Also note that readdir returns the file names, but you have to prefix the path to them. Also, you only want to open files, not subdirectories, so I used grep to filter those out.

#!/usr/bin/perl
use warnings;
use strict;

my $path = '/Users/Maxi/Desktop/Verzeichnis beispiel';

opendir my $DIR, $path or die " the directory couldn't be opened\n";

my @folder = grep -f "$path/$_", readdir $DIR;

for my $file (@folder) {
    open my $FIL ,'<', "$path/$file" or die "the file $file couldn't b
+e opened: $!\n";
    while (<$FIL>) {
        print if /perl/i;
    }
}
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thanks a lot! i wrote this code in an attempt of reading and working with all the files in a directory but it doesnt work... yet if i specify the path of one file i get results im still a perl beginner so don´t laugh at my code ^^ thanks!

print "Enter a directory´s path to work with all files in a folder or 
+a single file path\n\n";
chomp(my $input =<STDIN>);

if ($input =~ /./){      ### attempt of recognizing a file extention
    $datei = $input;
    open(my $fastd,'<', $datei) or die "die datei $datei wurde nicht g
+eöffnet: $!\n";

    while (my $line = <$fastd>) {  #reading fasta file
        chomp $line;
        if ($line =~ /^>/) {
            $header = $line;
            $header =~ s/>//g;
            
        }
        else {
            $sequences->{$header} .= $line
        }
    }
    
}elsif($input =~ /[^.]/){  #### attempt of recognizing just a folder b
+ut i know it wont work always
    
    $path = $input;
    
    opendir my $DIR, $path or die " the directory couldn't be opened\n
+";
    
    my @folder = grep -f "$path/$_", readdir $DIR;

    for my $file (@folder){
        open (my $fastd ,'<', "$path/$file") or die "the file $file co
+uldn't be opened: $!\n";
        
        while (my $line = <$fastd>) {  #reading fasta file
            chomp $line;
            if ($line =~ /^>/) {
                $header = $line;
                $header =~ s/>//g;
                
            }
            else {
                $sequences->{$header} .= $line
            }
        }
    }
}
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What do you mean by "doesnt work"? Is there an error or warning, or does nothing happen, does the computer hang or burn in flames?

Dot has a special meaning in regular expressions. To match a literl dot, use /\./.

Also, you should use -d to test whether something is a directory - directory names with extensions are also valid.

لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

Your while loop is pretty useless.

while (@folder = readdir(DIR)){
    last;
}
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... is basically a convoluted way of writing:

@folder = readdir(DIR);
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Generally speaking, I'd recommend Path::Tiny as a much easier way of dealing with files and directories than Perl's built-ins.

use Path::Tiny 'path';

my $dir = path('/Users/Maxi/Desktop/Verzeichnis beispiel');

for my $file ($dir->children) {
   next if $file->is_dir;
   
   my $fh = $file->openr;
   while (my $line = <$fh>) {
      ...;
   }
}
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You failed to tell us what your problem is. Are we supposed to guess?

You don't need a while loop if you are reading the directory in list context:

You may also take a look at the glob function, which is often more practical than opendir/readdir.

use File::Find::Rule qw/ find /;
my @spielfiles = find( file => maxdepth => 1, in => $spielpath );

Modern Perl a loose description of how experienced and effective Perl 5 programmers work....You can learn this too., Chapter 9. Managing Real Programs, Directories and Paths, Manipulating Paths

Hello,

You can get the same functionality using glob operator(as LaurentR has said) and with fewer lines of code.

Here you go!

#!/usr/bin/perl

my @files = glob( "$ARGV[0]/*.*" );

for my $file (@files) {
    
open NB_FILE, '<', $file or die "Couldn't open Netbackup file!";
while(<NB_FILE>)
{
print "Printing line $. from file $file\n";
print $_;
}
close NB_FILE or die "Couldn't close the file properly!"  
}
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print "Enter a directory´s path to work with all files in a folder or 
+a single file path\n\n";
chomp(my $input = <STDIN>);

if ($input =~ /./){      ### attempt of recognizing a file extention

... process file

}elsif ($input =~ /[^.]/){  #### attempt of recognizing just a folder 
+but i know it wont work always

... process folder

}
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print "Enter a directory´s path to work with all files in a folder or 
+a single file path\n\n";
chomp(my $input = <STDIN>);

if (-f $input){      # $input is the name of an existing file

... process file

}elsif (-d $input){  # $input is the name of an existing folder

... process folder

}
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