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 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)
[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)
[2801] Binary data handling with unpack in Perl - (2010-06-10)
[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)
Some other Articles
Melksham Art CafePerl - functions for directory handlingObject Relation Mapping (ORM)Asda opening large new store in MelkshamPerl, the substitute operator sBathtubs and pecking birdsfor loop - how it works (Perl, PHP, Java, C, etc)Judging the quality of contributed Perl codeSunday afternoonWhat are factory and singleton classes?