Either prepend the directory name when doing the file tests inside the loop:

my $dir = "/home/gaurav/Documents";
opendir my $dh, $dir or die "Couldn't open $dir: $!";

while (readdir $dh) {
    next if $_ eq "." or $_ eq ".." ;
    print $_, " " x (30 - length($_));
    
    my $file = "$dir/$_";
    
    # ...do file tests against $file here
}
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Or use chdir to change the working directory before entering the loop where you do the file tests:

my $dir = "/home/gaurav/Documents";
opendir my $dh, $dir or die "Couldn't open $dir: $!";

chdir($dir);

while (readdir $dh) {
    next if $_ eq "." or $_ eq ".." ;
    print $_, " " x (30 - length($_));
    
    # ...do file tests against $_ here
}
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