$foo = '^';
m/$foo/

##</code><code>##

my $str = "acb^def^123^456";
my $foo = '^'; 
$foo =~ s/([\\\|\(\)\[\{\^\$\*\+\?\.])/\\$1/;
my @fields = split /$foo/, $str;
my $out = join '|', @fields;
print "$out\n";

##</code><code>##

my $str = "acb\tdef\t123\t456";
my $foo = "\t";

##</code><code>##

"first,field","second,""field"with','junk","third'field