2.1 Scalar data - revision numeric e-14 ( = 6.35 × )‏ operators: + (addition) - (subtraction) * (multiplication) / (division) ** (exponentiation) ++ (auto-increment) -- (auto-decrement) string double quote: print "hello\tworld"; helloworld single quote (as is): print 'hello\tworld'; hello\tworld operators:. (concatenate) x (replicate)‏

2.2 Variables - revision Always use use strict; Variable declaration my $priority; String assignment $priority = 'high'; Numerical assignment $priority = 1; Copy variable my $max = $priority; Change variable $max++; Interpolating in string my $str = "max is $max"; print variable print "$str\n"; print $str."\n"; Notes:  Variable names in Perl are case-sensitive  Give meaningful names to variables

2.3 Input & functions - revision Read line from user my $line = ; Remove "\n" (if exists) chomp $line; Length in characters length($line); Substring substr(EXPR,OFFSET,LENGTH) Note that OFFSET starts from 0. Example: my $string = "So Long, and Thanks for All the Fish"; my $sub = substr($string,1,4); print $sub; o Lo

2.4 Comments on exercises Always run your script with “ perl -w ” and take care of all warnings  submitted scripts should not produce any warnings When you us problems you run into, send the script, and copy the running of it (with “ perl -w ”) and the output from the command prompt window When submitting exercises by write your name and the exercise number in the subject line (for example “ Shmulik Israeli perl ex. 2 ”) Write a separate file for each question, and name the scripts: “ ex2.1.pl ”, “ ex2.2.pl ”, “ ex2.3.pl ”…

2.5 Comments on exercises Use meaningful names for variables. We always add " use strict; " in the first line of scripts (once is enogh). Always declare variables using " my $newVarName; ". Use chomp function to omit newline ( "\n" ) from input.

2.6 Comments on exercises Mind the input (parameters given by user) and the arguments (parameters used by functions): The last question (Q5) was somewhat tricky… The parameters of substr are: 1) string 2) start 3) LENGTH and in the exercise the request was that the numbers will be 1) start 2) stop 3) duplications So you should use the STOP provided by the user and manipulate it to get the LENGTH that the substr function uses: (LENGTH = STOP – START + 1)

2.7 Adding comments Comments: The # symbol, and anything from it to the end of the line is ignored. # get start and stop values from the user my $start = my $stop = # calculate string length my $length = $start - $stop + 1;

2.8 Adding comments Comments: If you want to insert a comment of multiple lines, you can use =begin and =cut. =begin This program prints stuff. Here you can write any text you want and you don’t need any # =cut print "stuff\n";

2.9 Uninitialized variables If uninitialized variables are used (before assignment) a warning is issued: my $a; print($a+3); Use of uninitialized value in addition (+) 3 print("a is :$a:"); Use of uninitialized value in concatenation (.) or string a is ::

2.10 Lesson 2: Lists and Arrays

3 2 * 2 1"fred" Lists and arrays A list is an ordered set of scalar values: (3,2,1,"fred") An array is a variable that holds a list: = (3,2,1,"fred"); You can access an individual array element: print $arr[1];2 $arr[0] = "*"; 3 2 1"fred"

2.12 Lists and arrays You can easily get a sub-array: = (3,2,1,"fred","bob"); 321fredbob print $arr[1]; 2 You can extend an array as much as you like: = ("A","B","C") $arr2[5] = 3 2 1"fred" "bob" "fred" 0 "A""A""B""B" "F""F" undef "A""A""B""B" "C""C"

2.13 Lists and arrays Assigning to arrays: = (3..6);# same Multiple assignment: my ($a,$b) = ('cow','dog'); $a='cow'; $b='dog'; my = (1..5);$a=1; scalar - counting array elements: print 4 Last element index: print $#arr; 3

2.14 Arrays in scalar context Consider the following: = ('a','b','c','d'); my $num = $#arr; $num = 3 my $num $num = 4 my ($num1, $second) $num1 = 'a' $second = 'b' This one will be very useful in the future

2.15 Interpolating arrays You can interpolate arrays and array elements into strings: = ("a","b","cat",d"); abcatd print a b cat d print "$arr[2] is the third element of cat is the third element

2.16 Reading arrays You can read lines from the standard input in list context: = ; will store all the lines entered until the user hits ctrl-z. ctrl-z to indicate end of "cogito\n""ergo\n""sum\n"

2.17 Reading arrays chomp will work on entrie arrays: = ; "cogito""ergo""sum"

2.18 Manipulating arrays – push & pop = ('a','b','c','d','e'); = ('a','b','c','d','e'); my $num = print $num;e e f a b c d $num

2.19 shift & unshift = ('a','b','c'); my $num = print $num;a = ('a','b','c');

2.20 split & join my = split(/ /, "You talkin to me? You talkin to = = split(//, "You talkin to me? You talkin to = ("Y","o","u"," ","t","a","l","k","i","n"," ",...) my $str = print "$str\n"; "You-talkin-to-me?-You-talkin-to-me?"

2.21 Reversing lists = ("yossi","bracha","moshe"); = print moshe;bracha;yossi

2.22 Sorting lists Default sorting is alphabetical: = sort("yossi","bracha","moshe"); is ("bracha","moshe","yossi") = sort(1,3,9,81,243); is (1,243,3,81,9) Other forms of sorting require subroutine definition: = sort(compare_sub 1,3,9,81,243); We might get to that latter… Note: sort and reverse do not change the array. They return a new array after the operation of the function (that should be saved in another array if needed for further use).

2.23 Class exercise Read a number from the first line of input, and then read the rest of the lines into an array (stop by using ctrl-z). Print the line selected by the number provided in the first line. 2.Read a list of numbers separated by spaces, and print those numbers in reverse order, separated by slashes (/). 3.Read a list of words separated by spaces, sort and print them. 4.Like in 3, but return only the last word (after the sorting). 5.Like in 3, but reverse the order of the letters of the last word

It is possible to pass arguments to Perl from the command line. These Command-line arguments are stored in an array created automatically : use strict; my $joinedArr = print "Hi" "man" 5

It is possible to pass arguments to Perl from the command line. These Command-line arguments are stored in an array created automatically : use strict; my $joinedArr = print "Hi man"5

2.26 Class exercise Read a list of numbers from the command-line and print those numbers in reverse order, separated by slashes (/). 2.Read a list of words from the command-line, sort and print them. 3.Like in 2, but return only the last word (after the sorting). 4.Like in 2, but reverse the order of the letters of the last word