Using Perl to extract the number of matches in a string

Question

How can I find out the number of disks in this string?

$str='disk 0_1 0_2 0_3';

In this $str, the number of disks is 3.

How can Perl output how many disks there are in this string?

Thank you!

score 3 · Answer 1 · answered Nov 27 '11 at 18:44

3

my $count = () = $str =~ /\d+_\d+/g;

answered Nov 27 '11 at 18:44

Zaid

+1, nice, I hardly understand why that works. Thought that the assignment to an empty list would reset/lose the count of elements in the original list. – Qtax Nov 27 '11 at 22:02
@Qtax : This is the [countof operator](http://github.com/cowens/perlopref); useful when you want to count how many items you have in your list but don't want to store it in an array. – Zaid Nov 28 '11 at 11:10
@Zaid Your link in the comment is dead. – FailedDev Nov 29 '11 at 14:40
@FailedDev : Looks like Chas needs to be notified – Zaid Nov 29 '11 at 14:44
1

@FailedDev : [Chas.](http://stackoverflow.com/users/78259/chas-owens) started the `perlopref` documentation project I tried to link to and he asked [a very interesting question](http://stackoverflow.com/questions/2897853/what-pseudo-operators-exist-in-perl-5) on SO a while ago :) – Zaid Nov 29 '11 at 19:53
@Zaid Oo :) Interestning indeed :) +1 for the lulz :) – FailedDev Nov 29 '11 at 19:54

score 1 · Answer 2 · edited Nov 27 '11 at 17:49

1

Try:

$disk_count = scalar( split ' ', $str) - 1;

edited Nov 27 '11 at 17:49

Martin York

answered Nov 27 '11 at 16:16

Nick

score 1 · Answer 3 · answered Nov 27 '11 at 16:17

1

my @result = $str=~ m/\d_\d/g;
print "Number of disks found : ", scalar(@result), "\n";

answered Nov 27 '11 at 16:17

FailedDev

this answer looks the most straight forward to understand, save the output to the array, then get array account. – brike Nov 28 '11 at 02:47
@brike : This solution is more or less the same as mine, except that I throw the array away. – Zaid Nov 29 '11 at 14:37

score 0 · Answer 4 · answered Nov 27 '11 at 16:15

0

my $counter = 0;
$counter++ while ($str =~ m/\d+_\d+/g);

answered Nov 27 '11 at 16:15

snoofkin

Can be done without looping as I remember, but I dont have perl in-front of me atm – snoofkin Nov 27 '11 at 16:15

4 Answers4