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Explain the @ARGV array in perl
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Date created
Mar 1, 2020
Cards (62)
Section 1
(50 cards)
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", $ARGV[1] will be "arg2"
Explain common hash functions
keys(%hash) values(%hash) each(%hash) delete($hash{keyName}) exists($hash{keyName}) reverse(%hash)
Identify the variable that provides the last index of an array
$#arrayName
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)
Define the open() statement in perl
open(FILEHANDLE, file_mode, "filename.txt") - file mode is either ">", "<" or ">>"; write, read and append respectively
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
Identify the four types of loops in perl
while until for foreach
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);)
Identify the use of comments in perl
- Documenting code - Created by placing a "#" on a line. - Comments are not multi-line
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
unshift(@array, $newValue)
Add a new element to the from of the array with the value $newwValue
List the conditions which evaluate as false
0 undef () -- arrays "" -- string EOF -- end of file "0"
shift(@array)
Removes the first element of the array
Identify how to include modules in perl
use moduleName; Ex: use Roman;
reverse(@array)
reverse the elements of the array
push(@array, $newValue)
Adds a new element to end of the array with value $newValue
Identify the purpose of {} in an "if" statement
Define the execution block of the if statement. Unlike C, the {} braces ARE REQUIRED
Describe the system() function in perl
- used to execute an external command -will output results of command to terminal - returns the exit status of the program that ran - use this for commands that you dont care about SAVING the output to a variable
Explain variable context in perl
- can be scalar, array, or hash context - tells the interpreter what you are looking for (Ex: "$arrayname[$index_number]")
What does $#arrayName return
The value of the last index of the array (NOT the data stored in that array element)
keys(%hash)
returns all of the keys of the hash as an array
Explain assignment of a hash variable for a single hash element
$hashName{keyName}="Value to Add"
What does scalar(@arrayName) return
The size of the array names @arrayName
Explain common array functions
pop(@array) push(@array, $new Value) shift(@array) unshift(@array, $newValue) sort(@array) reverse(@array)
delete($hashName{key})
delete the hash entry with the key given
Explain the use of "if" "if-else" and "if-elsif-else"
flow-control There are also unless conditional flow-control statements
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 $#arrayName = 4 - scalar(@arrayName) returns the size of the array
Describe hash variables in perl
- An associative array
Describe scalar variables in perl
- Singular variable, starts with "$" - Number, characer or string - Perl does automatic type conversion of scalar variables
Explaing assignment of scalar variables in perl
- Assigned using "=" - Ex: $myVariable = 5;
Explain how to write to a filehandle
print(FILEHANDLE "Data to output
");
values(%hash)
returns all of the values of the hash as an array
List the three basic file access modes of the open() function
> write >> append < read
Explain assignment of hash variables in perl (when oringally defining the hash)
%hashname = (key1=>"value1", key2=>"value2", key3=>"Value3")
Interpret the syntax of a while loop
while(condition) { CODE TO EXECUTE }
Identify the two phases of creating a PERL program
1. Editing 2. Execution
sort(@array)
Sort and array alphabetically
Define the two primary methods of executing system commands in perl
- system("command args") - `command args`
Summarize the siz arithmetic comparison operators
< > == <= >= !=
each(%hash)
returns a two element ray of the next key value pair; resultArray[0] is the key resultArray[1] is the value
exists($hashName{keyName})
does the hash key with "keyName" exists
chomp($string)
remove trailing newline
Explain the %ENV hash array
Stores information about the current users environment. You can print this from the command line using printenv
reverse(%hashName)
swap keys for values and values for keys. Will cause issues if there are multiple hash entries with the same value
Define common string manipulation functions
substr($string, $start, $numchars); length($string) lc($string) uc($string) chomp($string) chomp(@string) join(':", @string) split(/\s/, $string) lcfirst($string) ucfirst($string)
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
Describe array variables in perl
- A collection of data (static data, scalar variables, arrays or hashes can all be stored in an array element)
pop(@array)
Removes the last element from the array
Summarize the size string comparison operators
eq ne lt le gt ge
Section 2
(12 cards)