perl course-in-mumbai

WELCOME TO
Vibrant Technology & Computers
Vashi,Navi Mumbai
www.vibranttechnologies.c
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www.vibranttechnologies.co.in 2

What is Perl?
 Practical Extraction and Report Language
 Interpreted Language
◦ Optimized for String Manipulation and File I/O
◦ Full support for Regular Expressions
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Running Perl Scripts
 Windows
◦ Download ActivePerl from ActiveState
◦ Just run the script from a 'Command Prompt'
window
 UNIX – Cygwin
◦ Put the following in the first line of your script
#!/usr/bin/perl
◦ Run the script
% perl script_name
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Basic Syntax
 Statements end with semicolon ‘;’
 Comments start with ‘#’
◦ Only single line comments
 Variables
◦ You don’t have to declare a variable before you
access it
◦ You don't have to declare a variable's type
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Scalars and Identifiers
 Identifiers
◦ A variable name
◦ Case sensitive
 Scalar
◦ A single value (string or numerical)
◦ Accessed by prefixing an identifier with '$'
◦ Assignment with '='
$scalar = expression
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Strings
 Quoting Strings
◦ With ' (apostrophe)
 Everything is interpreted literally
◦ With " (double quotes)
 Variables get expanded
◦ With ` (backtick)
 The text is executed as a separate process, and the
output of the command is returned as the value of
the string
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String Operation Arithmetic
lt less than <
gt greater than >
eq equal to ==
le less than or equal to <=
ge greater than or equal to >=
ne not equal to !=
cmp compare, return 1, 0, -1 <=>
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Comparison Operators

Operator Operation
||, or logical or
&&, and logical and
!, not logical not
xor logical xor
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Logical Operators

Operator Operation
. string concatenation
x string repetition
.= concatenation and assignment
$string1 = "potato";
$string2 = "head";
$newstring = $string1 . $string2; #"potatohead"
$newerstring = $string1 x 2; #"potatopotato"
$string1 .= $string2; #"potatohead"
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String Operators
Check concat_input.pl

Perl Functions
 Perl functions are identified by their unique names
(print, chop, close, etc)
 Function arguments are supplied as a comma
separated list in parenthesis.
◦ The commas are necessary
◦ The parentheses are often not
◦ Be careful! You can write some nasty and unreadable
code this way!
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Check 02_unreadable.pl

Lists
 Ordered collection of scalars
◦ Zero indexed (first item in position '0')
◦ Elements addressed by their positions
 List Operators
◦ (): list constructor
◦ , : element separator
◦ []: take slices (single or multiple element chunks)
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List Operations
 sort(LIST)
a new list, the sorted version of LIST
 reverse(LIST)
a new list, the reverse of LIST
 join(EXPR, LIST)
a string version of LIST, delimited by EXPR
 split(PATTERN, EXPR)
create a list from each of the portions of EXPR that match
PATTERN
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Check 03_listOps.pl

Arrays
 A named list
◦ Dynamically allocated, can be saved
◦ Zero-indexed
◦ Shares list operations, and adds to them
 Array Operators
◦ @: reference to the array (or a portion of it, with [])
◦ $: reference to an element (used with [])
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Array Operations
 push(@ARRAY, LIST)
add the LIST to the end of the @ARRAY
 pop(@ARRAY)
remove and return the last element of @ARRAY
 unshift(@ARRAY, LIST)
add the LIST to the front of @ARRAY
 shift(@ARRAY)
remove and return the first element of @ARRAY
 scalar(@ARRAY)
return the number of elements in the @ARRAY
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Check 04_arrayOps.pl

Associative Arrays - Hashes
 Arrays indexed on arbitrary string values
◦ Key-Value pairs
◦ Use the "Key" to find the element that has the "Value"
 Hash Operators
◦ % : refers to the hash
◦ {}: denotes the key
◦ $ : the value of the element indexed by the key (used
with {})
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Hash Operations
 keys(%ARRAY)
return a list of all the keys in the %ARRAY
 values(%ARRAY)
return a list of all the values in the %ARRAY
 each(%ARRAY)
iterates through the key-value pairs of the %ARRAY
 delete($ARRAY{KEY})
removes the key-value pair associated with {KEY} from the
ARRAY
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Arrays Example
#!/usr/bin/perl
# Simple List operations
# Address an element in the list
@stringInstruments =
("violin","viola","cello","bass");
@brass =
("trumpet","horn","trombone","euphonium","t
uba");
$biggestInstrument = $stringInstruments[3];
print("The biggest instrument: ",
$biggestInstrument);
# Join elements at positions 0, 1, 2 and 4 into a
white-space delimited string
print("orchestral brass: ",
join(" ",@brass[0,1,2,4]),
"n");
@unsorted_num = ('3','5','2','1','4');
@sorted_num = sort( @unsorted_num );
# Sort the list
print("Numbers (Sorted, 1-5): ",
@sorted_num,
"n");
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#Add a few more numbers
@numbers_10 = @sorted_num;
push(@numbers_10, ('6','7','8','9','10'));
print("Numbers (1-10): ",
@numbers_10,
"n");
# Remove the last
pop(@numbers_10),
"n");
# Remove the first
shift(@numbers_10),
"n");
# Combine two ops
print("Count elements (2-9): ",
$#@numbers_10;
# scalar( @numbers_10 ),
"n");
print("What's left (numbers 2-9): ",
@numbers_10,
"n");

Hashes Example
#!/usr/bin/perl
# Simple List operations
$player{"clarinet"} = "Susan Bartlett";
$player{"basson"} = "Andrew Vandesteeg";
$player{"flute"} = "Heidi Lawson";
$player{"oboe"} = "Jeanine Hassel";
@woodwinds = keys(%player);
@woodwindPlayers = values(%player);
# Who plays the oboe?
print("Oboe: ", $player{'oboe'}, "n");
$playerCount = scalar(@woodwindPlayers);
while (($instrument, $name) =
each(%player))
{
print( "$name plays the $instrumentn" );
}
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Pattern Matching
 A pattern is a sequence of characters to be
searched for in a character string
◦ /pattern/
 Match operators
◦ =~: tests whether a pattern is matched
◦ !~: tests whether patterns is not matched
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Pattern Matches Pattern Matches
/def/ "define" /d.f/ dif
/bdefb/ a def word /d.+f/ dabcf
/^def/ def in start of
line
/d.*f/ df, daffff
/^def$/ def line /de{1,3}f/ deef, deeef
/de?f/ df, def /de{3}f/ deeef
/d[eE]f/ def, dEf /de{3,}f/ deeeeef
/d[^eE]f/ daf, dzf /de{0,3}f/ up to deeef
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Patterns

Character Ranges
Escape
Sequence
Pattern Description
d [0-9] Any digit
D [^0-9] Anything but a digit
w [_0-9A-Za-z] Any word character
W [^_0-9A-Za-z] Anything but a word char
s [ rtnf] White-space
S [^rtnf] Anything but white-space
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Backreferences
 Memorize the matched portion of input
Use of parentheses.
◦ /[a-z]+(.)[a-z]+1[a-z]+/
◦ asd-eeed-sdsa, sd-sss-ws
◦ NOT as_eee-dfg
 They can even be accessed immediately after the
pattern is matched
◦ 1 in the previous pattern is what is matched by (.)
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Pattern Matching Options
Escape
Sequence
Description
g Match all possible patterns
i Ignore case
x Ignore white-space in pattern
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Substitutions
 Substitution operator
◦ s/pattern/substitution/options
 If $string = "abc123def";
◦ $string =~ s/123/456/
Result: "abc456def"
◦ $string =~ s/123//
Result: "abcdef"
◦ $string =~ s/(d+)/[$1]/
Result: "abc[123]def“
Use of backreference!
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Predefined Read-only
Variables
$& is the part of the string that matched the regular expression
$` is the part of the string before the part that matched
$' is the part of the string after the part that matched
EXAMPLE
$_ = "this is a sample string";
/sa.*le/; # matches "sample" within the string
# $` is now "this is a "
# $& is now "sample"
# $' is now " string"
Because these variables are set on each successful match, you should save the
values elsewhere if you
need them later in the program.
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The split and join Functions
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The split function takes a regular expression and a string, and looks for all
occurrences of the regular expression within that string. The parts of the string
that don't match the regular expression are returned in sequence as a list of
values.
The join function takes a list of values and glues them together with a glue string
between each list element.
Split Example Join Example
$line =
"merlyn::118:10:Randal:/home/merlyn
:/usr/bin/perl";
@fields = split(/:/,$line); # split $line,
using : as delimiter
# now @fields is
("merlyn","","118","10","Randal",
# "/home/merlyn","/usr/bin/perl")
$bigstring = join($glue,@list);
For example to rebuilt the password file
try something like:
$outline = join(":", @fields);

String - Pattern Examples
A simple Example
#!/usr/bin/perl
print ("Ask me a question politely:n");
$question = <STDIN>;
# what about capital P in "please"?
if ($question =~ /please/)
{
print ("Thank you for being polite!n");
}
else
{
print ("That was not very polite!n");
}
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String – Pattern Example
#!/usr/bin/perl
print ("Enter a variable name:n");
$varname = <STDIN>;
chop ($varname);
# Try asd$asdas... It gets accepted!
if ($varname =~ /$[A-Za-z][_0-9a-zA-Z]*/)
{
print ("$varname is a legal scalar variablen");
}
elsif ($varname =~ /@[A-Za-z][_0-9a-zA-Z]*/)
{
print ("$varname is a legal array variablen");
}
elsif ($varname =~ /[A-Za-z][_0-9a-zA-Z]*/)
{
print ("$varname is a legal file variablen");
}
else
{
print ("I don't understand what $varname is.n");
}
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