#!/usr/bin/env perl

use strict;
use warnings;
use Carp;
use English;

# Do some work
foreach my $file ( glob('/root/fd/fg/*.txt') ) {
    next if(-f $file . '.done'); # Skip if '*.done' file exists

    open(my $ifh, '<', $file) or croak($ERRNO);

    my $ad;
    my @rt;

    while((my $line = <$ifh>)) {
        if($line =~ m/ad/) {
            ($line =~ tr/a-z,=//d ) ;
            $ad = $line ;

        }
        if ($line =~ m/rt /){
            ($line =~ tr/a-z,=//d) ;
            push (@rt , $line);
        }
    }

    close $ifh; # Need to close fille after working on it.

    open(my $ofh, '>', $file . '.done') or croak($ERRNO); # Create '*.done' file
    close($ofh);
}

# Cleanup
foreach my $file ( glob('/root/fd/fg/*.txt.done') ) {
    my $realfname = $file;
    $realfname =~ s/\.done$//;

    if(!-f $realfname) {
        unlink $file;
    }
}

##</code><code>##

#!/usr/bin/env perl

use strict;
use warnings;
use Carp;
use English;
use File::Copy;

# Do some work
foreach my $file ( glob('/root/fd/fg/*.txt') ) {

    open(my $ifh, '<', $file) or croak($ERRNO);

    my $ad;
    my @rt;

    while((my $line = <$ifh>)) {
        if($line =~ m/ad/) {
            ($line =~ tr/a-z,=//d ) ;
            $ad = $line ;

        }
        if ($line =~ m/rt /){
            ($line =~ tr/a-z,=//d) ;
            push (@rt , $line);
        }
    }

    close $ifh; # Need to close fille after working on it.

    # Rename/move file
    move($file, $file . '.done');
}

##</code><code>##

...
# Do some work
my @files = glob('/root/fd/fg/*.txt');
sleep(4);
foreach my $file(@files) {
...