В bash "echo" - это builtin. Выжимка strace ./hello_world.sh:

stat("./hello_world.sh", {st_mode=S_IFREG|0755, st_size=30, ...}) = 0
ioctl(3, TCGETS, 0x7ffecf9069c0)        = -1 ENOTTY (Inappropriate ioctl for device)
lseek(3, 0, SEEK_CUR)                   = 0
read(3, "#!/bin/bash\necho Hello World!\n", 80) = 30
lseek(3, 0, SEEK_SET)                   = 0
prlimit64(0, RLIMIT_NOFILE, NULL, {rlim_cur=16*1024, rlim_max=16*1024}) = 0
fcntl(255, F_GETFD)                     = -1 EBADF (Bad file descriptor)
dup2(3, 255)                            = 255
close(3)                                = 0
fcntl(255, F_SETFD, FD_CLOEXEC)         = 0
fcntl(255, F_GETFL)                     = 0x8000 (flags O_RDONLY|O_LARGEFILE)
fstat(255, {st_mode=S_IFREG|0755, st_size=30, ...}) = 0
lseek(255, 0, SEEK_CUR)                 = 0
read(255, "#!/bin/bash\necho Hello World!\n", 30) = 30
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0x1), ...}) = 0
write(1, "Hello World!\n", 13Hello World!
)          = 13
read(255, "", 30)                       = 0
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
exit_group(0)                           = ?
+++ exited with 0 +++