Velocity Reviews - Computer Hardware Reviews

Velocity Reviews > Newsgroups > Programming > Perl > Perl Misc > FAQ 4.29 How can I count the number of occurrences of a substring within a string?

Reply
Thread Tools

FAQ 4.29 How can I count the number of occurrences of a substring within a string?

 
 
PerlFAQ Server
Guest
Posts: n/a
 
      01-04-2011
This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

--------------------------------------------------------------------

4.29: How can I count the number of occurrences of a substring within a string?

There are a number of ways, with varying efficiency. If you want a count
of a certain single character (X) within a string, you can use the
"tr///" function like so:

$string = "ThisXlineXhasXsomeXx'sXinXit";
$count = ($string =~ tr/X//);
print "There are $count X characters in the string";

This is fine if you are just looking for a single character. However, if
you are trying to count multiple character substrings within a larger
string, "tr///" won't work. What you can do is wrap a while() loop
around a global pattern match. For example, let's count negative
integers:

$string = "-9 55 48 -2 23 -76 4 14 -44";
while ($string =~ /-\d+/g) { $count++ }
print "There are $count negative numbers in the string";

Another version uses a global match in list context, then assigns the
result to a scalar, producing a count of the number of matches.

$count = () = $string =~ /-\d+/g;



--------------------------------------------------------------------

The perlfaq-workers, a group of volunteers, maintain the perlfaq. They
are not necessarily experts in every domain where Perl might show up,
so please include as much information as possible and relevant in any
corrections. The perlfaq-workers also don't have access to every
operating system or platform, so please include relevant details for
corrections to examples that do not work on particular platforms.
Working code is greatly appreciated.

If you'd like to help maintain the perlfaq, see the details in
perlfaq.pod.
 
Reply With Quote
 
 
 
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Re: How include a large array? Edward A. Falk C Programming 1 04-04-2013 08:07 PM
FAQ 4.29 How can I count the number of occurrences of a substring within a string? PerlFAQ Server Perl Misc 0 04-22-2011 10:00 PM
Beginners: Count occurrences of a string within a string yogi_bear_79 C++ 9 02-28-2008 09:14 PM
count the number of occurrences of a substring in a string sibingpeter@gmail.com C Programming 4 10-02-2005 07:37 PM
counting number of occurrences of every possible substring in multiple files C3 Perl Misc 3 09-29-2004 04:53 PM



Advertisments