Perl, the substitute operator s

In Perl, the s (or substitute) operator allows you to match a regular expression and replace the part of your incoming string that matched with another string. Your incoming string should be specified to the left of an =~ operator and is changed in situ. For example:

$sample = "The cat sat on the mat";

$sample =~ s/.at/dog/;

Would replace cat (as "." means any character) with dog. It would stop at that point, as the s operator only changes a single occurence unless a g for global modifier is added on the end. So

$sample = "The cat sat on the mat";

$sample =~ s/.at/dog/g;

Would give you The dog dog on the dog

• if you don't specify the variable that s is to work on, it works on the contents of $_

• if you add an e modifier, it performs the output string as a perl expression and substitues in the result.

• if you specify $1 or \1 in the output string, you'll mean the first captured part of the incoming string that matched, and so on.

• if you use the value returned by the substitute operator, you'll find that it contains the number of changes made.

There's an example of all of these features just added to our web site here
(written 2007-06-08)

Associated topics are indexed under

P212 - Perl - More on Character Strings
  [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)
  [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)
  [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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Some other Articles

Melksham Art Cafe
Perl - functions for directory handling
Object Relation Mapping (ORM)
Asda opening large new store in Melksham
Perl, the substitute operator s
Bathtubs and pecking birds
for loop - how it works (Perl, PHP, Java, C, etc)
Judging the quality of contributed Perl code
Sunday afternoon
What are factory and singleton classes?

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