Question

Possible Duplicate:
Why does Perl's glob return undef for every other call?

This is a continuation of another problem I was having where I needed to find a file that had a long name but I knew what part of the name was, here is the code I used:

my @RTlayerRabcd = ("WIRA_Rabcd_RT","WIRB_Rabcd_RT","WIRC_Rabcd_RT","WIRD_Rabcd_RT","WIRE_Rabcd_RT","BASE_Rabcd_RT");

#Rabcd calculations
for($i = 0; $i < 6; $i++) 
{
    print "@RTlayerRabcd[$i]\n";
    #Searching for Rabcd Room Temperature readings
    my $file = glob($dir . "*@RTlayerRabcd[$i]" . '.txt');
    print "$file\n";
    my $Rtot = 0;
    #Open file, Read line
    open (FILE, $file);
    while (<FILE>)
    {
        #read line and and seperate at "tab" into $temp, $Res 
        chomp;
         ($Res, $temp) = split("\t");   
        $j++;
        $Rtot=$Res+$Rtot;

     }
     close (FILE);

    $Ravg = $Rtot/$j;
    print FILE_OUT "$Ravg \t";



 }

After I run the code I get the following print outs:

WIRA_Rabcd_RT                                                               
Vesuvious_C6R8_051211/vesu_R6C8_05112011_WIRA_Rabcd_Rt.txt
WIRB_Rabcd_RT

WIRC_Rabcd_RT                                                      
Vesuvious_C6R8_051211/vesu_R6C8_05112011_WIRC_Rabcd_Rt.txt                            
WIRD_Rabcd_RT                                                

WIRE_Rabcd_RT                                                   

BASE_Rabcd_RT                                             
Vesuvious_C6R8_051211/vesu_R6C8_05112011_BASE_Rabcd_Rt.txt

The program seems to be skipping files, any idea why?

Answer 1

In scalar context, glob iterates through all files matched by the glob, returning undef after the last one. It’s intended to be used as the condition in a while loop, for example:

while (my $file = glob('*.c')) {
  say $file;
}

The iterator is tied to that particular call to glob. Once the iteration has started, there’s no way to reset the iterator early. glob ignores its argument until after it has returned undef.

You can fix your problem by using glob in list context:

my ($file) = glob($dir . "*@RTlayerRabcd[$i]" . '.txt');