Shell programming

while loop

#!/bin/bash
i=1
sum=0
while ((i <= 100))
do
    ((sum += i))
    ((i++))
done
echo "The sum is: $sum"

Reference resources ：https://www.jb51.net/article/201771.htm

Number of lines read from the file

awk 'END{print NR}' test.sh 

Reference resources ：https://www.bilibili.com/read/cv16036091/

Read the last line of the file

tail -n 1 file.txt

Reference resources ：https://www.csdn.net/tags/MtzaEgysODk5NjMtYmxvZwO0O0OO0O0O.html

Read and execute statements

cmd=$line
 #  Print instructions 
 echo $cmd
 #  Execution instruction 
 echo $cmd | sh

Reference resources ：https://blog.csdn.net/u010132847/article/details/113141583

Delete last line

sed -i '$d' <file>

Reference resources ：https://blog.csdn.net/sosemseo/article/details/108356945

Append a line to the file

str='gg'
sed -i '$a\'$str /opt/b.txt

Reference resources ：https://blog.csdn.net/yabingshi_tech/article/details/114364672

bash Script nohup perform

nohup bash xxx.sh > xxx.log &