pepijn,
I believe the following will do:

my @results = $string =~ /(cde)/g;

# Also check out perldoc -f quotemeta if cde is actually a $var
[download]

Cheers - L~R

Update: I almost forgot my manners. Welcome to the Monastery. The site and community is quite large and may seem a bit overwhelming. If so, be sure to check out the PerlMonks FAQ.