Programming in Perl●Introduction●Scalars●Lists and Arrays●Control Structures●I/O●Hashes●Regular Expressions●Dealing with Files●Subroutines●Directory and File ManipulationHistory●Perl stands for Practical Extraction and Report Language.●Created by Larry Wall in the mid 1980s.●Released to Usenet readers and became popular.●Perl is free for use and is distributed under the GNU public license.Advantages of Perl●Fills the gap between programming in a conventional compiled language and shell programming.●Is very high-level. A typical Perl program may take 30% to 70% as much code as a C program.●Good for accomplishing quick tasks and primarily for text manipulation.Perl Is Interpreted●Your Perl program is initially compiled into bytecodes when you invoke your program and these bytecodes are then interpreted.●Similar in some ways to Java.●Faster than shell interpretation.●Still much slower than conventionally compiled programs.Sample Perl Program ●First line indicates the name of the program that executes the file. Can execute this file like a shell script. The -w means to print warnings.●Second line is a comment.●Third line is a pragma to indicate that variables should be declared and strings should be quoted.●Fourth line prints the string.●Last line exits the program. #!/usr/bin/perl -w use strict; # This line will print a hello world message. print “Hello world!\n”; exit 0;Basic Concepts●No main function, but can have subroutines.●Many features taken from C and shell commands.●Easy to write a program with a few commands to perform simple tasks. Features Similar to C●Many operators.●Many control structures.●Supports formatted I/O.●Can access command line arguments.●Supports using standard input, output, and error.Features Similar to Shell Programming●Comments: # to the end of the line●$variables●Interpolation of variables in “strings”.●Support for command line arguments.●Implicit conversions between strings and numbers.●Support for regular expressions.●Some control structures.●Many specific operators similar to shell commands or Unix utilities.Scalar Data●Scalars represent a single value.●Scalar types:–Strings–Numbers●Strings and numbers, like in the shell, are used almost interchangeably in Perl.Numbers●Perl stores all numbers as double-precision values internally.●Numeric Literals–floating-point literals–integer literals●decimal integer literals●non-decimal integer literalsFloating-Point Literals●Floating-point literals (or constants) in Perl are similar to those in C.●All of the following represent the same value.149.567149567e-31.49567E20.0149567e4Decimal Integer Literals●Similar to C.0 -54 511●Can use underscores for large values.28396838762_839_683_876Nondecimal Integer Literals●Similar to C.0177 # literals beginning with zero# are octol constants0x7f # literals beginning with 0x # are hexadecimal constants●Not found in C.0b1111111 # literals beginning with 0b # are binaryOperators Similar to C●assignment: =●arithmetic: +, -, *, /, %●bitwise: &, |, ^, ~, <<, >>●relational: <, <=, ==, !=, >=, >●logical: &&, ||, !●binary asg: +=, -=, *=, ...●Increment: ++, --●Ternary: ?:Operators Different from C●** # exponentiation●<=> # numeric comparison●=~, !~ # match operators●x # string repetition●. # string concatenation●eq,ne,lt,gt,le,ge # string relational●cmp # string comparison●\,, => # listStrings●Unlike many conventional programming languages, string is a basic type in Perl.●String Literals–single-quoted strings–double-quoted stringsSingle-Quoted Strings●Use single-quoted strings when you do not want variables to be interpolated.●Can use the '\' character to indicate that a single quote is part of the string ('...\'...') or a backslash is part of the string ('...\\...').●The '\' followed by any other character is just a regular '\'.'Hello World!''This is just a \ character.''Whalley\'s Class''\'''The \\ is used to access directories in DOS.'Double-Quoted Strings●Double-quoted strings are similar to C in that you can use the backslash to specify a special character.“This line ends with a newline.\n”“These\twords\tare\tseparated\tby\ttabs.”“The \”title\” of a book should be quoted.”“The price is \$1,000.”●Double-quoted strings can also be used to interpolate variables, as in the Bourne shell.String Operators●'.' is used for string concatenation.“One string can be concatenated ” . “with another.”'The price is $1,000.' . “\n”●'x' is used for string repetition.“double” x 2 eq “doubledouble”“ ” x 10 # means 10 blanks in a row. Implicit Conversions between Strings and Numbers●Implicit conversions are performed depending on the operator that is used. The coercions are performed without any warnings.9 x “5” # “99999”“1” + “2” # 3“45” - 1 . 7 # “447”Scalar Variables●Scalar variable names are preceded by '$'. Unlike shell variables, a '$' is always used.●General form.$[A-Za-z_][A-Za-z_0-9]*●Scalars can hold both strings and numbers.Declaring Scalar Variables●If you use the following pragma:use strict; then all variables must be declared. You can do this with the my operator.●General form. Use the first form to declare one variable. Use the second form to declare multiple variables.my <variable_name>;my (<variable_name>, ..., <variable_name>);●Variable declarations can go anywhere, but are often placed at the top of the program.Example Scalar Variable Declarationsmy $sum; # used to hold a sum of valuesmy ($i, $j, $k); # counter variablesmy $line; # contains a line of textmy $n = 0; # variable with an initial valuemy $s = “”; # another variable with an initial # valuemy $a = $b; # variables can be initialized to # have a run-time valueInterpolation of Variables in Strings●Variables are interpolated inside double-quoted strings. Say the value of $n is 7. The string “The value of \$n is: $n.\n” would be interpolated to be:“The value of $n is: 7.\n”●One can use the form: ${name} when the variable is followed by a character in a string that could be part of an identifier. Say the value of $day is “Tues”. The string“Today is ${day}day.\n” would be interpolated to be:“Today is Tuesday.\n”Assigning Scalar Values●The assignment operator is '=', which is the same operator that is