if ($file =~ /-\(lala\)-/) { ...
[download]

will work, but

my $skip = "/-\(lala\)-/";
if ($file =~ /$skip/)
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won't work. The reason is the difference where the backslash is used. In the first case it is used in a regexp, where it protects the (), while in the second one, it is used in a string where it is interpreted as a simple () used in the regexp again as capturing characters. You can use one of the following workarounds:

my $skip = "/-\\(lala\\)-/";  # protect the backslash for itself
if ($file =~ /$skip/) { ...
[download]

my $skip = '/-\(lala\)-/';  # use singe quotes
if ($file =~ /$skip/) { ...
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my $skip = "/-(lala\-/";  
if ($file =~ /\Q$skip/) { ... # quote it in the regexp
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my $skip = qr/-\(lala\)-/;    # use precompiled regexps
if ($file =~ /$skip/) { ...
[download]

Greetings,
Janek