shell 移除信号捕获

本例中用到的trap命令会在每次检测到SIGINT信号时显示一行简单的文本消息。捕获这些信号会阻止用户用bash shell组合键Ctrl+C来停止程序

code

macname@MacdeMacBook-Pro Desktop % cat test.sh 
#!/bin/bash
# Testing signal trapping
#
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 "This is the end of the test script"
#%                                                                                                                                                                                              
macname@MacdeMacBook-Pro Desktop % 
macname@MacdeMacBook-Pro Desktop % ./test.sh
This is a test script
Loop #1
Loop #2
^C Sorry! I have trapped Ctrl-C
Loop #3
Loop #4
Loop #5
^C Sorry! I have trapped Ctrl-C
Loop #6
Loop #7
^C Sorry! I have trapped Ctrl-C
Loop #8
Loop #9
Loop #10
This is the end of the test script
macname@MacdeMacBook-Pro Desktop % 

移除信号捕获后，脚本按照默认行为来处理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，那么脚本会按照原先trap命令中的设置进行处理。

macname@MacdeMacBook-Pro Desktop % ./test.sh
Loop #1
Loop #2
Loop #3
^C Sorry... Ctrl-C is trapped.
Loop #4
Loop #5
I just removed the trap
Second Loop #1
Second Loop #2
Second Loop #3
^C
macname@MacdeMacBook-Pro Desktop % cat test.sh 
#!/bin/bash
# Removing a set trap

trap "echo ' Sorry... Ctrl-C is trapped.'" SIGINT
count=1
while [ $count -le 5 ] 
do
   echo "Loop #$count"
   sleep 1
   count=$[ $count + 1 ]
done
#
# Remove the trap
trap -- SIGINT
echo "I just removed the trap"
count=1
while [ $count -le 5 ]
do
   echo "Second Loop #$count"
   sleep 1
   count=$[ $count + 1 ]
done

macname@MacdeMacBook-Pro Desktop % 

 当脚本运行到正常的退出位置时，捕获就被触发了，shell会执行在trap命令行指定的命令。 如果提前退出脚本，同样能够捕获到EXIT。

macname@MacdeMacBook-Pro Desktop % ./test.sh
Loop #1
Loop #2
Loop #3
Loop #4
Loop #5
Goodbye...
macname@MacdeMacBook-Pro Desktop % ./test.sh
Loop #1
Loop #2
^CGoodbye...

macname@MacdeMacBook-Pro Desktop % cat test.sh 
#!/bin/bash
# Trapping the script exit #
trap "echo Goodbye..." EXIT #
count=1
while [ $count -le 5 ]
do
    echo "Loop #$count"
    sleep 1
    count=$[ $count + 1 ]
done%                                                                                                                                                                                           
macname@MacdeMacBook-Pro Desktop %