Bash three methods for judging the existence of a process

Article Title: bash three methods for judging the existence of a process. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.

Processes in the current system:
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 :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 :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]
Root 39 2 0 13:57? 00:00:00 [scsi_eh_0]
Root 40 2 0 13:57? 00:00:00 [scsi_eh_1]
Root 41 2 0 :57? 00:00:00 [kstriped]
Root 42 2 0 13:57? 00:00:00 [kmpathd/0]
Root 43 2 0 :57? 00:00:00 [kmpathd/1]
Root 44 2 0 :57? 00:00:00 [kmpath_handlerd]
Root 45 2 0 13:57? 00:00:00 [ksnapd]
Root 46 2 0 13:57? 00:00:00 [kondemand/0]
Root 47 2 0 13:57? 00:00:00 [kondemand/1]
Root 48 2 0 13:57? 00:00:00 [krfcommd]
Root 256 2 0? 00:00:00 [mpt_poll_0]
Root 717 2 0? 00:00:00 [scsi_eh_2]
Root 753 2 0? 00:00:00 [kdmflush]
Root 764 2 0? 00:00:00 [kdmflush]
Root 795 2 0? 00:00:00 [kjournald]
Root 915 1 0? 00:00:00/sbin/udevd -- daemon
Root 1617 2 0? 00:00:00 [kpsmoused]
Root 2166 1 0 00:00:00 tty4/sbin/getty 38400 tty4
Root 2167 1 0 00:00:00 tty5/sbin/getty 38400 tty5
Root 2172 1 0 00:00:00 tty2/sbin/getty 38400 tty2
Root 2173 1 0 00:00:00 tty3/sbin/getty 38400 tty3
Root 2174 1 0 00:00:00 tty6/sbin/getty 38400 tty6
Root 2244 1 0? 00:00:00/usr/sbin/acpid-c/etc/acpi/eve
Root 2259 1 0? 00:00:00/usr/sbin/syslog-ng-p/var/run/
105 2279 1 0? 00:00:00/bin/Alibaba-daemon -- system
Root 2311 1 0? 00:00:00/usr/sbin/incrond-f/etc/incron
Root 2381 1 0? 00:00:00 dhclient3-e IF_METRIC = 100-pf/
Root 2442 1 0? 00:00:00/usr/sbin/sshd
Root 2453 1 0? 00:00:00/usr/lib/postfix/master
Postfix 2465 2453 0? 00:00:00 pickup-l-t fifo-u-c
Postfix 2468 2453 0? 00:00:00 qmgr-l-t fifo-u
108 2472 1 0? 00:00:00/usr/sbin/hald
Root 2475 1 0? 00:00:00/usr/sbin/console-kit-daemon
Root 2538 2472 0? 00:00:00 hald-runner
Root 2567 2538 0? 00:00:00 hald-addon-input: Listening on/
Root 2594 2538 0? 00:00:00 hald-addon-storage: polling/dev
Root 2595 2538 0? 00:00:00 hald-addon-storage: no polling o
108 2600 2538 0? 00:00:00 hald-addon-acpi: listening on ac.
Daemon 2647 1 0 13:58? 00:00:00/usr/sbin/atd
Root 2672 1 0? 00:00:00/usr/sbin/cron
Root 2691 1 0 00:00:00 tty1/sbin/getty 38400 tty1
Root 2994 2442 0? 00:00:00 sshd: apple [priv]
Apple 3003 2994 0? 00:00:00 sshd: apple @ pts/0
Apple 3004 3003 1 00:00:00 pts/0-bash
Apple 3024 3004 0 00:00:00 pts/0 ps-ef

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