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Single and double quotes strings in Perl - what is the difference?

In Perl, there's usually more than one way of doing it ...

If you're writing a string of text into your program, your first possibility is to use single quotes - in which case you're writing a literal string with everything between the single quote chartacters included exactly in the string. And your second possibility is to use double quotes - which are actually an operator, and \ $ and @ characters within the string trigger "escaping" of the following characters, and inclusion of variable contents.

Here's some code to show that:

  $name = Bob;
  @choice = ("Tea",'Coffee');
 
  print 'Here is $name choosing from @choice\n';
  print "\n";
  print "Here is $name choosing from @choice\n";


And that runs as follows:

  munchkin:ap3 grahamellis$ perl asy
  Here is $name choosing from @choice\n
  Here is Bob choosing from Tea Coffee
  munchkin:ap3 grahamellis$


If you really want to include a " within a "'d string, you can use \", but you shouldn't be able to use the same technique to include a ' within a 'd string (in practise, there's an exception made that lets you do so!!). However, all this extra quoting of delimiters gets messy so you can choose your own special characters as the delimiter using the qq notation for a double quoted string and the q notation for a single quoted string:

  $name = Bob;
  @choice = (qq!Tea!,q%Coffee%);
 
  print q#Here is $name choosing from @choice\n#;
  print qq"\n";
  print qq(Here is $name choosing from @choice\n);


Output is identical to what you saw just above. Just about any special character may be used - even the # which is normally used for comments; if you use an open bracket or brace, then the closing character should be the opposing bracket of brace - otherwise the close is the same as the open. And your choice of special character only lasts for the one string.

Want still more flexibilty? You can use a "here document" where the delimiter used is an entire word of your choice! There's a previous article about here documents ... [here] ;-).
(written 2011-08-30)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
P205 - Perl - Initial String Handling
  [3770] Sample answers to training course exercises - available on our web site - (2012-06-21)
  [3548] Dark mornings, dog update, and Python and Lua courses before Christmas - (2011-12-10)
  [3547] Using Perl to generate multiple reports from a HUGE file, efficiently - (2011-12-09)
  [3005] Lots of ways of doing it in Perl - printing out answers - (2010-10-19)
  [2963] Removing the new line with chop or chomp in Perl - what is the difference? - (2010-09-21)
  [2832] Are you learning Perl? Some more examples for you! - (2010-06-27)
  [2816] Intelligent Matching in Perl - (2010-06-18)
  [2798] Perl - skip the classics and use regular expressions - (2010-06-08)
  [1860] Seven new intermediate Perl examples - (2008-10-30)
  [1849] String matching in Perl with Regular Expressions - (2008-10-20)
  [1608] Underlining in Perl and Python - the x and * operator in use - (2008-04-12)
  [1195] Regular Express Primer - (2007-05-20)
  [987] Ruby v Perl - interpollating variables - (2006-12-15)
  [970] String duplication - x in Perl, * in Python and Ruby - (2006-12-07)
  [324] The backtick operator in Python and Perl - (2005-05-25)
  [254] x operator in Perl - (2005-03-22)
  [31] Here documents - (2004-08-28)

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)
  [3630] Serialsing and unserialising data for storage and transfer in Perl - (2012-02-28)
  [3546] The difference between dot (a.k.a. full stop, period) and comma in Perl - (2011-12-09)
  [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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Handling binary data in Perl is easy!
Some other Articles
User defined sorting and other uses of callbacks in Tcl and Tk
Passing back multiple results in Tcl - upvar and uplevel
If its Sunday, must it be Weymouth?
Handling binary data in Perl is easy!
Single and double quotes strings in Perl - what is the difference?
A review of the Summer Sunday extra trains on the TransWilts line
When variables behave differently - Tie in Perl
Journey home by public transport for a Bank Holiday
Perl - a quick reminder and revision. Test yourself!
Not multidimentional arrays - but lists of lists. Much more flexible. Perl!
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