use strict;
use warnings;

# Read data into an array
open my $fh, "<", "input.txt";
my @strings = ();
while (my $line = <$fh>) {
    chomp $line;
    push @strings, $line;
}
close $fh;

# Replace trailing _in and _out
foreach my $line (@strings) {
    $line =~ s/\_in$|\_out$//;
}

# Output to STDOUT
foreach my $line (@strings) {
    print $line, "\n";
}