#!/usr/bin/env perl -l

use strict;
use warnings;

my @lines = (
    'Iteration {Applied Field} {Total Energy} Mx',
    '{blaa blaa blaa}',
    'Iteration {Applied Field}  {Total Energy}    Mx',
    'Iteration {Applied Field} A  {Total Energy}    Mx  F G {Third test line}',
    'Iteration {Applied Field}  {Total Energy}    Mx Fx {a} B C D {E F} G',
    'Iteration {Applied Field}  {Total Energy}  {Foo}  {  a b   c d  }  Mx',
);

my $re_hard_to_read = qr/(?>[{]([^}]+)|\s*(?![{}])(\S+))/;

my $re_easy_to_read = qr/(?> 
    [{] ( [^}]+ )
    |
    \s* (?! [{}] ) ( \S+ )
)/x;

my $re_fully_annotated = qr/
    (?>             # start non-capturing, non-backtracking, alternation
        [{]         # MATCH: exactly one literal left brace
        (           # start capture
            [^}]+   # CAPTURE: one or more of any character except right brace
        )           # end capture
    |               #   - OR -
        \s*         # MATCH: zero or more whitespace
        (?!         # start zero-width negative lookahead assertion
            [{}]    # ASSERT: next character is not left or right brace
        )           # end zero-width negative lookahead assertion
        (           # start capture
            \S+     # CAPTURE: one or more non-whitespace characters
        )           # end capture
    )               # end non-capturing, non-backtracking, alternation
/x;

#my $re = $re_hard_to_read;
#my $re = $re_easy_to_read;
my $re = $re_fully_annotated;

for (@lines) {
    # Print output heading
    print join "\n$_\n" => ('-' x 60) x 2;

    # Array to hold header names
    my @header_names;

    # Capture header names
    push @header_names => $+ while /$re/g;

    # Output header names
    print join "\n" => @header_names;
}

##</code><code>##

------------------------------------------------------------
Iteration {Applied Field} {Total Energy} Mx
------------------------------------------------------------
Iteration
Applied Field
Total Energy
Mx
------------------------------------------------------------
{blaa blaa blaa}
------------------------------------------------------------
blaa blaa blaa

##</code><code>##

------------------------------------------------------------
Iteration {Applied Field}  {Total Energy}    Mx
------------------------------------------------------------
Iteration
Applied Field
Total Energy
Mx
------------------------------------------------------------
Iteration {Applied Field} A  {Total Energy}    Mx  F G {Third test line}
------------------------------------------------------------
Iteration
Applied Field
A
Total Energy
Mx
F
G
Third test line
------------------------------------------------------------
Iteration {Applied Field}  {Total Energy}    Mx Fx {a} B C D {E F} G
------------------------------------------------------------
Iteration
Applied Field
Total Energy
Mx
Fx
a
B
C
D
E F
G
------------------------------------------------------------
Iteration {Applied Field}  {Total Energy}  {Foo}  {  a b   c d  }  Mx
------------------------------------------------------------
Iteration
Applied Field
Total Energy
Foo
  a b   c d  
Mx