如何比较Perl中的字符串?

今天第一次练习Perl。我想循环,直到用户键入“退出”。输入“退出”不会停止,这是一个无限循环。我使用字符串比较错误吗?我原来有这个:

do 
{
    print "Enter a sentence or phrase to convert or 'quit': ";
    $choice = <STDIN>;  # user input variable
} while ($choice ne "quit");

$quit = "quit";

do 
{
    print "Enter a sentence or phrase to convert to or 'quit': ";
    $choice = <STDIN>;  # init user input variable
    $dif = $quit ne $choice;
} while ($dif == 1);