### start of bug.pl

@maindir = ('DIR1', 'DIR2', 'DIR3') ;

@suffix = ('s1', 's2', 's3') ; 

#################################################################################
### this works properly
#################################################################################

### for each directory in @maindir, descend into
for(@maindir) {
    $mn = $_ ;
    print STDERR $mn, "\n" ;
    chdir $mn ;

    opendir(THISDIR, ".") ;
    @allfiles = readdir(THISDIR) ;
    closedir(THISDIR) ;

    # for each of the files in this directory, check to see if it is
    # a valid subdirectory by testing for the existence of a file
    # named 'data.txt' in that subdirectory

    for(@allfiles) {
        $sd = $_ ;

        if ( -r $sd . "/data.txt" ) {

            # Found a valid subdirectory, now we want to open 3 different
            # files in that subdirectory, and store some data from those files
            # into a multidimensional hash

            print STDERR $sd, "\n" ;

            foreach(@suffix) {
                $sf = $_ ;

                print STDERR "$mn $sd $sf\n" ;

                # Build the filename of the data file we want
                $fn = "$sd/data." . $sf ;

                open(DATA, "<$fn") || print "Failed to open $fn\n" ;

                # Store the data in a multidimensional hash

                $v{$mn}{$sd}{$sf} = <DATA> ;

                close(DATA) ;
            }
        }
    }

    chdir ".." ;
}


#################################################################################
### Same as above, but now we use a while(<DATA>) loop at the inner-most level.
### Now it doesn't work, @suffix entries are set to "" after the first iteration.
#################################################################################

### for each directory in @maindir, descend into
for(@maindir) {
    $mn = $_ ;
    print STDERR $mn, "\n" ;
    chdir $mn ;

    opendir(THISDIR, ".") ;
    @allfiles = readdir(THISDIR) ;
    closedir(THISDIR) ;

    # for each of the files in this directory, check to see if it is
    # a valid subdirectory by testing for the existence of a file
    # named 'data.txt' in that subdirectory

    for(@allfiles) {
        $sd = $_ ;

        if ( -r $sd . "/data.txt" ) {

            # Found a valid subdirectory, now we want to open 3 different
            # files in that subdirectory, and store some data from those files
            # into a multidimensional hash

            print STDERR $sd, "\n" ;

            # uncomment the following to get the behavior expected
            #@suffix = ('s1', 's2', 's3') ; 

            foreach(@suffix) {
                $sf = $_ ;

                print STDERR "$mn $sd $sf\n" ;

                # Build the filename of the data file we want
                $fn = "$sd/data." . $sf ;

                open(DATA, "<$fn") || print "Failed to open $fn\n" ;

                # Store the data in a multidimensional hash (this will overwrite the hash, but that's
                # not the problem with this bug.

                while(<DATA>) {
                    $v{$mn}{$sd}{$sf} = $_ ;
                }

                close(DATA) ;
            }
            ## after falling out of the above loop, @suffix
            ## variables are now ("", "", "")
        }
    }

    chdir ".." ;
}