m|\*\*(\w+)\b|g

##</code><code>##

while($text =~ m|\*\*(\w+)\b|g) {
    print "Found: " , $1 , "\n";
}

##</code><code>##

m|
 \*     #literal asterisk
 \*     #ditto
 (      #start capture
 \w+    #one or more word characters aka [A-Za-z0-9_]
 )      #end capture
 \b     #word boundary
|gx     #/x allows whitespace, /g makes it global (restart from last match position in this case)