Part of what makes Perl such a useful language is its powerful string-matching
and handling capabilities. Regular expressions are basically patterns a
programmer can compare a string of text to. Matching a regular expression with
a string of text either returns true or false. The two main pattern matching
operators are
m// and
s//. These are the matching and
substitution operators respectively. Another function that makes use of regular
expressions is
split
The matching operator
m// is normally written //.
Perl allows you to change the delimiters to something besides /. If you don't
change the delimiters from /, you can use // instead of m//.
Now for a quick example of m//:
while(<>){
if(/the/){ #does $_ contain the
print "Your line of text contains the word 'the'\n";
}
}
Now for a quick example of
s///:
@machines_os=("OpenBSD","Windows","Linux", "Windows");
foreach(@machines_os){
s/Windows/Linux/;
}
This function goes through each of the items in @machine_os. If any of
them contain Windows, the thing between the first set of //. It is replaced with
Linux the string between the second and third /'s. You can see why you've gotta love Perl. Instead of
1 OpenBSD machine, 2 Windows machines and a Linux box, I now have 1 OpenBSD box
and 3 Linux machines. At least that is what @machines_os now contains.
Now on to
Quantifiers in regular expressions.