How to loop through a directory in perl - perl

Question

I have a directory dir1 containing several hundreds of files, which are to be iteratively processed by a speech program called HRest. The program is supposed to take each file one by one, process it and put it in a new directory (as dir2 for first iteration) to be used in next iteration. My problem is that i don't know if the way I've employed to loop through the files in dir1, and also the way I am running the script (trainhmms.pl dir1 1) is correct.
If the files in dir1 are L1, L2, L3, ..., L500, I want HRest to be executed as
HRest -T 1 -I timedlabels_train.mlf -t -i 20 -l dir1/L1 -M dir2 -S train.scp
for the first file, and as
HRest -T 1 -I timedlabels_train.mlf -t -i 20 -l dir1/L2 -M dir2 -S train.scp
for the next file, and so on for all files. Then in next call of the script, I want it to be changed to
HRest -T 1 -I timedlabels_train.mlf -t -i 20 -l dir2/L1 -M dir3 -S train.scp
for the first file, and so on..
Here is the script for the first iteration:
#!/usr/bin/perl
use File::Slurp;
# Usage: trainhmms.pl dir1 1
# dir1: Folder containing models after being initialised by HInit (L1,L2,..,L512)
$file = $ARGV[0];
$iter = $ARGV[1];
my #files = read_dir '/Users/negarolfati/Documents/Detection_rerun/AF_TIMIT/1_state//trainHMMs/dir1';
for my $file ( #files ) {
$iter2 = $iter+1;
$cmd = "HRest -T 1 -I timedlabels_train.mlf -t -i 20 -l '$dir[$iter]/$file' -M '$dir[$iter2]' -S train.scp ";
system("$cmd");
}

Answer 1

You can't just use readdir on a directory string. You have to opendir the string, then readdir from the directory handle that you get, and finally closedir the handle.
You must also remember that readdir returns directory names as well as file names, and the pseudo-directories . and .. too. To filter out just the files, you can use the -f test operator. And it is usually most convenient to chdir to the directory you are reading so that you don't have to append the path to each file name that readdir returns before you do the test.
I don't know what HRest is, but if your command line must be executed from a specific working directory (perhaps to acccess timedlabels_train.mlf and train.scp) then please say so. I will have to remove the chdir statement.
Something like this should get you going. I have used autodie, which does automatic checks on file system operations. It saves having to check chdir and opendir explicitly each time with or die $!.
#!/usr/bin/perl
use strict;
use warnings;
use autodie;
use File::Spec::Functions 'catdir';
my ($file, $iter) = #ARGV;
my $root = '/Users/negarolfati/Documents/Detection_rerun/AF_TIMIT/1_state/trainHMMs';
my $dir1 = catdir $root, 'dir'.$iter;
my $dir2 = catdir $root, 'dir'.($iter+1);
chdir $dir1;
opendir my ($dh), '.';
my #files = grep -f, readdir $dh;
closedir $dh;
for my $file ( #files ) {
my $cmd = "HRest -T 1 -I timedlabels_train.mlf -t -i 20 -l '$dir1/$file' -M '$dir2' -S train.scp";
system($cmd);
}
Update
Here is an alternative version that avoids chdir so that the current working directory remains unchanged.
I have added the secondary loop that was in your bash script. I have also added a print statement so that you can see each command before it is executed.
To allow the system call to go ahead, just delete or comment out the next statement.
#!/usr/bin/perl
use strict;
use warnings;
use autodie;
use File::Spec::Functions qw/ catdir catfile /;
STDOUT->autoflush;
my $root = '/Users/negarolfati/Documents/Detection_rerun/AF_TIMIT/1_state/trainHMMs';
for my $iter (1 .. 4) {
my $dir1 = catdir $root, 'dir'.$iter;
my $dir2 = catdir $root, 'dir'.($iter+1);
opendir my ($dh), $dir1;
while (my $node = readdir $dh) {
my $file = catfile($dir1, $node);
next unless -f $file;
my $cmd = "HRest -T 1 -I timedlabels_train.mlf -t -i 20 -l '$file' -M '$dir2' -S train.scp";
print $cmd, "\n";
next; # Remove for full functionality
system($cmd);
}
closedir $dh;
}

Answer 2

You can do this:
my #files = <$path/*>;
foreach my $filename ( reverse(#files) ) {
...
}