That should work just fine. We're going to need more context to judge what's wrong. For example, this code works perfectly:

my $variable = "x";
my @line = split(/$variable/,"aaaxbbbxccc");
print @line;

$variable = "y";
@line = split(/$variable/,"aaaybbbyccc");
print @line;

$variable = "z";
@line = split(/$variable/,"aaazbbbzccc");
print @line;
[download]

It prints aaabbbccc each time.