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For 2021 - online Python 3 training - see ((here)).

Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
We can now offer tailored online training - small groups, real tutors - works really well for groups of 4 to 14 delegates. Anywhere in the world; course language English.

Please ask about private 'maintenance' training for Python 2, Tcl, Perl, PHP, Lua, etc.
Binary data handling with unpack in Perl

During today's Perl course, I was asked to provide an example of the unpack function for extracting multiple values from a piece of data - typically binary data extracted from a file into a scalar variable.


Dorothy-2:de$ perl imgsize sd*.gif
sd1.gif is GIF, 89a, 450 by 250
sd2.gif is GIF, 89a, 250 by 300
sd3.gif is GIF, 89a, 300 by 250
sd4.gif is GIF, 89a, 333 by 333
Dorothy-2:de$



And what better images to illustrate the article that ones of the delegates on the course?


Here's the program:

for $file(@ARGV) {
  open (FH,$file);
  read (FH,$header,10);
  ($type,$st,$wid,$hei) = unpack("a3a3vv",$header);
  print ("$file is $type, $st, $wid by $hei\n");
}


From memory (!) I recalled that a .gif file starts with 3 bytes to confirm that it's a GIF file, 3 bytes to tell us which subformat has been used, and 2 2-byte 16 bit unsigned integers, bigendian, which tell the width and height of the image in pixels.

You'll notice that the course had a lot of delegate on it. Where there's a high number of delegates, all at a similar level, all from the same company, and all doing similar applications, I will let the customer place up to 20 delegates on a course. Where the delegates background differs, I request a reduced top number. And on a public course, where people from differnt companies book, we restrict delegates to just 8 so that there's a good opportunity for the tutor to talk to each and every delegate about their own individual use of the subject being taught.


P.S. There's another example of unpack on a .gif file - [here] - that I wrote a wile back; the techniques used are slightly different, and the program is one that came from a series named after British Rivers - in this case the Ystwyth from Aberystwyth fame.

(written 2010-06-10)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
P212 - Perl - More on Character Strings
  [453] Commenting Perl regular expressions - (2005-09-30)
  [583] Remember to process blank lines - (2006-01-31)
  [586] Perl Regular Expressions - finding the position and length of the match - (2006-02-02)
  [597] Storing a regular expression in a perl variable - (2006-02-09)
  [608] Don't expose your regular expressions - (2006-02-15)
  [737] Coloured text in a terminal from Perl - (2006-05-29)
  [928] C++ and Perl - why did they do it THAT way? - (2006-11-16)
  [943] Matching within multiline strings, and ignoring case in regular expressions - (2006-11-25)
  [1222] Perl, the substitute operator s - (2007-06-08)
  [1230] Commenting a Perl Regular Expression - (2007-06-12)
  [1251] Substitute operator / modifiers in Perl - (2007-06-28)
  [1305] Regular expressions made easy - building from components - (2007-08-16)
  [1336] Ignore case in Regular Expression - (2007-09-08)
  [1510] Handling Binary data (.gif file example) in Perl - (2008-01-17)
  [1727] Equality and looks like tests - Perl - (2008-07-29)
  [1735] Finding words and work boundaries (MySQL, Perl, PHP) - (2008-08-03)
  [1947] Perl substitute - the e modifier - (2008-12-16)
  [2230] Running a piece of code is like drinking a pint of beer - (2009-06-11)
  [2379] Making variables persistant, pretending a database is a variable and other Perl tricks - (2009-08-27)
  [2657] Want to do a big batch edit? Nothing beats Perl! - (2010-03-01)
  [2834] Teaching examples in Perl - third and final part - (2010-06-27)
  [2874] Unpacking a Perl string into a list - (2010-07-16)
  [2877] Further more advanced Perl examples - (2010-07-19)
  [2993] Arrays v Lists - what is the difference, why use one or the other - (2010-10-10)
  [3059] Object Orientation in an hour and other Perl Lectures - (2010-11-18)
  [3100] Looking ahead and behind in Regular Expressions - double matching - (2010-12-23)
  [3322] How much has Perl (and other languages) changed? - (2011-06-10)
  [3332] DNA to Amino Acid - a sample Perl script - (2011-06-24)
  [3411] Single and double quotes strings in Perl - what is the difference? - (2011-08-30)
  [3546] The difference between dot (a.k.a. full stop, period) and comma in Perl - (2011-12-09)
  [3630] Serialsing and unserialising data for storage and transfer in Perl - (2012-02-28)
  [3650] Possessive Regular Expression Matching - Perl, Objective C and some other languages - (2012-03-12)
  [3707] Converting codons via Amino Acids to Proteins in Perl - (2012-04-25)
  [3927] First match or all matches? Perl Regular Expressions - (2012-11-19)
  [4452] Binary data handling - Python and Perl - (2015-03-09)

G401 - Well House Consultants - On Site courses
  [139] Just provide a room and the students - (2004-12-03)
  [191] Setting up a training room for a course - (2005-01-27)
  [213] Off to Munich - (2005-02-13)
  [241] Dress for training - (2005-03-10)
  [382] Central London Courses - Perl, PHP, Python, Tcl, MySQL - (2005-07-18)
  [438] Fair system for travel and accommodation expenses - (2005-09-07)
  [439] You cant - (2005-09-08)
  [1027] Cue the music, I'm happy. - (2007-01-09)
  [1465] Perl, PHP, Python, Tcl, Linux, MySQL, Ruby courses ... - (2007-12-09)
  [1600] Cambidge - Tcl, Expect and Perl courses - (2008-04-04)
  [1781] Reception - (2008-09-01)
  [2041] httpd, Tomcat and PHP course enhancements - (2009-02-14)
  [2309] Lua training class in Spanish - (2009-07-29)
  [2311] Floor to ceiling - (2009-07-30)
  [2810] A course review - for the tutor to complete - (2010-06-14)
  [2928] Public (scheduled) or private course? Book direct, or through a third party? - (2010-08-19)
  [2956] On site course - travel and accommodation expenses - (2010-09-14)
  [3131] Lua, Tcl, Python; Worldwide training classes - (2011-01-14)
  [3137] Training Classes - should the training company provide a system for each delegate to use? - (2011-01-18)
  [3691] Back in Cambridge to give a Lua course - (2012-04-09)
  [3715] Changing face - Filton - (2012-05-01)
  [3898] The course must go on - improvements to tutor travel plans, with immediate effect - (2012-10-17)
  [3950] 10 reasons why I travel the night before a course starts - (2012-12-10)
  [4132] Using your own laptop on our courses - now even easier! - (2013-07-05)
  [4230] Well House Consultants - course prices for 2014 - (2013-12-26)
  [4602] Training course and hotel room prices - 2016 - (2015-12-31)
  [4739] A year of changes for Lisa and Graham Ellis, and Well House - (2017-05-27)
  [4769] Python, Tcl, Lua and other Open Source programming courses for 2018 - (2017-12-31)


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After the Perl course in Nurnberg
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How are you getting on?
Regular Expression Myths
Travelling across Europe
After the Perl course in Nurnberg
Binary data handling with unpack in Perl
The Merchants And
Nuremberg - some pictures
Perl - skip the classics and use regular expressions
Sur la T.G.V.
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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