SHELL下的trap命令SIGHUP信号

trap命令用来捕捉特定信号，并且指定捕获该信号的行为。
格式：
      trap commands signals
SIGHUP会在以下3种情况下被发送给相应的进程:
1、终端关闭时，该信号被发送到和shell进程同一个进程组的进程。
2、session首进程退出时，该信号被发送到该session中的前台进程组中的每一个进程
3、若父进程退出导致进程组成为孤儿进程组，且该进程组中有进程处于停止状态（收到SIGSTOP或SIGTSTP信号），该信号会被发送到该进程组中的每一个进程。

#!/bin/bash

count=1
cat /dev/null > ~/test/shell/signal/wgw_hup
cat /dev/null > ~/test/shell/signal/recv_hup
trap "echo 'SIGHUP signal' > ~/test/shell/signal/wgw_hup" SIGHUP
while [ $count -le 10 ]
do
    echo "Loop #$count" >> ~/test/shell/signal/recv_hup
    sleep 5
    count=$[ $count + 1 ]
done

echo "exiting....." >> ~/test/shell/signal/recv_hup

1.执行脚本
   sh sighup.sh
  操作：关闭终端
  结果：         

[e-mail]:~/test/shell/signal>more recv_hup
Loop #1
Loop #2
Loop #3
Loop #4
Loop #5
Loop #6
Loop #7
Loop #8
Loop #9
Loop #10
exiting.....
[e-mail]:~/test/shell/signal>more wgw_hup
SIGHUP signal

[e-mail]:~/test/pipe>ps -ef | grep sighup
gwwu      8175  7943  0 11:18 pts/16   00:00:00 sh sighup.sh
gwwu      8184 30681  0 11:18 pts/7    00:00:00 grep sighup
[e-mail]:~/test/pipe>ps -ef | grep sighup-----------关闭终端后，原先的进程变成daemon进程。
gwwu      8175     1  0 11:18 ? 00:00:00 sh sighup.sh
gwwu      8189 30681  0 11:18 pts/7    00:00:00 grep sighup

2. 执行脚本
  sh sighup.sh &
  操作：关闭终端
  结果： 

[e-mail]:~/test/shell/signal>more recv_hup
Loop #1
Loop #2
Loop #3
Loop #4
Loop #5
Loop #6
Loop #7
Loop #8
Loop #9
Loop #10
exiting.....
[e-mail]:~/test/shell/signal>more wgw_hup
SIGHUP signal

[e-mail]:~/codes/istanbul_2_9>ps -ef | grep sighup
gwwu     26204 23029  0 11:21 pts/3    00:00:00 sh sighup.sh
gwwu     26245 26218  0 11:21 pts/6    00:00:00 grep sighup
[e-mail]:~/codes/istanbul_2_9>ps -ef | grep sighup----------关闭终端后shell进程仍然存在
gwwu     26204     1  0 11:21 ?        00:00:00 sh sighup.sh
gwwu     26249 26218  0 11:21 pts/6    00:00:00 grep sighup
[e-mail]:~/codes/istanbul_2_9>ps -ef | grep sighup
gwwu     26204     1  0 11:21 ?        00:00:00 sh sighup.sh
gwwu     26251 26218  0 11:21 pts/6    00:00:00 grep sighup

3.将脚本中的trap行去掉

#!/bin/bash

count=1
cat /dev/null > ~/test/shell/signal/wgw_hup
cat /dev/null > ~/test/shell/signal/recv_hup
while [ $count -le 10 ]
do
    echo "Loop #$count" >> ~/test/shell/signal/recv_hup
    sleep 5
    count=$[ $count + 1 ]
done

echo "exiting....." >> ~/test/shell/signal/recv_hup

执行sh sighup.sh 和sh sighup.sh &
关闭终端后进程直接退出

执行nohup sh sighhup.sh
关闭终端后进程仍然执行，直到进程结束。