Perl で子プロセスが入力を読めない問題 ref: https://qiita.com/kaz-utashiro/items/80fc83e56e645f19e927

file0.txt

$_ = do { local $/; <> };
if (open(CHLD, '|-') == 0) {
    print <>;
    exit;
}
print CHLD $_;

file1.txt

$_ = do { local $/; <> };
if (open(CHLD, '|-') == 0) {
    exec "cat" or warn $!;
    exit;
}
print CHLD $_;

file2.txt

if (open(CHLD, '|-') == 0) {
    print <>;
    exit;
}
$_ = do { local $/; <> };
print CHLD $_;

file3.txt

@_ = <>;
if (open(CHLD, '|-') == 0) {
    print <>;
    exit;
}
print CHLD @_;

file4.txt

@_ = <>;
warn "eof\n" if eof STDIN;
if (open(CHLD, '|-') == 0) {
    print <>;
    exit;
}
print CHLD @_;

file5.txt

$_ = do { local $/; <> };
if (open(CHLD, '|-') == 0) {
    <> if eof STDIN;
    print <>;
    exit;
}
print CHLD $_;

file6.txt

$_ = do { local $/; <> };
if (open(CHLD, '|-') == 0) {
    open STDIN, '<&', 0 if eof STDIN;
    print <>;
    exit;
}
print CHLD $_;

file7.txt

$_ = do { local $/; <> };
pipe PIN, POUT or die;
if (fork == 0) {
    close STDIN;
    open STDIN, '<&PIN';
    close PIN;
    close POUT;
    print <>;
    exit;
}
close PIN;
print POUT $_;