$ strace ./944682.pl
...
nanosleep({1, 0}, {1, 0})               = 0
nanosleep({0, 0}, NULL)                 = 0
lseek(3, 0, SEEK_END)                   = 32
open("/tmp/xxx", O_RDONLY)              = 4
ioctl(4, SNDCTL_TMR_TIMEBASE or TCGETS, 0x7fff3d7d2c00) = -1 ENOTTY (Inappropriate ioctl for device)
lseek(4, 0, SEEK_CUR)                   = 0
fstat(4, {st_mode=S_IFREG|0644, st_size=32, ...}) = 0
fcntl(4, F_SETFD, FD_CLOEXEC)           = 0
fstat(4, {st_mode=S_IFREG|0644, st_size=32, ...}) = 0
close(4)                                = 0
lseek(3, 0, SEEK_END)                   = 32
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigaction(SIGCHLD, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
...

##</code><code>##

...
lseek(3, 72, SEEK_SET)                  = 72
read(3, "foo\n", 4)                     = 4
lseek(3, 0, SEEK_CUR)                   = 76
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigaction(SIGCHLD, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
nanosleep({1, 0}, {1, 0})               = 0
nanosleep({0, 0}, NULL)                 = 0
write(1, "foo\n", 4foo
)                    = 4
...