#!/usr/bin/perl

$icase = 'i';
$str = 'ASdf';

if ( 'asdf' =~ /$str/$icase ) { print "it works!\n" }

##</code><code>##

$ perl test.pl
Scalar found where operator expected at test.pl line 6, near "/$str/$icase"
        (Missing operator before $icase?)
syntax error at test.pl line 6, near "/$str/$icase "
Execution of test.pl aborted due to compilation errors.