davido did an excellent job detailing the step-by-step creation of a general regex that would count your abc\d+ pattern within a line. However, I get the impression that you'd like a specific count of the number of occurrences for abc1 .. abc10 within a line.

davido indicated that your regex would only match abc followed by either a 1 or a 0, so it's not going to match all of abc10. Perhaps I'm over-simplifying the issue, but I'd likely use the following to count the number of times abc10 occurs within a line of text:

my @find = $line[$i] =~ /\babc10\b/g;
[download]

This regex will match your abc10 surrounded by a word boundary. Consider the following test for this regex:

use Modern::Perl;

my @patterns = map "abc$_", 1 .. 10;
my $str = join ' ', map { $_ = int( rand(10) ) + 1; "abc$_" } 1 .. 25;

say "String:\n$str\n\nContains:";

say "$_: " . @{ [ $str =~ /\b$_\b/g ] } for @patterns;
[download]

Output:

String:
abc9 abc6 abc2 abc7 abc3 abc10 abc2 abc10 abc1 abc3 abc2 abc1 abc4 abc
+4 abc2 abc4 abc8 abc10 abc10 abc7 abc3 abc10 abc6 abc1 abc8

Contains:
abc1: 3
abc2: 4
abc3: 3
abc4: 3
abc5: 0
abc6: 2
abc7: 2
abc8: 2
abc9: 1
abc10: 5
[download]

The script first generates a string of 25 random instances of the patterns (abc1 .. abc10) your interested in counting. It ends by looping through each pattern, using the regex (like the above) to provide a count of each occurrence of abc1 .. abc10 within that string.

Hope this helps!