Do you have to use regexp? In the past, I've solved this issue by splitting string on "escapes", and then walking all parts merging 2 subsequent "escapes" into character and placing them back into text.

Something like this

my @parts = split /([\\@])/, $input;
my $txt = shift @parts;
while(@parts > 1)
{
    shift @parts;
    my $t = shift @parts;
    if($t eq '')
    {
        # get the escaped "escape"
        $txt .= shift @parts;
        # get the text that follows it
        $txt .= shift @parts;
        next;
    }
    $t =~ s/^(\w+)//;
    my $cmd = $1;
    $txt .= "::$cmd\::$t";
}

$txt .= shift @parts if @parts;
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