#use strict;
#use warnings;

my @_lines = <<LINES;
ABC in the first line
but not the second
LINES

foreach my $line (@_lines) {
    my $templine = $_line;
    print "$templine";
    # or  print "$line";
    if ($templine =~ /(ABC)/) {print "$1 = the line (1)";}
}

foreach my $_line (@_lines) {
    my $templine = $_line;
    ############   print "$templine";
    ############   # or  print "$line";
    if ($templine =~ /(ABC)/) {print "$1 = the line (2)";}
}