$ cat first.perl #displays contents of script

#!/usr/bin/perl #

Scalar

• variable that holds single value string or number

$first_name="Jeanie";

$var="net";
print "${var}work"; #prints network

$now = localtime(); # prints local time Perl Function

Functions

defined Function - check for validity of a variable 1-defined; null if not defined

$name = "Tommy";
print "Okay \n" if defined $name;

undef Function - undefines a defined variable releases storage for arrays and subroutines

undef $name;

$_ - scalar variable - Holds the current line - $_ is the default output for the print function

$_="Jeanie";
print; #prints Jeanie

Array

• an ordered list of scalars, indexed starting at 0

@names=("Jackson", "Penny", "Lily")

print "@names"; #prints the array

print "$names[0]"; #prints Jackson

print "$names[-1]"; #prints Lily

$names[3]="Smokie"; #assigns a new value as the 4th element

$size=@names; # the size of the array

$#arrayname - returns the last subscript (index) in the array.

@digits=(0..10); #numbers 0 - 10

@letters= ('A'..'Z, 'a'.. 'z''); # list of upper and lower case letters

@n=(-5..20); #numbers -5 - 20

The resulting array when elements of one array are assigned the values from another array

@names=qw/jackson, lily, penny, jeanie, alex, lew/;
@pal=@names[2,3];
print "@pal";

• called tables or matrices
• consist of rows and columns
• two dimensional array - first subscript represents the row and the second subscript represents the column
• Each row enclosed in [ ] - unnamed list
• there is an implied -> between adjacent brackets
• -> arrow operator infix operator - can be used to get an individual element of an array. If the right side is either a [...] , {...} , or a (...) subscript, then the left side must be either a hard or symbolic reference to an array, a hash, or a subroutine respectively

# A two-dimensional array consisting of 4 rows and 3 columns
@matrix=( [ 3 , 4, 10 ], # Each row is an unnamed list
[ 2, 7, 12 ],
[ 0, 3, 4 ],
[ 6, 5, 9 ],
) ;
print "@matrix\n"; #prints the addresses of the four anonymous arrays
print "Row 0, column 0 is $matrix[0][0].\n"; #can also be written: $matrix[0]->[0]

print "Row 1, column 0 is $matrix[1][0].\n"; # can also be written: $matrix[1]->[0]
for($i=0; $i < 4; $i++){
for($x=0; $x < 3; $x++){
print "$matrix[$i][$x] ";
}
print "\n";
}

• pop removes last element
• push adds new elements to the end of the array
• shift removes first element
• unshift adds new elements to the beginning of the array
• sort sorts the elements of an array

Hash

• an associative array
• an unordered list of key/value pairs, indexed by strings
• Key - the first string in the pair of strings - left side
• Value - the second string - right side
• Hash must be defined first
• => digraph operator

%employee=(
"Name" => "Jeanie",
"City"=>"Winston Salem",
"State"=>"NC"
);
print "$employee{"Name"}"; #prints Jeanie$employee{"zip"}="27012"; #assigns a key / value

%seasons=("Sp" => "Spring",
"Su" => "Summer",
"F" => "Fall",
"W" => "Winter",
);
%days=("Mon" => "Monday",
"Tue" => "Tuesday",
"Wed" => undef,
);
$days{"Wed"}="Wednesday";
$days{5}="Friday";

keys Function

• returns in random order the keys of the array

keys(ASSOC_ARRAY)

# The keys function returns the keys of a hash
%weekday= (
'1'=>'Monday',
'2'=>'Tuesday',
'3'=>'Wednesday',
'4'=>'Thursday',
'5'=>'Friday',
'6'=>'Saturday',
'7'=>'Sunday',
);
foreach $key ( keys(%weekday) ){print "$key ";}
print "\n";
foreach $key ( sort keys(%weekday) ) {
print "\t$key\t $weekday{$key}\n";
}
print "\n";

values Function

• returns in random order an array of the values of a hash

# The values function returns the values in a hash
%weekday= (
'1'=>'Monday',
'2'=>'Tuesday',
'3'=>'Wednesday',
'4'=>'Thursday',
'5'=>'Friday',
'6'=>'Saturday',
'7'=>'Sunday',
);
foreach $value ( values(%weekday)){print "$value\n";}
print "\n";

foreach $value ( sort values(%weekday) ){print "$value\n ";}
print "\n";

Sort Hash by Values in Ascending Order

# Sorting a Hash by Value in Descending Order
sub asc_sort_wins {
$wins{$a} <=> $wins{$b};
}

# Sorting a Hash by Value in Descending Order
sub desc_sort_wins {
$wins{$b} <=> $wins{$a}; # Reverse $a and $b
}

%wins = (
"Portland Panthers" => 123410,
"Sunnyvale Sluggers" => 12,
"Chico Wildcats" => 5,
"Stevensville Tigers" => 6,
"Lewiston Blazers" => 11,
"Danville Terriors" => 8,
);

print "\nWins in Ascending Numeric Order by value:\n\n";
foreach $key (sort asc_sort_wins(keys(%wins))) {
printf "\t% -30s%5d\n", $key, $wins{$key};
}

print "\nWins in Descending Numeric Order by value:\n\n";
foreach $key (sort desc_sort_wins(keys(%wins))) {
printf "% -20s%5d\n", $key, $wins{$key};
}
print "\nSort Teams in Ascending Order by key:\n\n";
foreach $key( sort(keys(%wins))) {
printf "\t% -20s%5d\n", $key, $wins{$key};
}
print "\nSort Teams in Reverse Order by key:\n\n";
foreach $key( reverse sort(keys (%wins))) {
printf "\t% -20s%5d\n", $key, $wins{$key};
}

delete Function

• deletes a value from a hash
• deleted value return if successful

delete $ASSOC_ARRAY{KEY}

#!/usr/bin/perl
%employees=(
"Nightwatchman" => "Joe Blow",
"Janitor" => "Teddy Plunger",
"Clerk" => "Sally Olivetti",
);

$layoff=delete $employees{"Janitor"};
print "We had to let $layoff go.\n";
print "Our remaining staff includes: ";
print "\n";
while(($key, $value)=each(%employees)){
print "$key: $value\n";
}

exists Function

• true if a hash key has been defined
• false if not

exists $ASSOC_ARRAY(KEY)

%employees=( "Nightwatchman" => "Joe Blow",
"Janitor" => "Teddy Plunger",
"Clerk" => "Sally Olivetti",
);

print "The Nightwatchman exists.\n" if exists
$employees{"Nightwatchman"};
print "The Clerk exists.\n" if exists $employees{"Clerk"};
print "The Boss does not exist.\n" if not exists $employees{"Boss"};

Hash Built in Functions

• keys retrieves all the keys in a hash
• values retrieves all the values in a hash
• each retrieves a key/value pair from a hash
• delete removes a key/value pair

Constant

• once set, cannot be modified.

use constant BUFFER_SIZE => 4096;

use constant DEBUGGING => 0;

use constant ISBN => "0-13-028251-0";

ISBN="9-12-765438-0"; # Cannot modify ISBN; produces an error.

Numbers

• decimal, octal, hexadecimal), floating point numbers, scientific notation, Booleans, and null.

$year = 2006; # integer

$mode = 0775; # octal number in base 8

$product_price = 29.95; # floating point number in base 10

$favorite_color = 0x33CC99; # integer in base 16 (hexadecimal)

$distance_to_moon=3.844e+5; # floating point in scientific notation

$bits = 0b10110110; # binary number

Single and Double Quotes

• single Quotes - all characters are treated as literals
• Double Quotes - Variables and special escape sequence ($ @ \) are understood.
• make sure the quotes are matched
• backslash sequences (\n, \t, \", etc.) are interpreted within double quotes
• a backslash will escape a quotation mark, a single quote can be embedded in a set of double quotes, and a double quote can be embedded in a set of single quotes.

$question = 'He asked her if she wouldn\'t mind going to Spain'; # Single quotes

$answer = 'She said: "No, but it rains in Spain."'; # Single quotes

$line = "\tHe said he wouldn't take her to Spain\n";

$temperature = "78";

print "It is currently $temperature degrees";

# Prints: "It is currently 78 degrees.". Variables are

# interpreted when enclosed in double quotes, but not # single quotes

Here Document

• is a block of text embedded between user-defined tags, the first tag preceded by <<.
• NOTE: make sure there is not space after print

print<<END;
  It
  rains in
   Spain
END

Alternative Quotes

• qq - double quote
• q - single quote
• qw - a quoted list of words ("January", "February", "March ")
• qx - back quotes

print qq/Hello\n/; # same as: print "Hello\n";

print q/He owes $5.00/, \n"; # same as: print 'He owes $5.00', "\n";

@states=qw( ME MT CA FL ); # same as ("ME", "MT", "CA","FL")

$today = qx(date); # same as $today = 'date';

• q/Hello/
• q#Hello#
• q(Hello)
• q{Hello}
• q[Hello]

Delimiter can be a non alphanumeric character such as #, !, or paired characters as ( ) , [ ], { }

• q#Hello#
• q(Hello)

printf();

• Note: make sure there is not space after printf(
• print function prints a formatted string to the selected filehandle, default being STDOUT
• Return value
• 1 - successful
• 0 - fails
• quoted string followed by comma and list of comma separated arguments

printf("<p>The name is %s and the number is %d</p>\n", "John", 50);

sprintf

• just like printf function except it alls you to assign the formatted string to a variable

$coin_toss = int (rand(2 )) + 1; # Generate a random # number between 1 and 2

if( $coin_toss == 1 ) {

print "You tossed HEAD\n";

}

else {

print "You tossed TAIL\n";

}

# 1 is Monday, 7 Sunday

$day_of_week = int(rand(7)) + 1;

print "Today is: $day_of_week\n";

if ( $day_of_week >=1 && $day_of_week <=4 ) {

print "Business hours are from 9 am to 9 pm\n";

} elsif ( $day_of_week == 5) {

print "Business hours are from 9 am to 6 pm\n";

} else {

print "We are closed on weekends\n";

}

$coin_toss = int (rand(2 )) + 1; # Generate a random number

# between 1 and 2

print ( $coin_toss == 1 ? "You tossed HEAD\n" : "You tossed TAIL\n" );

while/until Loop

• As long as the expression tests true, the loop continues to iterate

$count=0; # Initial value
while ($count < 10 ){

# Test print $n;

$count++; # Increment value

}

do-while

$count=0; # Initial value

do {

print "$n ";

$count++; # Increment value

while ($count < 10 ); # Test

}

• first expression inititializes a variable and is evaluated only once.
• second tests whether the value is true, and if it is true, the block is entered;
• if not, the loop exits.

for( $count = 0; $count < 10; $count = $count + 1 ) {

print "$count\n";

}

@dessert = ( "ice cream", "cake", "pudding", "fruit");

foreach $choice (@dessert){

# Iterates through each element of the array

echo "Dessert choice is: $choice\n";

}

$n=0;

while( $n < 10 ){

print $n;

if ($n == 3){

last; # Break out of loop

} $n++;

}

print "Out of the loop.<br>";

Subroutines/Functions

• block of code that performs a task and can be invoked from another part of the program. Data can be passed to the function via arguments. A function may or may not return a value.
• Variables outside the function are available inside the function. The my function will make the specified variables local.

$my_year = 2000;
if ( is_leap_year( $my_year ) ) { # Call function with an argument
print "$my_year is a leap year\n";
}
else {
print "$my_year is not a leap year";
}

sub is_leap_year { # Function definition
my $year = shift(@_); # Shift off the year from
# the parameter list, @_
return ((($year % 4 == 0) && ($year % 100 != 0)) || ($year % 400 == 0)) ? 1 : 0; # What is returned from the function
}

Files

• the open function to open files, and pipes for reading, writing, and appending. The open function takes a user-defined filehandle (normally a few uppercase characters) as its first argument and a string containing the symbol for read/write/append followed by the real path to the system file.

To open a file for reading:

open(FH, "<filename"); # Opens "filename" for reading.

# The < symbol is optional.

open (DB, "/home/ellie/myfile") or die "Can't open file: $!\n";

To open a file for writing:

open(FH, ">filename"); # Opens "filename" for writing.

# Creates or truncates file.

To open a file for appending:

open(FH, ">>filename"); # Opens "filename" for appending.

# Creates or appends to file.

To open a file for reading and writing:

open(FH, "+<filename"); # Opens "filename" for read, then write.

open(FH, "+>filename"); # Opens "filename" for write, then read.

To close a file:

close(FH);

To read from a file:

while(<FH>){ print; } # Read one line at a time from file.

@lines = <FH>; # Slurp all lines into an array.

print "@lines\n";

To write to a file:

open(FH, ">file") or die "Can't open file: $!\n";

print FH "This line is written to the file just opened.\n";

print FH "And this line is also written to the file just opened.\n";

To Test File Attributes

print "File is readable, writeable, and executable\n" if -r $file and -w _ and -x _;

# Is it readable, writeable, and executable?

print "File was last modified ",-M $file, " days ago.\n";

# When was it last modified?

print "File is a directory.\n " if -d $file; # Is it a directory?

Filehandles

• STDIN -
• STDOUT - output to the terminal screen
• STDERR - printing errors
• names given to predefined streams
• stdin
• stdout
• stderr
• <STDIN> next line of standard input can be read from the terminal
• retains new line at the end of string Must chomp or chop
• DATA - gets data from the same script

Ctrl-d UNIX

Ctrl-z Windows

95

100

• Perl 5
• remove the last character in a scalar variable and the last character of each word in an array ONLY if that character is the new line

• reads a number of bytes into a variable from a specified filehandle.
• Standard input is STDIN
• Returns the number of bytes read.

number_of_bytes=read(FILEHANDLE, buffer, how_many_bytes);

• gets a single character from the keyboard or from a file
• at EOF, returns a null string

# Getting only one character of input
print "Answer y or n ";
$answer=getc; # Gets one character from stdin
$restofit=<>; # What remains in the input buffer is
# assigned to $restofit
print "$answer\n";
chomp($restofit);
if ($restofit ne "")
{print "The characters left in the input buffer were:*$restofit*\n" if defined $restofit;}

# Assign input to a hash
$course_number=101;
print "What is the name of course $course_number?";
chomp($course{$course_number} = <STDIN>);
print %course, "\n";

returns true if array index or hash key has been defined and false if not.

#!/usr/bin/perl
@names = qw(Tom Raul Steve Jon);
print "Hello $names[1]\n", if exists $names[1];
print "Out of range!\n", if not exists $names[5];

remove a value from a n element of an array but not the element itself. The deleted value is undefined.

@colors=("red","green","blue","yellow");
print "@colors\n";
delete $colors[1];
print "@colors\n";
print $colors[1],"\n";

evaluates the expression (EXPR) for each element of the array *(LIST)

# Searching for patterns in a list
@list = (tomatoes, tomorrow, potatoes, phantom, Tommy);
$count = grep( /tom/i, @list); #counts the items 4 items found
@items= grep( /tom/i, @list); #assigns the items to a new array
print "Found items: @items\nNumber found: $count\n";

joins the elements of an array into a single sting and separates each with the given delimiter (the opposite of split)

join (DELIMITER, LIST)

# Joining each elements of a list with colons
$name="Joe Blow";
$birth="11/12/86";
$address="10 Main St.";
print join(":", $name, $birth, $address ), "\n";

pops off the last element of an array and return it. The array size is decrease by 1.

$got=pop(@names);

pushes values onto the end of an array

push(ARRAY, LIST)

push(@names, "Jim", "Joseph", "Archie");

shifts off and returns the first element of an array decreasing size by one

If ARRAY is omitted the ARGV array is shifted and if in a subroutine, the @_arry is shifted

removes and replaces elements in an array.

splice (ARRAY, OFFSET, LENGTH, LIST)

OFFSET - the starting position
LENGTH - the number of items to be removed
LIST - new elements to replace the old ones

@discarded = splice(@colors, 2, 2);

split Function

• splits up a string by some delimiter (white space by default) and returns an array.
• DELIMITER -
• EXPR - string to be split - defaults to $_
• LIMIT - number of fields that can be split. Any remaining fields are part of the last one.

split("DELIMITER",EXPR, LIMIT)

$line="a b c d e";
@letter=split(' ',$line);

114

122

sort Function

• sorts and returns a sorted array
• if subroutine is omitted, sorts in string comparison order (alphabetically)
• if subroutine is specid9ied the argument to sort is the name of the subroutine followed by a list of the values to be sorted.
• cmp operator - values in the list will be sorted alphabetically (ASCII sort)
• <=> operator (called the space ship) operator - the values sorted numerically and passed to the subroutine and received by special Perl variables $a and $b

sort (SUBROUTINE, LIST)

@list=("dog","cat", "bird","snake" );
print "Original list: @list\n";
# Ascii sort using a subroutine
sub asc_sort{
     $a cmp $b; # Sort ascending order
}

@sorted_list=sort asc_sort(@list);
print "Ascii sort: @sorted_list\n";

# Numeric sort using subroutine
sub numeric_sort {
     $a <=> $b ;
} # $a and $b are compared numerically

@number_sort=sort numeric_sort 10, 0, 5, 9.5, 10, 1000;
print "Numeric sort: @number_sort.\n";

# Sorting numbers with an unamed subroutine
@sorted_numbers= sort {$a <=> $b} (3,4,1,2);
print "The sorted numbers are: @sorted_numbers", ".\n";

reverse Function

• reverses the elements in an array

@sorted = reverse (sort(@list));

unshift Function

• prepends LIST to the front of the array.

unshift (ARRAY, LIST)

# Putting new elements at the front of a list
@names=("Jody", "Bert", "Tom") ;
unshift(@names, "Liz", "Daniel");
print "@names\n"; #Liz Daniel Jody Bert Tom

Pipes

• Pipes can be used to send the output from system commands as input to Perl and to send Perl's output as input to a system command. To create a pipe, also called a filter, the open system call is used. It takes two arguments: a user-defined handle and the operating system command, either preceded or appended with the "|" symbol. If the command is preceded with a "|", the operating system command reads Perl output. If the command is appended with the "|" symbol, Perl reads from the pipe; if the command is prepended with "|", Perl writes to the pipe.

Input filter

open(F, " ls |") or die; # Open a pipe to read from

while(<F>){ print ; } # Prints list of UNIX files

Output filer

open(SORT, "| sort" ) or die; # Open pipe to write to

print SORT "dogs\ncats\nbirds\n"

# Sorts birds, cats, dogs on separate lines.

Regular Expressions - Pattern Matching

• set of characters or pattern enclosed in forward slashes to match patterns in text and to refine searches and substitutions

print if

print if /Norma/; #prints line if Norma found

print $_ if $_ =~ /Norma/; # same as above line

print if else

print $x unless $x==6;

print unless /Norma/; #prints all lines with out Norma

print while

print $x++,"\n" while $x!= 5; #prints 1 - 4

print until

print $x++,"\n" until $x== 5; #prints 1 - 4

print foreach

@alpha=(a .. z, "\n");
print foreach @alpha;

Matching Patterns

m Modifier - matching patterns (m optional if using //)

/Regular Expression/ # same as m/Regular Expression/
m#Regular Expression#
m{Regular Expression} # can use { } ( ) [ ] <>

g Modifier - Global match

m /search pattern/g

$_ = "I lost my gloves in the clover, Love.";
@list=/love/g;
print "@list.\n"; #prints love love. Does not print Love because uppercase

i Modifier - run off case sensitivity

$_ = "I lost my gloves in the clover, Love.";
@list=/love/gi;
print "@list.\n"; #prints love love Love.

Special Scalars

$& - saves the search word

$_="San Francisco to Hong Kong\n";
/Francisco/; # Save 'Francisco' in $& if it is found
print $&,"\n";
/to/;
print $Ô,"\n"; # Save what comes before the string 'to'

/to\s/; # \s represents a space
print $Õ, "\n"; # Save what comes after the string 'to'

x Modifier - place comments within the regular expression and add whiter space characters (spaces, tabs, new lines) for clarity

$_="San Francisco to Hong Kong\n";
/Francisco # Searching for Francisco
/x;
print "Comments and spaces were removed and \$& is $&\n";

Objects

Perl Class

a package containing a collection of variables and function called properties (attributes) and methods.

%ENV Hash

contains environment variables handed to Perl

%SIG Hash

set signal handlers for signals

%INC Hash

• contains the entries for each filename that has been included via the do or require function
• key - filename
• value is the location

perldoc -f reverse

• type at command prompt

Regular expression meta characters are characte4rs that do not represent themselves.

• meta characters lose their special meaning if preceded with a backslash (\)

/^a . . . c/

• caret(^) matches for a string only if it is at the beginning of the line.
• period(.) used to match any single character including white space except a newline
• [a-z0-9_] matches any single character in set

while(<DATA>){
print if /[A-Z][a-z]eve/; //prints if one capital letter, one lowercase letter and eve
}
__DATA__
Steve Blenheim 101
Betty Boop 201
Igor Chevsky 301
Norma Cord 401
Jonathan DeLoach 501
Karen Evich 601

while(<DATA>){ \\special DATA filehandle gets its input fro the text after the __DATA__ token. The while loop is entered and the first line following the __DATA__ token is read in and assigned to $_.
print "Found Norma!\n" if /N..ma/;
}
__DATA__
Steve Blenheim 101
Betty Boop 201
Igor Chevsky 301
Norma Cord 401
Jonathan DeLoach 501
Karen Evich 601

• [^a-z0-9_] matches any single character not in set

while(<DATA>){
print if / [^123]0/; //prints if matches pattern one space, one number not in the range between 1 and 3, followed by 0
}

• \d matches one digit represents the character class [0-9]
• \D matches a nondigit, same as [^0-9]
• \w matches an alphanumeric (word) character; same as [a-z0-9_]
• \W matches a non alphanumeric (non word) character; same as [^a-z0-9_]
• .\s matches a white space character, such as space, tabs, and newline's

# The s modifier and the newline
$_="Sing a song of sixpence\nA pocket full of rye.\n"; //scalar is assigned
print $& if /pence./s; //$& holds the pattern found in the last successful search id pence\n
print $& if /rye\../s; //\. means literal period (.) Searches for rye.\n
print if s/sixpence.A/twopence, a/s; \\smodifier allows the dot to match on the new line character

• \S matches nonwhite space characters
• \n matches a new line
• \r matches a return
• \t matches a tab
• \f matches a form feed
• \b matches a backspace
• \0 matches a null character
• \b matches a word boundary (when not inside [ ])
• \B matches a non word boundary
• ^ matches to beginning of line
• $matches to end of line
• \A matches to the beginning of the string only
• \Z matches to the end of the string or line
• \z matches to the end of the string only
• \G matches when previous m//g left off

Greedy Metacharacters

• x? matches 0 or 1 x
• x* matches 0 or more occurrences of x
• x+ matches 1 or more occurrences of x

• (xyz)+ matches 1 or more patterns of xyz
• x{m,n} matches at least m occurrences of x and no more than n occurrences of x
• was|were\will matches one of was, were, or will
• (string) used for back referencing
• \1 or $1 matches first set of parentheses
• \2 or $2 matches second set of parentheses

POSIX Character Class

• Portable Operating System Interface used to ensure that programs are portable across operating systems.
• different countries may vary the in way characters are encoded, the symbols used for currency, how times ns dates are represented.

Bracket Class Meaning

[:alnum:] alphanumeric characgters

[:alpha:] alphabetic characters

while(<DATA>){
print if /[[:upper:]][[:alpha:]]+ [[:upper:]][[:lower:]]+/; #Pattern=upper letter+one or more alphebetic lower case letters+ space + upper letter +one or more alphebetic lower case letters
}