$echo -e "1\n2\n3" > 1
$strace -f -e trace=execve xargs -n1 /bin/echo < 1
execve("/usr/bin/xargs", ["xargs", "-n1", "/bin/echo"], [/* 15 vars */]) = 0
Process 3184 attached
[pid 3184] execve("/bin/echo", ["/bin/echo", "1"], [/* 15 vars */]) = 0
1
[pid 3184] +++ exited with 0 +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=3184, si_uid=1015, si_status=0, si_utime=0, si_stime=0} ---
Process 3185 attached
[pid 3185] execve("/bin/echo", ["/bin/echo", "2"], [/* 15 vars */]) = 0
2
[pid 3185] +++ exited with 0 +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=3185, si_uid=1015, si_status=0, si_utime=0, si_stime=0} ---
Process 3186 attached
[pid 3186] execve("/bin/echo", ["/bin/echo", "3"], [/* 15 vars */]) = 0
3
[pid 3186] +++ exited with 0 +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=3186, si_uid=1015, si_status=0, si_utime=0, si_stime=0} ---
+++ exited with 0 +++
$
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Почитайте про дело Дмитрия Богатова.