in perl
- uses grave marks `command args`
- returns the output of the command to the variable you specify
- if $output = `command arg` the output is stored all in one variable (all lines seperated by
)
- if @output = `command arg` the output is stored with each line of the output as a different array element
Explain the use of "if" "if-else" and "if-elsif-else"
flow-control There are also unless conditional flow-control statements
Identify the interpreters role in handling syntax errors
- In perl, the interpreter will recognize syntax errors and halt execution BEFORE it begins - Interpreter will output statements; it does not understand and the line which it encountered the error on
Explain the assignment of arrays in perl
@array=("el1", "el2", "el3", 16, 12); - Elements need not be similar data types - Arrays can be assigned or read in scalar context (Ex: $myArray[4] = 2) - Special array $#arrayName give value of last index available in the array. Ex an array of size 5 will have its $#arrayName = 4 - scalar(@arrayName) returns the size of the array
Explain common array functions
pop(@array) push(@array, $new Value) shift(@array) unshift(@array, $newValue) sort(@array) reverse(@array)
Define the two primary methods of executing system commands in perl
- system("command args") - `command args`
sort(@array)
Sort and array alphabetically
Summarize the siz arithmetic comparison operators
< > == <= >= !=
Interpret the syntax of a while loop
while(condition) { CODE TO EXECUTE }
Explain assignment of a hash variable for a single hash element
$hashName{keyName}="Value to Add"
List the conditions which evaluate as false
0 undef () -- arrays "" -- string EOF -- end of file "0"
Define common string manipulation functions
substr($string, $start, $numchars); length($string) lc($string) uc($string) chomp($string) chomp(@string) join(':", @string) split(/\s/, $string) lcfirst($string) ucfirst($string)
values(%hash)
returns all of the values of the hash as an array
Explaing assignment of scalar variables in perl
- Assigned using "=" - Ex: $myVariable = 5;
Describe hash variables in perl
- An associative array
reverse(%hashName)
swap keys for values and values for keys. Will cause issues if there are multiple hash entries with the same value
Explain how to read an entire file into an array (one line per element)
@entireFile=<FILEHANDLE> Again you could chomp this array to get rid of all the newlines (Ex chomp(@entireFile)
keys(%hash)
returns all of the keys of the hash as an array
Define the open() statement in perl
open(FILEHANDLE, file_mode, "filename.txt") - file mode is either ">", "<" or ">>"; write, read and append respectively
unshift(@array, $newValue)
Add a new element to the from of the array with the value $newwValue
reverse(@array)
reverse the elements of the array
Explain common hash functions
keys(%hash) values(%hash) each(%hash) delete($hash{keyName}) exists($hash{keyName}) reverse(%hash)
delete($hashName{key})
delete the hash entry with the key given
Explain variable context in perl
- can be scalar, array, or hash context - tells the interpreter what you are looking for (Ex: "$arrayname[$index_number]")
exists($hashName{keyName})
does the hash key with "keyName" exists
Identify the purpose of {} in an "if" statement
Define the execution block of the if statement. Unlike C, the {} braces ARE REQUIRED
Explain how to write to a filehandle
print(FILEHANDLE "Data to output
");
Describe array variables in perl
- A collection of data (static data, scalar variables, arrays or hashes can all be stored in an array element)
Identify how to include modules in perl
use moduleName; Ex: use Roman;
each(%hash)
returns a two element ray of the next key value pair; resultArray[0] is the key resultArray[1] is the value
push(@array, $newValue)
Adds a new element to end of the array with value $newValue
pop(@array)
Removes the last element from the array
Describe the system() function in perl
- used to execute an external command -will output results of command to terminal - returns the exit status of the program that ran - use this for commands that you dont care about SAVING the output to a variable
Identify what modules are in perl
- Synonymous with header files in C - Collection of like functions and variables that may be used in your program
Explain the %ENV hash array
Stores information about the current users environment. You can print this from the command line using printenv
Interpret the syntax of the foreach loop
foreach $element(@arrayName) { CODE TO EXECUTE } In this case $element is a reference to a specific element of @arrayName. If you change the value of $element, the value will change in the array as well
Explain how to read a line from a file handle
$line=<FILEHANDLE> To get rid of the newline in $line, you could now chomp() (Ex: chomp($line);)
Section 2
(12 cards)