my $inFH;

if ( defined($infile) ) {

  open my $inFH, '<', $infile or die "opening input file $infile, $!";
}
my $instr;
{ local $/ = undef; $instr = <$inFH> }
if ( defined($instr) ) {

  say "input  is $instr";

}

##</code><code>##

my $instr;
if ( defined($infile) ) {
  my $inFH;
  open $inFH, '<', $infile or die "opening input file $infile, $!";
  { local $/ = undef; $instr = <$inFH> } close $inFH; # just polite to close it
}

if ( defined($instr) ) {

  say "input  is $instr";

} else { die "sorry, you did not specify an input either via a file or via [other ways of specifying an instr] " }