shell_ two

grammar

1. Judge

# [   ]  Leave a space on the left and right of the variable in the middle  

if [ -d $0 ]; then
    echo "this is dir"
elif [ -f $0 ]; then
    echo "this is file"
else
    echo "Nothing"
fi

2. loop

# seq : sequence: shell Sequence , Fully closed interval 

for  i in `seq 1 10`
do
    echo "current  num  is  $i"
done

 Equate to ：
for ((i=1; i<11; i++)); do echo "current num is $i"; done

3. function

foo() {
    echo "Hello Shell"
    for f in `ls ../`
    do 
        echo $f
    done
}

#  Calling a function does not require （）
foo

 Be careful ：
 When defining a function , Variable name preceded by  function  and   No addition  function  All right 

4. case: Execute the corresponding action statement when there are conditions that match , Otherwise, quit

cat   <<   EOF
 Please enter the operation number to be performed ：【1-4】
==========================
【1】 The system update 
【2】 Install the software 
【3】 install Redis
【4】 install Nginx
=========================
EOF

#  Get the operation number to be performed 
if  [[ -n $1 ]]; then
    input=$1
    echo " Perform the operation ： $1"
else
    read  -p  " Please select ： "  input
fi

case  $input  in
         1) system_update;;
         2) install_software;;
         3) install_redis;;
         4) install_nginx;;
         *) exit;;
esac