I prefer not to use while(1) type loops for anything other than say in a server loop. For a command loop I prefer to put the prompt and the exit condition test right there in the loop conditional. You can modify the regex for "quit" or whatever. Here the loop exits on a blank line - is that what you wanted?

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

my $cmd;
while ((print "enter cmd: "), $cmd=<STDIN> and $cmd !~/^\s*$/)
{
    chomp $cmd;
    print "cmd was: $cmd\n";
}
print "loop exited\n";
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Update: Perhaps you wanted to loop until the first non-blank line was entered?

my $cmd="";
until ($cmd !~ /^\s*$/){print "enter cmd: "; $cmd=<STDIN>;}

chomp $cmd;
print "cmd was: $cmd\n";
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I guess I'm not so clear about exactly you want to do.

Basically, I try to construct these loops such that the "last;" statement if any, is not the main, "normal" way that the loop exits. I use that to mean, "oh, we are quitting abnormally early" for some reason - maybe finding the first match or something like that.

If you are wondering why I used a regex, normally leading/trailing blanks on user input are ignored and I would have some statement to trim these instead of just a simple chomp; Anyway 3 spaces and one tab should be counted as just a "whitespace" line.