1. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator perl Perl is UNIX’s latest major acquisition, and one of its finest. Developed by Larry Wall, this Practical Extraction and Report Language is often hailed as the Swiss Army Office’s Knife of the UNIX System. perl is standard on Linux and also offered on Solaris. It is free, and executables are available for all UNIX flavors

2. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator perl Preliminaries A perl script or program runs in a special interpretive mode: the entire script is compiled internally in memory before it is executed. Unlike other interpreted languages like the shell, script errors are generated before execution. test whether perl is in your PATH: perl –e `print(“GNUs Not Unix\n”) :`

3. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator perl Preliminaries perl –e can do a lot of useful things from the command line perl programs are often big and are much better placed in.pl or.cgi files the sample.pl program uses the she-bang line, pointing to the perl command. perl uses the # as the comment character exactly like shell.

4. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator perl Preliminaries perl mimics awk by supporting the print and printf functions and C by terminating all statements with a semicolon perl uses the $ prefix both in the definition ($name = ), as well as in evaluation (The temperature, $name ….). perl uses to represent standard input. the printf function does not use parenthesis

5. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator perl Preliminaries If you do not provide the she-bang line (!/usr/bin/perl), then use perl sample.pl to the script chomp removes the trailing \n perl provides detailed and extensive documentation, which is accesses with the perldoc comand – try perldoc –h The newsgroup comp.lang.perl discusses problems related to perl and also posts its FAQ

6. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator Variables and Constants Variables are considered declared when they are first used. perl uses the $ prefix to identify variables both in assignment and evaluation ($x=1; print $x;) The $ prefix is also used by perl with a variable that represents an array element Variables and literals have no intrinsic type. perl understands ‘foo’, “foo” and “123” as strings, and 123, 0.0 as numeric perl makes the necessary conversions when handling expressions that use a mix of string and numeric data types

7. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator Variables and Constants for example “123” + 1 is 124; and 1 + “www” is “1www” Uninitialized variables are assumed to be null string when treated as a string and zero when treated as a number. Incrementing an uninitialized variable returns 1: $ perl –e ‘$x++ ; print(“$x\n”);’ perl is indeed unusual; it can perform computation on any string containing only letters and numbers

8. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator Variables and Constants perl is indeed unusual; it can perform computation on any string containing only letters and numbers; perl is intelligent enough to guess your intentions: $x = “A” ; $x++; $x is B $y = “P1” ; $y++ ; $y becomes P2 $z = “Q09”; $z becomes Q10

9. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator Variables and Constants Apart from the standard escape sequence, perl supports \U and \u characters $name = “steve jobs”; result = “\U$name\E”; $result is STEVE JOBS \E terminates action \U result = “\u$name\E”; $result is Steve jobs The \L and \l sequences convert string to lowercase in the same way

10. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator Operators Like all languages, the +, -, *, /, and % operators are used by perl for computation except that perl uses ** for exponentiation (2**10=1024) Apart from the comparison and logical operators, perl has two special operators for concatenation and repetition – TBD The Comparison and Logical operators =, >, !=, (returns three values; -1 if left operand is less than the right operand, 0 if equal and 1 otherwise),. (concatenates), x repeats a string

11. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator Operators if ($name eq “”) – do not use == to compare strings only numbers perl also uses logical AND and OR operators && and || if ($x 5) perl –e ‘$x=sun ; $y=“.com” ; print ($x. $y. “\n”);’ $perl –e ‘print “*” x 40;’ will display 40 *

12. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator The standard Conditional and Loops Most of the control structures used by shell and C are supported by perl. curly braces? The if conditional if ($x>1) { print(“a”); } else { print(“b”); }

13. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator The standard Conditional and Loops The if conditional if ($x > 5) { print(“a”); } elseif ($x > 3) { print(“b”); } else { print(“c”); }

14. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator The standard Conditional and Loops The if conditional printf(“”) if $x > 3

15. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator The standard Conditional and Loops The while, do-while, and for loops for ($i = 0; $i < 5; $i++) { printf(“*”); } while (1) { printf(“*”); } print(“*”) while $x++ < 5;

16. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator Reading files from Command Line Arguments The diamond, <>, is used for reading lines from a file. For example reads a line from standard input, and <> reads a line from the filename specified as arguments perl –e ‘print while (<>)’ /etc/group perl –e ‘print <>’ /etc/grouploop is implied The first use of <> is interpreted in scalar context which signifies reading one line; and the second is interpreted in list context where it represents all lines

17. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator Reading files from Command Line Arguments while (<>) can be used to read multiple files perl –e ‘print while (<>)’ foo1 foo2 foo3 perl also supports the –n option which implies the above loop perl –ne ‘print’ /etc/group perl –ne ‘print’ foo1 foo2 foo3 perl –ne ‘print if /wood\b/’ emp.lst \b is used to match on a word boundary to eliminate woodhouse and woodcook from the output

18. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator String Handling Functions chop & chomp to remove the last character of a string chomp removes only the newline index (str, substr, n) and rindex(str, substr, n) index returns the first position of the first occurrence of substr in large string str; if n is specified then n characters are skipped rindex locates the last occurence of the string

19. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator String Handling Functions reverse(str) reverses the characters and returns the reversed string substr(str1, offset, length, str2) if $x is assigned “abcdefg”, substr($x, 4, 3) returns efg $x = “abcdijklm” substr($x, 4, 0) = “efgh” $x is now abcdefghijklm

20. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator String Handling Functions substr(str1, offset, length, str2) $y = substr($x, -3, 2); $y is kl

21. second edition Your UNIX: The Ultimate Guide Das © 2006 The McGraw-Hill Companies, Inc. All rights reserved. UNIX – The Master Manipulator List and Arrays A list is a set of data An array makes the list available in a variable