Linux信号
Linux系统利用信号与系统中的进程进行通信。Linux的常见信号有：
| 信号 | 值 | 描述 |
|---|---|---|
| 1 | SIGHUP | 挂起进程 |
| 2 | SIGINT | 终止进程 |
| 3 | SIGQUIT | 停止进程 |
| 9 | SIGKILL | 无条件终止进程 |
| 15 | SIGTERM | 尽可能终止进程 |
| 17 | SIGSTOP | 无条件停止进程，但不是终止进程 |
| 18 | SIGTSTP | 停止或暂停进程，但不终止进程 |
| 19 | SIGCONT | 继续运行停止的进程 |
信号组合键
Ctrl+C组合键会产生SIGINT信号，Ctrl+Z会产生SIGTSTP信号。
trap命令
trap命令允许你来指定shell脚本要监视并拦截的Linux信号。trap命令的格式为：trap commands signals。
demo：
#!/bin/bash
# test trap command
trap "echo 'Sorry! I have trapped Ctrl-C'" SIGINT
echo This is a test script
count=1
while [ $count -le 10 ]
do
echo "Loop $count"
sleep 1
count=$[ $count + 1 ]
done
echo The end.
运行结果：
This is a test script
Loop 1
Loop 2
^CSorry! I have trapped Ctrl-C
Loop 3
Loop 4
^CSorry! I have trapped Ctrl-C
Loop 5
Loop 6
Loop 7
Loop 8
^CSorry! I have trapped Ctrl-C
Loop 9
Loop 10
The end.
除了在shell脚本中捕获信号外，也可以在shell退出时捕获，在trap命令后加上EXIT信号就行。
#!/bin/bash
# test trap command
trap "echo Goodbye." EXIT
echo This is a test script
count=1
while [ $count -le 10 ]
do
echo "Loop $count"
sleep 1
count=$[ $count + 1 ]
done
echo The end.
运行结果：
This is a test script
Loop 1
Loop 2
Loop 3
Loop 4
Loop 5
Loop 6
Loop 7
Loop 8
Loop 9
Loop 10
The end.
Goodbye.
修改trap操作：
#!/bin/bash
# test trap command
trap "echo 'Sorry! I have trapped Ctrl-C'" SIGINT
count=1
while [ $count -le 5 ]
do
echo "Loop $count"
sleep 1
count=$[ $count + 1 ]
done
trap "echo 'Sorry! The trap has been modified.'" SIGINT
count=1
while [ $count -le 5 ]
do
echo "Loop $count"
sleep 1
count=$[ $count + 1 ]
done
echo The end.
运行结果：
Loop 1
Loop 2
Loop 3
^CSorry! I have trapped Ctrl-C
Loop 4
Loop 5
Loop 1
Loop 2
Loop 3
^CSorry! The trap has been modified.
Loop 4
Loop 5
The end.
可以删除捕获，命令形式为：trap – ***，例如trap – SIGINT
