Perl: renaming doesn't work for $value filename [closed] - perl

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I want to fill the folder with copies of the same file that would be called differently. I created a filelist.txt to get filenames using Windows cmd and then the following code:
use strict; # safety net
use warnings; # safety net
use File::NCopy qw(copy);
open FILE, 'C:\blabla\filelist.txt';
my #filelist = <FILE>;
my $filelistnumber = #filelist + 1;
my $file = 0;
## my $filename = 'null.txt';
my $filename = $filelist[$file];
while( $file < $filelistnumber ){
copy('base.smp','temp.smp');
rename 'temp.smp', $filename;
$file = $file + 1;
};
If I try renaming it into 'test.smp' or whatever, it works. If I try the code above, I get this:
Use of uninitialized value $filename in print at blablabla/bla/bla.pl line 25, <FILE> line 90.
What am I doing wrong? I feel there's some kind of little mistake, a syntax mistake probably, that keeps evading me.

Answer 1

First, here's some improved code:
use strict;
use warnings;
use File::Copy;
while (<>) {
chomp;
copy('base.smp', $_) or die $!;
}
You'll save it as script.pl and invoke it like this:
$ perl script.pl C:\blabla\filelist.txt
In what ways is this code an improvement?
It uses the core module File::Copy instead of the deprecated File::NCopy.
It uses the null filehandle or "diamond operator" (<>) to implicitly iterate over a file given as a command line parameter, which is simple and elegant.
It handles errors in the event that copy() fails for some reason.
It doesn't use a while loop or a C-style for loop to iterate over an array, which are both prone to off-by-one errors and forgetting to re-assign the iterator, as you've discovered.
It doesn't use the old 2-argument syntax for open(). (Well, not explicitly, but that's kind of beyond the scope of this answer.)
What am I doing wrong? I feel there's some kind of little mistake, a
syntax mistake probably, that keeps evading me.
A syntax error would have resulted in an error message saying that there was a syntax error. But since you asked what you're doing wrong, let's walk through it:
use File::NCopy qw(copy);
This module was last updated in 2007 and is marked as deprecated. Don't use it.
open FILE, 'C:\blabla\filelist.txt';
You should use the three-argument form of open, use a lexical filehandle, and always check the return values of system calls.
my #filelist = <FILE>;
Rarely do you need to slurp an entire file into memory. In this case, you don't.
my $filelistnumber = #filelist + 1;
There's nothing inherently wrong with this line, but there is when you consider how you're using it later on. Remember that arrays are 0-indexed, so you've just set yourself up for an out of bounds array index. But we'll get to that in a second.
my $filename = $filelist[$file];
You would typically want to do this assignment inside your loop, lest you forget to update it after incrementing your counter (which is exactly what happened here).
while( $file < $filelistnumber ){
This is an odd way to iterate over an array in Perl. You could use a typical C-style for loop, but the most Perlish thing to do would be to use a foreach-style loop:
for my $element (#array) {
...
}
Each element of the list is localized to the loop, and you don't have to worry about counters, conditions, or array bounds.
copy('base.smp','temp.smp');
Again, always check the return values of system calls.
rename 'temp.smp', $filename;
No need to do a copy and a rename. You can copy to your final destination filename the first time. But if you are going to rename, always check the return values of system calls.
};
Blocks don't need to be terminated with a semicolon like simple statements do.

Answer 2

You should avoid using bareword file handles. When opening you should open using a file reference like and make sure you catch it if it fails:
open(my $fh, '<', 'C:\blabla\filelist.txt') or die "Cannot open filelist.txt: $!";
The $fh variable will contain your file reference.
For your problem it looks as though your filelist.txt must be empty. Try using Data::Dumper to print out your #filelist to determine it's contents.
use Data::Dumper;
EDIT:
Looks like you are also wanting to be setting the $filename variable to the next one in the list for each iteration, so put $filename = $filelist[$file]; at the beginning of your loop.
Your problem could be that you are looping too far? Try getting rid of the + 1 in my $filelistnumber = #filelist + 1;