shell學習之信號的捕捉（trap）

信號

linux通過信號來在運行在系統上的進程之間通信也可以通過信號來控制shell腳本的運行

（1）捕捉信號：trap命令

• 常用信號 ctrl+c（終止進程） ctrl+z（暫停進程，打入後臺）

[root@server ~]# trap "echo westos" 2
[root@server ~]# ^Cwestos

（2）列出中斷信號與鍵盤的關係

[root@server ~]# stty -a
speed 38400 baud; rows 24; columns 80; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>;
eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R;
werase = ^W; lnext = ^V; flush = ^O; min = 1; time = 0;
-parenb -parodd -cmspar cs8 -hupcl -cstopb cread -clocal -crtscts
-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon -ixoff
-iuclc -ixany -imaxbel -iutf8
opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0
isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt
echoctl echoke

（3）信號屏蔽

[root@server ~]# trap "" 2	##信號屏蔽
[root@server ~]# trap : 2	##恢復信號

（4）腳本形式：

#!/bin/bash

trap "echo 'Sorry!I have trapped Ctrl+C'" 2
echo "This is a test script~"

count=1

while [ $count -le 10 ]
do
    echo "Loop #$count"
    sleep 2
    count=$[ $count + 1 ]
done

echo "This is the end of the script~"
trap - 2    ##恢復
echo "I just removed the trap"

（5）捕捉腳本的退出

[root@server ~]# cat trap.sh 
trap "echo ByeBye~" EXIT

count=1
while [ $count -le 5 ]
do
    echo "Loop #$count"
    sleep 2
    count=$[ $count + 1 ]
done
[root@server ~]# sh trap.sh 
Loop #1
Loop #2
Loop #3
^CByeBye~

（6）練習

• 執行腳本時，使用ctrl+c可以將/tmp/westos下建立的文件都刪除掉

#!/bin/bash

trap "find /tmp -type f -name "westos_*" | xargs rm -f && exit " 2

while true
do
    touch /tmp/westos_$(date +%F-%N-%M-%S)
    sleep 2
    ls -l /tmp/westos*
done