Using chomp in a while condition is usually not what you want. It'd skip the last line of a file if it didn't end in a newline.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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   last if $line=~/^$/;
   # or using length..
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UPDATE: you can also use last unless $line; to quit the loop, but this breaks if 0 is passed. If 0 is valid you can last unless defined $line; see below Laurent_R.

Additionally if move the chomp inside the loop you can use CTRL-Z to end fidding STDIN

Notice that chomp returns the number of removed chars, not the chomped string (added in the same time of the below answer..). Considering this and avoiding extra variable $line you can have anything in the while condition:

while ( chomp ( $_ = <STDIN>) and length $_){
    print "  [$_]\n";
}
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L*

you can also use last unless $line; to quit the loop, but this breaks if 0 is passed. If 0 is valid you can last unless defined $line;

The last unless defined $line; statement will not work either, because even if $line is empty, it will still be defined.

Your original solution, i.e. last if $line=~/^$/; (or length $line ...), is definitely better.

In general I'd recommend avoiding the pattern while(chomp(<$handle>)) because it often suffers from issues (another explanation).

You might also want to consider using a module for prompting.

use IO::Prompt 'prompt';
my $resp = prompt("Foo? ", -yn);

use Term::ReadLine;
my $term = Term::ReadLine->new;
my $line = $term->readline("Bar? ");
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Or even this (the advantage being ExtUtils::MakeMaker is a core module, even though it has a completely different purpose):

use ExtUtils::MakeMaker 'prompt';
my $value = prompt("Quz?","n");
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The module does have another advantage: "If prompt() detects that it is not running interactively and there is nothing on STDIN or if the PERL_MM_USE_DEFAULT environment variable is set to true, the $default will be used without prompting. This prevents automated processes from blocking on user input."

Update 2020-11-30: See also the more powerful IO::Prompter, simple example here.

For terminal user input, I recommend following normal unix conventions: any white space in front does not matter and any white space after the input does not matter. You do not need chomp() when using s/\s*$//; because all line endings are considered white space.

I strongly prefer to put the condition that "ends the loop" in the loop conditional instead of burying it somewhere within the loop's body. With the "comma operator", the only part of the statement that matters for "truthfulness" is the last clause. If there are say 9 things that can end the loop, I would try to put the very most common of those in the conditional and leave the other 8 to be within the loop (e.g. last if XYZ;).

For terminal input like this, consider the following 2 examples:

First, simple Blank Line to exit:

#!/usr/bin/perl
use strict;
use warnings;

my $line;  # don't put a my declaration in a loop conditional

print "Enter data at prompt, blank line to finish data entry\n";

while ( (print "> "), $line = <STDIN>, $line !~ /^\s*$/)
{
   $line =~ s/^\s*//;     # delete leading spaces
   $line =~ s/\s*$//;     # delete trailing spaces
                          # no chomp is needed because both
                          # carriage return and line feed are
                          # white space characters (\s) in Perl
                          # regex lingo
   
   print "Data processed:$line\n";
}

print "LOOP EXITED DUE TO BLANK LINE\n";
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#!/usr/bin/perl
use strict;
use warnings;

my $line;  # don't put a my declaration in a loop conditional

print "Enter data at prompt or type: quit to stop data entry\n";

while ( (print "> "), $line = <STDIN>, $line !~ /^\s*Q(uit)$/i)
{
   $line =~ s/^\s*//;     # delete leading spaces
   $line =~ s/\s*$//;     # delete trailing spaces
                          # no chomp is needed because both
                          # carriage return and line feed are
                          # white space characters (\s) in Perl
                          # regex lingo
   
   print "Data processed:$line\n";
}

print "LOOP EXITED DUE TO QUIT \n";
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...
while ( not eof( STDIN ) )
{
    chomp( my $line = <> );
    ...
}
...
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Update: Ignore this, I misread the question :-}