trap

语法

语法格式：trap [参数]

常用参数：

-l	打印信号列表
-p	打印与每一个信号有关联的命令的列表

1、捕获脚本中的异常

​ 可以捕获脚本中执行错误的命令，需要添加set -E，trap “echo 错误” ERR

例：

#!/bin/bash
set -E
trap 'echo 抓住非零返回值' ERR
sub()
{
ls dfqwefi
rm fwjepf
}

sub

2、捕获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	SIGHP	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

Ctrl+C组合键会产生SIGINT信号，Ctrl+Z会产生SIGTSTP信号。

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。

例1：

#!/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.

例2：

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.

例3：

#!/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.

例4：

删除捕获，命令形式为：trap - ***，例如trap - SIGINT

#!/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 - 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
^C