Personally, I would slurp the file into an array, and then create a new array for your expected output. then I would loop through the original array comparing the second and third element, and if $_1 gt $_2 then push what data you need to the final array like: 
for(@input){
    if($_[1] gt $_[2]){
    push (@output, "$_[0] $_[2] $_[1] $[3] +");
}

print "$_\n" for @output;

[download]
EDIT: Sorry for the confusion, you will need to split the element if you do it this way, please take this code into consideration: 
use strict;
use warnings;

my @input;
my @output;

while (<DATA>) {
    push @input, $_;
}
for (@input) {
    my @temp = split( /\s+/, $_ ); # you split on a delimiter, which i
+s 1 or more spaces in this case

    if ( $temp[1] gt $temp[2] ) {
        push( @output, "$temp[0] $temp[2] $temp[1] $temp[3] +" );
    }
    else {
        push @output, "$temp[0] $temp[1] $temp[2] $temp[3]";
    }
}

print "$_\n" for @output

__DATA__
red 15 2 smith
blue 4 10 walter

[download]
The reason I posted the code is because I earlier told you to do it a certain way, without also telling you that you would need to use the split function and create a temporary array to store the results from the split.

In reply to Re: switching two columns under conditions by james28909
in thread switching two columns under conditions by gghelpneeded

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.