You code is working already.

use strict;
use warnings;
use Data::Dumper;

my @mydata = qw/ abcd cabc abcdabcd defg xyz /;

for(@mydata)
{
    if($_ =~ /abc/g)
    {
        print "$_\n";  #print the line
    }
}
[download]

And the output -

abcd
cabc
abcdabcd
[download]

I have a feeling that you want to do this with a one-liner instead? Which is already answered by BrowserUk.