bash判断进程存在的3种方法

当前系统中的进程：
apple@ubuntu:~$ ps -ef
UID PID PPID C STIME TTY TIME CMD
root 1 0 0 13:57 ? 00:00:02 /sbin/init
root 2 0 0 13:57 ? 00:00:00 [kthreadd]
root 3 2 0 13:57 ? 00:00:00 [migration/0]
root 4 2 0 13:57 ? 00:00:00 [ksoftirqd/0]
root 5 2 0 13:57 ? 00:00:00 [watchdog/0]
root 6 2 0 13:57 ? 00:00:00 [migration/1]
root 7 2 0 13:57 ? 00:00:00 [ksoftirqd/1]
root 8 2 0 13:57 ? 00:00:00 [watchdog/1]
root 9 2 0 13:57 ? 00:00:00 [events/0]
root 10 2 0 13:57 ? 00:00:00 [events/1]
root 11 2 0 13:57 ? 00:00:00 [khelper]
root 12 2 0 13:57 ? 00:00:00 [kstop/0]
root 13 2 0 13:57 ? 00:00:00 [kstop/1]
root 14 2 0 13:57 ? 00:00:00 [kintegrityd/0]
root 15 2 0 13:57 ? 00:00:00 [kintegrityd/1]
root 16 2 0 13:57 ? 00:00:00 [kblockd/0]
root 17 2 0 13:57 ? 00:00:00 [kblockd/1]
root 18 2 0 13:57 ? 00:00:00 [kacpid]
root 19 2 0 13:57 ? 00:00:00 [kacpi_notify]
root 20 2 0 13:57 ? 00:00:00 [cqueue]
root 21 2 0 13:57 ? 00:00:00 [ata/0]
root 22 2 0 13:57 ? 00:00:00 [ata/1]
root 23 2 0 13:57 ? 00:00:00 [ata_aux]
root 24 2 0 13:57 ? 00:00:00 [ksuspend_usbd]
root 25 2 0 13:57 ? 00:00:00 [khubd]
root 26 2 0 13:57 ? 00:00:00 [kseriod]
root 27 2 0 13:57 ? 00:00:00 [kmmcd]
root 28 2 0 13:57 ? 00:00:00 [btaddconn]
root 29 2 0 13:57 ? 00:00:00 [btdelconn]
root 30 2 0 13:57 ? 00:00:00 [pdflush]
root 31 2 0 13:57 ? 00:00:00 [pdflush]
root 32 2 0 13:57 ? 00:00:00 [kswapd0]
root 33 2 0 13:57 ? 00:00:00 [aio/0]
root 34 2 0 13:57 ? 00:00:00 [aio/1]
root 35 2 0 13:57 ? 00:00:00 [ecryptfs-kthrea]
root 38 2 0 13:57 ? 00:00:00 [pciehpd]

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