Apache 2.4 never runs RewriteMap program

Since JavaScript cannot access HTTP header Accept-Language, I decided to pass this information to a custom cookie using .htaccess as follows:

RewriteRule .* - [CO=HTTP-Accept-Language:%{HTTP:Accept-Language}:%{HTTP_HOST}:1:/]

However, I quickly realized that cookies values are not allowed to use some "special" characters, including semicolon, which is used within Accept-Language header.

Therefore, I decided to use a simple RewriteMap program written in Perl to replace semicolons with underscore characters.

$| = 1;
while (<STDIN>) {
  print $_;

In my httpd.conf I defined the RewriteMap with

LogLevel trace8

<IfModule rewrite_module>
  RewriteEngine on
  Mutex default
  RewriteMap lc int:tolower
  RewriteMap uc int:toupper
  RewriteMap escape int:escape
  RewriteMap myprg "prg:/etc/httpd/rewrite/myprg.pl"

and to test these RewriteMap functions, I modified my .htaccess as follows:

RewriteEngine On
RewriteBase /

RewriteRule .* - [CO=Test1:${uc:%{HTTP:Accept-Language}}:%{HTTP_HOST}:1:/]
RewriteRule .* - [CO=Test2:${myprg:%{HTTP:Accept-Language}}:%{HTTP_HOST}:1:/]

Unfortunately, while uc RewriteMap function works fine, the external myprg doesn't.

With LogLevel trace8 in place, I expected some useful information in log file. But all I found about this external script was this:

map lookup OK: map=myprg key=en-US,en;q=0.9 -> val=

No error, just information that val is empty. Based on this finding, I modified my Perl script to include some internal logging:


use Cwd qw(abs_path);
use File::Spec;
use POSIX;

$| = 1;

my (undef, $directory, $filename) = File::Spec->splitpath(abs_path($0));

open my $file, '>>:encoding(UTF-8)', $directory . ($filename =~ s/(?:\.[^.]*)$/.log/r);
print  {$file} (strftime "%F %T", localtime time) . "\tRewriteMap script $filename started\n";
close   $file;

while (<STDIN>) {
  print $_;

After each change, I obviously also restarted Apache server by systemctl restart httpd

Then I realized that my Apache 2.4.6 (CentOS) never run the external RewriteMap script myprg.

I spent hours researching a possible problem on my side, but I didn't find anything wrong in my configuration files. What am I doing wrong? Why do I see no error, no warning, despite the script is never called?

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