my ( $week, $comptage, $index ) = qw{ W C I };
my $cmdc2= qq{mv M3.*txt ../../../dir_first_action_${week}/dir_M3_${we
+ek}_comptage_${comptage}_${index}};
print $cmdc2;
#Output:
#mv M3.*txt ../../../dir_first_action_W/dir_M3_W_comptage_C_I
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How does it "not work"?

Are you expecting the unix command mv to run? If so, you need to use qx{} or backticks, not qq{}. See Quote Like Operators in perlop.

Update: Forgot to mention backticks

Here is a suggestion, if not a specific answer. In the general case of system calls, system is generally preferable. as in:

my $command = qq{syscall $interp};
run_command_string($command);

sub run_command_string {
    my $command = shift;
    $log->info("attempt to run the following command:");
    $log->info("$command");
    system $command;

    if ( $? == -1 ) {
        $log->error("failed to execute: $!\n");
    }
    elsif ( $? & 127 ) {
        $log->error("child died with signal $? $!");
    }
    else {
        $log->info("child exited with value $?");
    }
}
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use File::Copy;
use File::Path;
#my $filename, $file2 declared somewhere

move( "$filename", "$file2" ) or die "move failed: $!";
#check File::Path's mkpath for use
[download]

As an observation, it would seem to make sense that since you can pick any delimiter for a qq "quote," if you are going to be using curly braces within the string, why not pick something other than curly braces as the delimiter? (It seems you aren't having to escape them, but for readability if nothing else)

Just a comment because I think being able to choose delimiters is a cool feature :)