Softpanorama
May the source be with you, but remember the KISS principle ;-)

Contents Bulletin Scripting in shell and Perl Network troubleshooting History Humor

Introduction to Perl 5.10 for Unix System Administrators

(Perl 5.10 without excessive complexity)

by Dr Nikolai Bezroukov

Contents : Foreword : Ch01 : Ch02 : Ch03 : Ch04 : Ch05 : Ch06 : Ch07 : Ch08 :


Prev | Up | Contents | Down | Next

5.8. Summary

Two general observation:

To be successful you need to use to adopt some elements of style that makes mistakes less probable:

Below are some reference tables from Medinets book: 

 Regular Expression Meta-Characters, Meta-Brackets, and Meta-Sequences

Meta
Character

Description

^ This meta-character - the caret - will match the beginning of a string or if the /m option is used, matches the beginning of a line. It is one of two pattern anchors - the other anchor is the $.
. This meta-character will match any character except for the newline unless the /s option is specified. If the /s option is specified, then the newline will also be matched.
$ This meta-character will match the end of a string or if the /m option is used, matches the end of a line. It is one of two pattern anchors - the other anchor is the ^.
| This meta-character - called alternation - lets you specify two values that can cause the match to succeed. For instance, m/a|b/ means that the $_ variable must contain the "a" or "b" character for the match to succeed.
* This meta-character indicates that the "thing" immediately to the left should be matched 0 or more times in order to be evaluated as true.
+ This meta-character indicates that the "thing" immediately to the left should be matched 1 or more times in order to be evaluated as true.
? This meta-character indicates that the "thing" immediately to the left should be matched 0 or 1 times in order to be evaluated as true. When used in conjunction with the +, _, ?, or {n, m} meta- characters and brackets, it means that the regular expression should be non-greedy and match the smallest possible string.

 
Meta
Brackets
Description
() The parentheses let you affect the order of pattern evaluation and act as a form of pattern memory.
(?...) If a question mark immediately follows the left parentheses, it indicates that an extended mode component is being specified.
{n, m} The curly braces let specify how many times the "thing" immediately to the left should be matched. {n} means that it should be matched exactly n times. {n,} means it must be matched at least n times. {n, m} means that it must be matched at least n times and not more than m times.
[] The square brackets let you create a character class. For instance, m/[abc]/ will evaluate to true if any of "a", "b", or "c" is contained in $_. The square brackets are a more readable alternative to the alternation meta-character.

 
Meta
Sequences
Description
\ This meta-character "escapes" the following character. This means that any special meaning normally attached to that character is ignored. For instance, if you need to include a dollar sign in a pattern, you must use \$ to avoid Perl's variable interpolation. Use \\ to specify the backslash character in your pattern.
\0nnn Any Octal byte.
\A This meta-sequence represents the beginning of the string. Its meaning is not affected by the /m option.
\b This meta-sequence represents the backspace character inside a character class; otherwise, it represents a word boundary. A word boundary is the spot between word (\w) and non-word(\W) characters. Perl thinks that the \W meta-sequence matches the imaginary characters off the ends of the string.
\B Match a non-word boundary.
\cn Any control character.
\d Match a single digit character.
\D Match a single non-digit character.
\e Escape.
\E Terminate the \L or \U sequence.
\f Form Feed.
\G Match only where the previous m//g left off.
\l Change the next character to lowercase.
\L Change the following characters to lowercase until a \E sequence is encountered.
\n Newline.
\Q Quote Regular Expression meta-characters literally until the \E sequence is encountered.
\r Carriage Return.
\s Match a single whitespace character.
\S Match a single non-whitespace character.
\t Tab.
\u Change the next character to uppercase.
\U Change the following characters to uppercase until a \E sequence is encountered.
\v Vertical Tab.
\w Match a single word character. Word characters are the alphanumeric and underscore characters.
\W Match a single non-word character.
\xnn Any Hexadecimal byte.
\Z This meta-sequence represents the end of the string. Its meaning is not affected by the /m option.
 

Regular Expressions form almost a 'language within a language' in Perl. As you can see above, they can be fairly involved, and (lets face it) if you are not familiar with them now, you are not going to learn them without practice. Therefore, we suggest the following path for learning regular expressions.

More about  Modifiers

The matching operator has several options. The most useful option is probably the capability to ignore case (option i) and to iterate throuth all matches in a string (option g).

Options for the Matching Operator

Option Description
g This option finds all occurrences of the pattern in the string. You can iterate over the matches using a loop statement or put result into array
i This option ignores the case of characters in the string.
m This option treats the string as multiple lines. Perl does some optimization by assuming that $_ contains a single line of input. If you know that it contains multiple newline characters, use this option to turn off the optimization.
o This option compiles the pattern only once. You can achieve some small performance gains with this option. It should be used with variable interpolation only when the value of the variable will not change during the lifetime of the program.
s This option treats the string as a single line.
x This option lets you use extended regular expressions. Basically, this means that Perl will ignore whitespace that's not escaped with a backslash or within a character class. I highly recommend this option so you can use spaces to make your regular expressions more readable. See the section "Example: Extension Syntax" later in this chapter for more information.

Modifiers

The matching operator has several options. The most useful option is probably the capability to ignore case (option i) and to iterate throuth all matches in a string (option g).

Options for the Matching Operator

Option Description
g This option finds all occurrences of the pattern in the string. You can iterate over the matches using a loop statement or put result into array
i This option ignores the case of characters in the string.
m This option treats the string as multiple lines. Perl does some optimization by assuming that $_ contains a single line of input. If you know that it contains multiple newline characters, use this option to turn off the optimization.
o This option compiles the pattern only once. You can achieve some small performance gains with this option. It should be used with variable interpolation only when the value of the variable will not change during the lifetime of the program.
s This option treats the string as a single line.
x This option lets you use extended regular expressions. Basically, this means that Perl will ignore whitespace that's not escaped with a backslash or within a character class. I highly recommend this option so you can use spaces to make your regular expressions more readable. See the section "Example: Extension Syntax" later in this chapter for more information.

Prev | Up | Contents | Down | Next



Etc

FAIR USE NOTICE This site contains copyrighted material the use of which has not always been specifically authorized by the copyright owner. We are making such material available in our efforts to advance understanding of environmental, political, human rights, economic, democracy, scientific, and social justice issues, etc. We believe this constitutes a 'fair use' of any such copyrighted material as provided for in section 107 of the US Copyright Law. In accordance with Title 17 U.S.C. Section 107, the material on this site is distributed without profit exclusivly for research and educational purposes.   If you wish to use copyrighted material from this site for purposes of your own that go beyond 'fair use', you must obtain permission from the copyright owner. 

ABUSE: IPs or network segments from which we detect a stream of probes might be blocked for no less then 90 days. Multiple types of probes increase this period.  

Society

Groupthink : Two Party System as Polyarchy : Corruption of Regulators : Bureaucracies : Understanding Micromanagers and Control Freaks : Toxic Managers :   Harvard Mafia : Diplomatic Communication : Surviving a Bad Performance Review : Insufficient Retirement Funds as Immanent Problem of Neoliberal Regime : PseudoScience : Who Rules America : Neoliberalism  : The Iron Law of Oligarchy : Libertarian Philosophy

Quotes

War and Peace : Skeptical Finance : John Kenneth Galbraith :Talleyrand : Oscar Wilde : Otto Von Bismarck : Keynes : George Carlin : Skeptics : Propaganda  : SE quotes : Language Design and Programming Quotes : Random IT-related quotesSomerset Maugham : Marcus Aurelius : Kurt Vonnegut : Eric Hoffer : Winston Churchill : Napoleon Bonaparte : Ambrose BierceBernard Shaw : Mark Twain Quotes

Bulletin:

Vol 25, No.12 (December, 2013) Rational Fools vs. Efficient Crooks The efficient markets hypothesis : Political Skeptic Bulletin, 2013 : Unemployment Bulletin, 2010 :  Vol 23, No.10 (October, 2011) An observation about corporate security departments : Slightly Skeptical Euromaydan Chronicles, June 2014 : Greenspan legacy bulletin, 2008 : Vol 25, No.10 (October, 2013) Cryptolocker Trojan (Win32/Crilock.A) : Vol 25, No.08 (August, 2013) Cloud providers as intelligence collection hubs : Financial Humor Bulletin, 2010 : Inequality Bulletin, 2009 : Financial Humor Bulletin, 2008 : Copyleft Problems Bulletin, 2004 : Financial Humor Bulletin, 2011 : Energy Bulletin, 2010 : Malware Protection Bulletin, 2010 : Vol 26, No.1 (January, 2013) Object-Oriented Cult : Political Skeptic Bulletin, 2011 : Vol 23, No.11 (November, 2011) Softpanorama classification of sysadmin horror stories : Vol 25, No.05 (May, 2013) Corporate bullshit as a communication method  : Vol 25, No.06 (June, 2013) A Note on the Relationship of Brooks Law and Conway Law

History:

Fifty glorious years (1950-2000): the triumph of the US computer engineering : Donald Knuth : TAoCP and its Influence of Computer Science : Richard Stallman : Linus Torvalds  : Larry Wall  : John K. Ousterhout : CTSS : Multix OS Unix History : Unix shell history : VI editor : History of pipes concept : Solaris : MS DOSProgramming Languages History : PL/1 : Simula 67 : C : History of GCC developmentScripting Languages : Perl history   : OS History : Mail : DNS : SSH : CPU Instruction Sets : SPARC systems 1987-2006 : Norton Commander : Norton Utilities : Norton Ghost : Frontpage history : Malware Defense History : GNU Screen : OSS early history

Classic books:

The Peter Principle : Parkinson Law : 1984 : The Mythical Man-MonthHow to Solve It by George Polya : The Art of Computer Programming : The Elements of Programming Style : The Unix Haterís Handbook : The Jargon file : The True Believer : Programming Pearls : The Good Soldier Svejk : The Power Elite

Most popular humor pages:

Manifest of the Softpanorama IT Slacker Society : Ten Commandments of the IT Slackers Society : Computer Humor Collection : BSD Logo Story : The Cuckoo's Egg : IT Slang : C++ Humor : ARE YOU A BBS ADDICT? : The Perl Purity Test : Object oriented programmers of all nations : Financial Humor : Financial Humor Bulletin, 2008 : Financial Humor Bulletin, 2010 : The Most Comprehensive Collection of Editor-related Humor : Programming Language Humor : Goldman Sachs related humor : Greenspan humor : C Humor : Scripting Humor : Real Programmers Humor : Web Humor : GPL-related Humor : OFM Humor : Politically Incorrect Humor : IDS Humor : "Linux Sucks" Humor : Russian Musical Humor : Best Russian Programmer Humor : Microsoft plans to buy Catholic Church : Richard Stallman Related Humor : Admin Humor : Perl-related Humor : Linus Torvalds Related humor : PseudoScience Related Humor : Networking Humor : Shell Humor : Financial Humor Bulletin, 2011 : Financial Humor Bulletin, 2012 : Financial Humor Bulletin, 2013 : Java Humor : Software Engineering Humor : Sun Solaris Related Humor : Education Humor : IBM Humor : Assembler-related Humor : VIM Humor : Computer Viruses Humor : Bright tomorrow is rescheduled to a day after tomorrow : Classic Computer Humor

The Last but not Least


Copyright © 1996-2016 by Dr. Nikolai Bezroukov. www.softpanorama.org was created as a service to the UN Sustainable Development Networking Programme (SDNP) in the author free time. This document is an industrial compilation designed and created exclusively for educational use and is distributed under the Softpanorama Content License.

The site uses AdSense so you need to be aware of Google privacy policy. You you do not want to be tracked by Google please disable Javascript for this site. This site is perfectly usable without Javascript.

Original materials copyright belong to respective owners. Quotes are made for educational purposes only in compliance with the fair use doctrine.

FAIR USE NOTICE This site contains copyrighted material the use of which has not always been specifically authorized by the copyright owner. We are making such material available to advance understanding of computer science, IT technology, economic, scientific, and social issues. We believe this constitutes a 'fair use' of any such copyrighted material as provided by section 107 of the US Copyright Law according to which such material can be distributed without profit exclusively for research and educational purposes.

This is a Spartan WHYFF (We Help You For Free) site written by people for whom English is not a native language. Grammar and spelling errors should be expected. The site contain some broken links as it develops like a living tree...

You can use PayPal to make a contribution, supporting development of this site and speed up access. In case softpanorama.org is down you can use the at softpanorama.info

Disclaimer:

The statements, views and opinions presented on this web page are those of the author (or referenced source) and are not endorsed by, nor do they necessarily reflect, the opinions of the author present and former employers, SDNP or any other organization the author may be associated with. We do not warrant the correctness of the information provided or its fitness for any purpose.

Last modified: July 07, 2013