Softpanorama

May the source be with you, but remember the KISS principle ;-)
Home Switchboard Unix Administration Red Hat TCP/IP Networks Neoliberalism Toxic Managers
(slightly skeptical) Educational society promoting "Back to basics" movement against IT overcomplexity and  bastardization of classic Unix

Viewing the Perl code during script execution

 

You can list any part of your program from within the Perl debugger. The following sections describe debugging commands that perform the display operations.

The l command

The simplest way to list part of your program is with the l command, which lists the next few statements in your program:

  DB<1> l
3:      $dircount = 0;
4:      $curdir = "";
5:      while (1) {
6:              # if we don't have a current directory, get one
7:              if ($curdir eq "") {
8:                      print ("Enter directory to list:\n");
9:                      $curdir = <STDIN>;
10:                     $curdir =~ s/^\s+|\s+$//g;
11:                     $curdir = &followlink($curdir);
12:                     &readsubdirs($curdir);

The l command lists a window of executable statements, which is a group of statements small enough to be easily displayed on your screen. A window usually consists of about ten statements. The line number of each statement is displayed at the beginning of its line.

NOTE
The statements displayed in today's lesson are taken from the program presented in "Week 2 in Review."

Entering the l command again displays the window of statements immediately following the last displayed line, which in this example is line 12:

  DB<1> l
13:             }
14:             $curdir = &menudir($curdir);
15:     }
16:
17:
18:     # Find all subdirectories of the given directory,
19:     # and store them in an associative array.
20:     #
21:     # The associative array subscripts and values are:
22:     # <directory name>:       1

You can specify the lines displayed by the l command. If you specify a single line number with the l command, it displays that line:

  DB<1> l 10
10:                      $curdir =~ s/^\s+|\s+$//g;

To display a range of lines, specify the first and last line number, and separate them with a hyphen:

  DB<1> l 10-15
10:                      $curdir =~ s/^\s+|\s+$//g;
11:                      $curdir = &followlink($curdir);
12:                      &readsubdirs($curdir);
13:             }
14:             $curdir = &menudir($curdir);
15:     }

To display a specified number of lines starting at a certain point, supply the starting line number, a + character, and a number of additional lines to display:

  DB<1> l 10+5
10:                      $curdir =~ s/^\s+|\s+$//g;
11:                      $curdir = &followlink($curdir);
12:                      &readsubdirs($curdir);
13:             }
14:             $curdir = &menudir($curdir);
15:     }

You also can use the l command to specify a subroutine to display. To do this, provide the name of the subroutine to display:

  DB<1> l readsubdirs
26:     sub readsubdirs {
27:             local ($dirname) = @_;
28:             local ($dirvar, $subdircount, $name, $index);
29:
30:             # open the current directory;
31:             # $dircount ensures that each file variable is unique
32:             $dirvar = "DIR" . ++$dircount;
33:             if (!opendir ($dirvar, $dirname)) {
34:                     warn ("Can't open $dirname\n");
35:                     return;

This command lists the statements in the subroutine. If the subroutine is too large to fit in a single window, only the first few statements are listed; you can list subsequent statements by entering l with no arguments.

The - Command

You can display the lines immediately preceding the last displayed line by entering the - command. For example, the following - command lists the window of lines immediately preceding the subroutine readsubdirs.

  DB<1> -
16:
17:
18:     # Find all subdirectories of the given directory,
19:     # and store them in an associative array.
20:     #
21:     # The associative array subscripts and values are:
22:     # <directory name>:       1
23:     #       (indicates that directory has been read)
24:     # <directory name>.<num>  the <num>th subdirectory
25:

Subsequent - commands go back further in the file.

The w Command

To list a window of lines containing a specified line, use the w command, and specify the number of the line to be included:

  DB<1> w 7
4:      $curdir = "";
5:      while (1) {
6:              # if we don't have a current directory, get one
7:              if ($curdir eq "") {
8:                      print ("Enter directory to list:\n");
9:                      $curdir = <STDIN>;
10:                     $curdir =~ s/^\s+|\s+$//g;
11:                     $curdir = &followlink($curdir);
12:                     &readsubdirs($curdir);
13:             }

The w command displays the three lines before the specified line and fills the window with the lines following it.

The // and ?? Commands

You can search for a line containing a particular pattern by enclosing the pattern in slashes:

  DB<1> /Find/
18:     # Find all subdirectories of the given directory,

The debugger searches forward from the last displayed line for a line matching the specified pattern. If it finds such a line, the line is displayed.

To search backward for a particular pattern, enclose the pattern in question marks:

  DB<1> ?readsubdirs?
12:                      &readsubdirs($curdir);

This command starts with the last displayed line and searches backward until it finds a line matching the specified pattern.

NOTE
Patterns specified by // and ?? can contain any special character understood by the Perl interpreter.
You optionally can omit the final / or ? character when you match a pattern.

The S Command

The S command lists all the subroutines in the current file, one subroutine per line:

  DB<> S
main::display
main::followlink
main::menudir
main::readsubdirs

Each subroutine name is preceded by the package name and a single quotation mark.



Etc

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 Hater’s 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 Technology is dominated by two types of people: those who understand what they do not manage and those who manage what they do not understand ~Archibald Putt. Ph.D


Copyright © 1996-2021 by Softpanorama Society. www.softpanorama.org was initially created as a service to the (now defunct) UN Sustainable Development Networking Programme (SDNP) without any remuneration. This document is an industrial compilation designed and created exclusively for educational use and is distributed under the Softpanorama Content License. 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 to buy a cup of coffee for authors of this site

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 Softpanorama society. We do not warrant the correctness of the information provided or its fitness for any purpose. 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.

Last modified: March, 12, 2019