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修改或移除信号捕获
要想在脚本中的不同位置进行不同的信号捕获处理，只需重新使用带有新选项的 trap 命令即可：
$ cat trapmod.sh
#!/bin/bash
#Modifying a set trap
#
trap "echo ' Sorry...Ctrl-C is trapped.'" SIGINT
#
count=1
while [ $count -le 3 ]
do echo "Loop #$count" sleep 1 count=$[ $count + 1 ]
done
#
trap "echo ' I have modified the trap!'" SIGINT
#
count=1
while [ $count -le 3 ]
do echo "Second Loop #$count" sleep 1 count=$[ $count + 1 ]
done
#
exit
$
修改了信号捕获之后，脚本处理信号的方式就会发生变化。但如果信号是在捕获被修改前接
收到的，则脚本仍然会根据原先的 trap 命令处理该信号。
$ ./trapmod.sh
Loop #1
^C Sorry...Ctrl-C is trapped.
Loop #2
Loop #3
Second Loop #1
Second Loop #2
^C I have modified the trap!
Second Loop #3
$ 也可以移除已设置好的信号捕获。在 trap 命令与希望恢复默认行为的信号列表之间加上两个连字符即可。
$ cat trapremoval.sh
#!/bin/bash
#Removing a set trap
#
trap "echo ' Sorry...Ctrl-C is trapped.'" SIGINT
#
count=1
while [ $count -le 3 ]
do echo "Loop #$count" sleep 1 count=$[ $count + 1 ]
done
#
trap -- SIGINT
echo "The trap is now removed."
#
count=1
while [ $count -le 3 ]
do echo "Second Loop #$count" sleep 1 count=$[ $count + 1 ]
done
#
exit
$
移除信号捕获后，脚本会按照默认行为处理 SIGINT 信号，也就是终止脚本运行。但如果信号是在捕获被移除前接收到的，
那么脚本就会按照原先 trap 命令中的设置进行处理：
$ ./trapremoval.sh
Loop #1
Loop #2
^C Sorry...Ctrl-C is trapped.
Loop #3
The trap is now removed.
Second Loop #1
Second Loop #2
^C
$