Your code can be optimized a lot. Here is some proposal but I cannot test it as I do not have your directories at hand. I added comments to explain what I am doing so I hope it helps: 

my @infiles = &GetINDirFiles($inpath);  
# instead of having an array with the outfiles use a hash for faster l
+ookup
# also remove suffix at this stage already, no need to do it again and
+ again in the loop
# you need to escape your suffix variable in \Q...\E for special chara
+cters such as the dot
# only remove the suffix at the end, no need for (.*)
my %outfiles = map { s/\Q$outsuffix\E$//; $_ => 1 } &GetOUTDirFiles($o
+utpath);

my $index = 0; # index used to get string position in array
foreach my $infile (@infiles) {
        # see above re the replacement
        $infile =~ s/\Q$insuffix\E$//;      # remove suffix to do comp
+aration # Added by me
        # instead of loop through array of outfiles do hash lookup
        push (@delindex, $index) if exists $outfiles{$infile};
        $index += 1;
}

[download]

UPDATE: Forget my code above. You can write this as:

my %outfiles = map { /(.*)\Q$outsuffix\E$/; $1 => 1 } &GetOUTDirFiles(
+$outpath);
my @infiles = grep { /(.*)\Q$insuffix\E$/; not exists $outfiles{$1} } 
+&GetINDirFiles($inpath);  
print "@infiles\n";

[download]

and it should be fast.

UPDATE 2: Here is the full story.

use strict;
use warnings;

sub GetINDirFiles {
        my ($path) = @_;
        opendir my $dir, $path or die $!;
        return grep {!/\_ACK_/} readdir $dir;
}

sub GetOUTDirFiles {
        my ($path) = @_;
        opendir my $dir, $path or die $!;
        return grep {/\_ACK.xml$/} readdir $dir;
}

# Main
my $inpath = "./IN";      
my $outpath = "./OUT";
my $outsuffix = "_ACK.xml";
my $insuffix = ".xml";     
my $timethreshold = 900;       # set time threshold in seconds (900 se
+conds equal 15 minutes)

my %outfiles = map { /(.*)\Q$outsuffix\E$/; $1 => 1 } &GetOUTDirFiles(
+$outpath);
my @infiles = grep { /(.*)\Q$insuffix\E$/; $1 and not exists $outfiles
+{$1} } &GetINDirFiles($inpath);  

my $currenttime = time;        # get current time from system (epoch t
+ime)
@infiles = grep { -f "$inpath/$_" and ( $currenttime - (stat "$inpath/
+$_" )[9] ) > $timethreshold } @infiles;

# now you have all input files w/o corresponding output file that are 
+older than 15 minutes
for (@infiles) {
        print "File $_ in $inpath directory was created ". ( $currentt
+ime - (stat "$inpath/$_" )[9] )/60.0 ."minutes ago.\n";
        # put your action here
}

[download]

In reply to Re^5: ignore list of files using readdir function by hdb
in thread ignore list of files using readdir function by kaka_2

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