#!/usr/bin/perl -w
use strict;

while ( (print "Enter some text: "), 
        (my $line=<STDIN>) !~ /^\s*q(uit)?\s*$/i  
      )
{
   next if $line =~ /^\s*$/; #blank line just re-prompts
   chomp ($line);    # a real app would probably do this
   print "$line\n";  # although here I just add it back
}
print "program exited\n";

__END__
C:\TEMP>stdcmdline.pl
Enter some text: 25436
25436
Enter some text: QuIT
progam exited

C:\TEMP>stdcmdline.pl
Enter some text: quI
quI
Enter some text: Q
progam exited

C:\TEMP>stdcmdline.pl
Enter some text: asdf
asdf
Enter some text: qu
qu
Enter some text: QuIT
program exited

C:\TEMP>stdcmdline.pl
Enter some text: quited
quited
Enter some text: 3245
3245
Enter some text: Q
program exited

C:\TEMP>stdcmdline.pl
Enter some text: q
program exited

C:\TEMP>stdcmdline.pl
Enter some text:        quit
program exited