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Serialsing and unserialising data for storage and transfer in Perl

If you want to save a series of strings to a file, or pass them over a network connection, you'll need to delimit them - add in a special character so that the receiving / reading program will know where one piece of data ends and the next starts. The problem comes if the chosen special character may appear in the string, and how to tell the receiver which the real end is. The process of manipulating the incoming character string so that it can be transferred / saved is known as serialisation.

One of the common ways of serialising data is to add \ characters in front of "specials", but that becomes a bit of an issue if the string includes control codes. Another way is to use "URL encoding" where special characters are replaced by a % character followed by 2 hex digits. That works for any ASCII character, and also has the advantages that it's a familiar format to many people, that words and numbers are still readable, and that the stored / transferred string isn't that much longer than the original. One of the other thing about a serialisation algorithm is that it must be easily reversed - again, that's true for URL encoding.

I was discussing how to do URL encoding and decoding in Perl today (on a Tcl course during a coffee break, but that's another story) and my complete demonstration is [here]. And, being Perl, both encoding and decoding are very short - one line - algorithms.

Encoding:
  $serialised =~ s/([^\w])/"%".sprintf("%02x",ord($1))/eg;
Decoding:
  $reverted =~ s/%(..)/pack("C",hex($1))/eg;


Running that code within a sample program:

  munchkin:ftcl grahamellis$ perl itsperl
  'We love C++!' said George
  %27We%20love%20C%2b%2b%21%27%20said%20George%0a
  'We love C++!' said George
  munchkin:ftcl grahamellis$

(written 2012-02-28, updated 2012-03-10)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
P212 - Perl - More on Character Strings
  [4452] Binary data handling - Python and Perl - (2015-03-09)
  [3927] First match or all matches? Perl Regular Expressions - (2012-11-19)
  [3707] Converting codons via Amino Acids to Proteins in Perl - (2012-04-25)
  [3650] Possessive Regular Expression Matching - Perl, Objective C and some other languages - (2012-03-12)
  [3546] The difference between dot (a.k.a. full stop, period) and comma in Perl - (2011-12-09)
  [3411] Single and double quotes strings in Perl - what is the difference? - (2011-08-30)
  [3332] DNA to Amino Acid - a sample Perl script - (2011-06-24)
  [3322] How much has Perl (and other languages) changed? - (2011-06-10)
  [3100] Looking ahead and behind in Regular Expressions - double matching - (2010-12-23)
  [3059] Object Orientation in an hour and other Perl Lectures - (2010-11-18)
  [2993] Arrays v Lists - what is the difference, why use one or the other - (2010-10-10)
  [2877] Further more advanced Perl examples - (2010-07-19)
  [2874] Unpacking a Perl string into a list - (2010-07-16)
  [2834] Teaching examples in Perl - third and final part - (2010-06-27)
  [2801] Binary data handling with unpack in Perl - (2010-06-10)
  [2657] Want to do a big batch edit? Nothing beats Perl! - (2010-03-01)
  [2379] Making variables persistant, pretending a database is a variable and other Perl tricks - (2009-08-27)
  [2230] Running a piece of code is like drinking a pint of beer - (2009-06-11)
  [1947] Perl substitute - the e modifier - (2008-12-16)
  [1735] Finding words and work boundaries (MySQL, Perl, PHP) - (2008-08-03)
  [1727] Equality and looks like tests - Perl - (2008-07-29)
  [1510] Handling Binary data (.gif file example) in Perl - (2008-01-17)
  [1336] Ignore case in Regular Expression - (2007-09-08)
  [1305] Regular expressions made easy - building from components - (2007-08-16)
  [1251] Substitute operator / modifiers in Perl - (2007-06-28)
  [1230] Commenting a Perl Regular Expression - (2007-06-12)
  [1222] Perl, the substitute operator s - (2007-06-08)
  [943] Matching within multiline strings, and ignoring case in regular expressions - (2006-11-25)
  [928] C++ and Perl - why did they do it THAT way? - (2006-11-16)
  [737] Coloured text in a terminal from Perl - (2006-05-29)
  [608] Don't expose your regular expressions - (2006-02-15)
  [597] Storing a regular expression in a perl variable - (2006-02-09)
  [586] Perl Regular Expressions - finding the position and length of the match - (2006-02-02)
  [583] Remember to process blank lines - (2006-01-31)
  [453] Commenting Perl regular expressions - (2005-09-30)


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