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

by faq_monk (Initiate)
on Oct 08, 1999 at 00:20 UTC ( #600=perlfaq nodetype: print w/ replies, xml ) Need Help??

Current Perl documentation can be found at perldoc.perl.org.

Here is our local, out-dated (pre-5.6) version:

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 charcters 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";

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