经常遇到需要查看某个进程是否存在的情况下才会做出某些操作，例如我遇到的情况，查看某个进程存在，则去发送探测命令，如果不存在则直接不发送了。还有在停止指定进程时，经常使用如下命令
kill `ps aux | grep -w program_name | grep -v grep | awk '{print $2}'`
使用 pgrep 和 pkill 可以简单的实现
PGREP(1) Linux User’s Manual PGREP(1)
NAME
pgrep, pkill - look up or signal processes based on name and other attributes
SYNOPSIS
pgrep [-flvx] [-d delimiter] [-n|-o] [-P ppid,...] [-g pgrp,...]
[-s sid,...] [-u euid,...] [-U uid,...] [-G gid,...]
[-t term,...] [pattern]
pkill [-signal] [-fvx] [-n|-o] [-P ppid,...] [-g pgrp,...]
[-s sid,...] [-u euid,...] [-U uid,...] [-G gid,...]
[-t term,...] [pattern]
DESCRIPTION
pgrep looks through the currently running processes and lists the process IDs which matches the selection criteria to stdout. All the criteria have to match. For example,
pgrep -u root sshd
will only list the processes called sshd AND owned by root. On the other hand,
pgrep -u root,daemon
will list the processes owned by root OR daemon.
pkill will send the specified signal (by default SIGTERM) to each process instead of listing them on stdout.
OPTIONS
-d delimiter
Sets the string used to delimit each process ID in the output (by default a newline). (pgrep only.)
-f The pattern is normally only matched against the process name. When -f is set, the full command line is used.
-g pgrp,...
Only match processes in the process group IDs listed. Process group 0 is translated into pgrep’s or pkill’s own process group.
-G gid,...
Only match processes whose real group ID is listed. Either the numerical or symbolical value may be used.
-l List the process name as well as the process ID. (pgrep only.)
-n Select only the newest (most recently started) of the matching processes.
-o Select only the oldest (least recently started) of the matching processes.
-P ppid,...
Only match processes whose parent process ID is listed.
-s sid,...
Only match processes whose process session ID is listed. Session ID 0 is translated into pgrep’s or pkill’s own session ID.
-t term,...
Only match processes whose controlling terminal is listed. The terminal name should be specified without the "/dev/" prefix.
-u euid,...
Only match processes whose effective user ID is listed. Either the numerical or symbolical value may be used.
-U uid,...
Only match processes whose real user ID is listed. Either the numerical or symbolical value may be used.
-v Negates the matching.
-x Only match processes whose name (or command line if -f is specified) exactly match the pattern.
-signal
Defines the signal to send to each matched process. Either the numeric or the symbolic signal name can be used. (pkill only.)
OPERANDS
pattern
Specifies an Extended Regular Expression for matching against the process names or command lines.
EXAMPLES
Example 1: Find the process ID of the named daemon:
unix$ pgrep -u root named
Example 2: Make syslog reread its configuration file:
unix$ pkill -HUP syslogd
Example 3: Give detailed information on all xterm processes:
unix$ ps -fp $(pgrep -d, -x xterm)
Example 4: Make all netscape processes run nicer:
unix$ renice +4 ‘pgrep netscape‘
EXIT STATUS
0 One or more processes matched the criteria.
1 No processes matched.
2 Syntax error in the command line.
3 Fatal error: out of memory etc.
NOTES
The process name used for matching is limited to the 15 characters present in the output of /proc/pid/stat. Use the -f option to match against the complete command line,
/proc/pid/cmdline.
The running pgrep or pkill process will never report itself as a match.
BUGS
The options -n and -o and -v can not be combined. Let me know if you need to do this.
Defunct processes are reported.
SEE ALSO
ps(1) regex(7) signal(7) killall(1) skill(1) kill(1) kill(2)
STANDARDS
pkill and pgrep were introduced in Sun’s Solaris 7. This implementation is fully compatible.
监控一个进程，不存在则将其启动
while [1 -eq 1] #死循环
do
for procname in proc1 proc2 #需要检测的进程名字
do
pgrep $procname
if [0 -ne $? ] #如果进程不存在就重启它
then
./$prconame
fi
done
sleep 10
done &
pgrep 根据给出的进程名判断是否有这个名字的进程。如果有这个名字的进程正常退出，退出值0.如果没有这个名字的进程异常退出，退出值1。最后加 & 符号，表示让脚本在后台执行，即将shell关闭后 程序仍在运行
