Shell/Bash script 学习笔记

#!/bin/bash
echo "Hello World !"

chmod +x ./test.sh  #使脚本具有执行权限
./test.sh  #执行脚本

echo "What is your name?"
read PERSON
echo "Hello, $PERSON"

variableName="value"

yourName="einverne"
echo $yourName
echo ${yourName}

yourName="einverne"
echo "your name is ${yourName} !!"
yourName="Ein Verne"
echo "your name is ${yourName} !!"

yourName="einverne"
echo "your name is ${yourName} !!"
readonly yourName
yourName="Ein Verne"

your name is einverne !!
./demo.sh: line 25: yourName: readonly variable

unset variableName

set -o nounset                              # Treat unset variables as an error

echo "File name is $0"
echo "First parameter : $1"
echo "First parameter : $2"
echo "This script have $# parameters"
echo "They are $*"
echo "They are $@"

for var in "$*"
do
    echo "${var}"
done

for var in "$@"
do
    echo "${var}"
done

./demo.sh p1 p2
File name is ./demo.sh
First parameter : p1
First parameter : p2
This script have 2 parameters
They are p1 p2
They are p1 p2
p1 p2
p1
p2

Data=`date`
echo "Date is ${Date}"

#!/bin/sh

a=10
b=20
val=`expr $a + $b`
echo "a + b : $val"

val=`expr $a - $b`
echo "a - b : $val"

val=`expr $a \* $b`
echo "a * b : $val"

val=`expr $b / $a`
echo "b / a : $val"

val=`expr $b % $a`
echo "b % a : $val"

if [ $a == $b ]
then
   echo "a is equal to b"
fi

if [ $a != $b ]
then
   echo "a is not equal to b"
fi

# 单引号中的任何字符都原样输出
# 单引号中不能出现单引号
echo '${hi}: "einverne"\t\n\r'

# 双引号可以有变量
# 双引号可以出现转义字符

yourName='einverne'
hi="hi, ${yourName} !\n"

# 字符长度
echo "your name length: ${#yourName}"

echo "first two character of your name ${yourName:0:2}"

text="0123456789-0123456789"
echo $text
echo '${text:position}' "${text:1}"
echo '${text:position:length}' "${text:1:3}"
# 从变量 $string 的开头，删除最短匹配 $substring 的子串
echo '${text#01}' "${text#01}"
# 从变量 $string 的开头，删除最长匹配 $substring 的子串
echo '${text##01}' "${text##01}"
# 从变量 $string 的结尾，删除最短匹配 $substring 的子串
echo '${text%89}' "${text%89}"
# 从变量 $string 的结尾，删除最长匹配 $substring 的子串
echo '${text%%89}' "${text%%89}"

# 使用 $replacement, 来代替第一个匹配的 $substring
echo '${text/substring/replacement} ${text/01/ab}' "${text/01/ab}"
# 使用 $replacement, 代替所有匹配的 $substring
echo '${text//substring/replacement} ${text//01/ab}' "${text//01/ab}"

# 如果 $string 的前缀匹配 $substring, 那么就用 $replacement 来代替匹配到的 $substring
echo '${text/#substring/replacement} ${text/#01/ab}' "${text/#01/ab}"

# 如果 $string 的后缀匹配 $substring, 那么就用 $replacement 来代替匹配到的 $substring
echo '${text/%substring/replacement} ${text/%01/ab}' "${text/%01/ab}"

array_name=(value0 value1 value2 value3)
# 或者
array_name=(
value0
value1
value2
value3
)
# 或者
array_name[0]=value0
array_name[1]=value1
array_name[2]=value2
# 读取数组
valuen=${array_name[2]}
# 获取所有元素
${array_name[*]}
${array_name[@]}
# 长度
# 取得数组元素的个数
length=${#array_name[@]}
# 或者
length=${#array_name[*]}
# 取得数组单个元素的长度
lengthn=${#array_name[n]}

test EXPRESSION

[ EXPRESSION ]

if [ expression ]
then
   Statement(s) to be executed if expression is true
fi


if [ expression ]
then
   Statement(s) to be executed if expression is true
else
   Statement(s) to be executed if expression is not true
fi

# 更复杂
if [ expression 1 ]
then
   Statement(s) to be executed if expression 1 is true
elif [ expression 2 ]
then
   Statement(s) to be executed if expression 2 is true
elif [ expression 3 ]
then
   Statement(s) to be executed if expression 3 is true
else
   Statement(s) to be executed if no expression is true
fi

echo 'Input a number between 1 to 4'
echo 'Your number is:\c'
read aNum
case $aNum in
    1)  echo 'You select 1'
    ;;
    2)  echo 'You select 2'
    ;;
    3)  echo 'You select 3'
    ;;
    4)  echo 'You select 4'
    ;;
    *)  echo 'You do not select a number between 1 to 4'
    ;;
esac

for 变量 in 列表
do
    command1
    command2
    ...
    commandN
done

sum=0
for ((i=1; i < 10; i++))
do
((sum=$sum+$i))
done

echo "sum=$sum"

while condition
do
   Statement(s) to be executed if command is true
done

i=0
sum=0
while [ $i -lt 10 ]
do
    (( i++ ))
    (( sum=$sum+$i ))
    echo "i=$i"
done

echo "sum=$sum"

until condition
command 1
...
done

i=0
sum=0
until [ $i -ge 10 ]
do
    (( i++ ))
    (( sum=$sum+$i ))
    echo "i=$i"
done

echo "sum=$sum"

function function_name () {
    list of commands
    [ return value ]
}