Tried you suggestions, to no avail. Here's all the code, incase something else is causing the problem:

#!/usr/local/bin/perl
# this is the code for sever.pl, my mini-server

my @lines;

open(FILE1, $ARGV[0]);
while (<FILE1>) {
    push(@lines, $_);
}

($method, $url, $proto) = split(/ /, $lines[0]);

if ($method ne "GET") {
    if ($method ne "POST") {
        msg(400);
    }
}

if ($proto ne "HTTP/1.0") {
    msg(400);  #here's where sub msg doesn't work
}

if ($method eq "POST") {
    open(FILE2, $ARGV[1]);
    while (<FILE2>) {
        $ENV{'REQUEST_QUERYSTRING'} = $_;
    }
    print "the querystring is: $ENV{'REQUEST_QUERYSTRING'}\n";
    @q_string = split (/&/, $ENV{'REQUEST_QUERYSTRING'});
    foreach $pair (@q_string) {
        my @temp = split (/=/, $pair);
        $param{$temp[0]} = $temp[1];
        print "$temp[0] = $param{$temp[0]}\n";
    }
}

%msgs = ("200", "OK", "400", "Bad Request", "403", "Forbidden", "404",
+ "Not Found", "500", "Internal Server Error");

msg(400);   #here's where sub msg works
 
sub msg {
    $msg_num = @_[0];
    $msg_txt = "$msg_num $msgs{$msg_num}";
    print "HTTP/1.0 $msg_txt\n";
}
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and here's the file I'm passing to server.pl:

> more badreq.txt
GET /index.html HTTP/1.1
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and here's my output:

> ./server.pl badreq2.txt
HTTP/1.0 400 
HTTP/1.0 400 Bad Request
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What do you think? Thanks!