I personally believe that I will also comment on your code. I've given a glance at the other responses thus far, but I'm replying as if I only saw your post: you'll surely notice some repetitions with comments by others, this should help to stress some issues it has, and in particular to show you why it was a bad idea to post it in this section to start with.

#!usr/bin/perl

use strict;
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"Wrong" shebang line (but it won't matter if you're under Windows - not a good reason not to put it right there too: it will help portability!) And missing use warnings; line too.

# This is a program which reads in a list of file names from the comma
+nd 
# line and prints which files are readable, writable and/or executable
+,
# and whether each file exists.
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Not terribly compelling, but for a snippet you may have considered using a tiny piece of POD rather than comments.

 while ($i < scalar(@ARGV)) {
    open(MYFILE, $ARGV[$i]) or die("Error: cannot open file '$ARGV[$i]
+'\n");
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Three issues:

• in [Pp]erl, TMTOWTDI, but there are indeed prefer{red,able} WTDI for some specific and common tasks: please let me tell you that the way you adopt to iterate over @ARGV is the most uselessly byzantine I could think of. Incidentally, Perl DWIM most of the times to help you write clean and terse code: that scalar is redundant there;
• if you're using the two-args form of open you may well rely on *ARGV's implicit open() instead. But then you use file tests in which case I would avoid opening at all unless you have a good reason to so. However, if you do then all of the remaining "standard" recommendations about open() apply too: in particular those about using the three-args form, and lexical handles. I'm not repeting here why it's good to follow them because it is done ad nauseam on a daily basis;
• it would also be good to say people why something went wrong, and thus include $! in the error message.

     print "$ARGV[$i] is readable!\n" if -r MYFILE;
    print "$ARGV[$i] is writable!\n" if -w MYFILE;
    print "$ARGV[$i] is executable!\n" if -x MYFILE;
    print "$ARGV[$i] exists!\n" if -e MYFILE;
    $i++;
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In terms of logic and UI: are you sure about that order? Incidentally, if the file didn't exist, could have you opened for reading?

 } # end while
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If you really needed that, then probably you wanted a language which supports such specifications at the level of the syntax. Or else you'd have a too big a while loop, in which case I'd recommend you to trim it down. All in all I would rewrite your program like

#!/usr/bin/perl

use strict;
use warnings;
use 5.010;

for my $file (@ARGV) {
    -e $file or next;
    say "`$file' exists!";
    say "`$file' is ", ( $_->[1]() ? "" : "not " ), $_->[0]
    for [readable   => sub () { -r _ }],
        [writable   => sub () { -w _ }],
        [executable => sub () { -x _ }];
}

__END__
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