Bash 編程 10分鐘教學

參考: https://seankross.com/the-unix-workbench/bash-programming.html

0x01 數學

expr  5 / 2
# 2
echo "5/2" | bc -l
# 2.50000000000000000000

0x02 變量

a=1
let a=$a+1
# 2

##### $() 命令行計算結果
files=$(ll|wc -l)       
echo $files
# 365

##### 入參變量
#!/usr/local/bin/bash
echo "arguments: $@"
echo "arg1 : $1, arg2 : $2"
echo "arg count : $#"

# ./demo.sh aa bb
# arguments: aa bb
# arg1 : aa, arg2 : bb
# arg count : 2


##### 用戶輸入
read count
echo "Your input : $count"
# hello
# Your input: hello

##### 執行結果
true
echo $?
false
echo $?
# 0
# 1

##### 條件與或 && ||

##### 條件判斷
[[ 4 -gt 3 ]]
echo $?
# 0

Logical Flag	Meaning	Usage
-gt	大於	[[ $planets -gt 8 ]]
-ge	大於等於	[[ $votes -ge 270 ]]
-eq	等於 (數字或字符串)	[[ $fingers -eq 10 ]]
-ne	不等於	[[ $pages -ne 0 ]]
-le	小於等於	[[ $candles -le 9 ]]
-lt	小於	[[ $wives -lt 2 ]]
-e	文件存在	[[ -e $taxes_2016 ]]
-d	目錄存在	[[ -d $photos ]]
-z	Length of String is Zero	[[ -z $name ]]
-n	Length of String is Non-Zero	[[ -n $name ]]

0x03 正則匹配

bash 不支持 \d \D \s \S \w \W
需要使用下面代替:

[[:digit:]]，[^[:digit:]]，[[:space:]]，[^[:space:]]， [_[:alnum:]], [^_[:alnum:]]

• =~ 正則匹配 [[ $consonants =~ [aeiou] ]]
• = 字符串相等 [[ $password = "pegasus" ]]
• != 字符串不等 [[ $fruit != "banana" ]]
• ! 邏輯取反 [[ ! "apple" =~ ^b ]]

0x04 IF-ELSE

if [[ $1 -eq 4 ]]
then
  echo "$1 is my favorite number"
elif [[ $1 -gt 3 ]]
then
  echo "$1 is a great number"
else
  echo "You entered: $1, not what I was looking for."
fi

0x05 數組

# 定義數組
fruits=(apple banana orange)
# 使用數組元素
echo ${fruits[0]}

fruits=(blood frogs lice flies sickness boils hail locusts darkness death)

# 打印所有元素
echo ${fruits[*]}

# Slice index:5 length:3
echo ${fruits[*]:5:3}

# 打印數組長度
echo ${#fruits[*]}

# 拼接新數組  +=
fruits+=(apple banana)
echo ${fruits[*]}

fruits+=(pear)
echo ${fruits[*]}

# blood frogs lice flies sickness boils hail locusts darkness death
# boils hail locusts
# 10
# blood frogs lice flies sickness boils hail locusts darkness death apple banana
# blood frogs lice flies sickness boils hail locusts darkness death apple banana pear

0x06 括號

可以生成字符串序列

echo {0..3}
# echo {a..z}{A..Z}
# 0 1 2 3

0x07 循環

• for

for i in {0..3}
do
  echo "i is equal to $i"
done
# i is equal to 0
# i is equal to 1
# i is equal to 2
# i is equal to 3


words=(sunny wendy randy jobs)
for a in ${words[*]}
do
  echo "now word is : $a"
done

# now word is : sunny
# now word is : wendy
# now word is : randy
# now word is : jobs


files=$(ls)
for a in ${files[*]}
do
  echo "當前目錄文件名 : $a"
done

• while

count=3
while [[ $count -gt 0 ]]
do
  echo "count now is $count"
  let count=$count-1
done

# count now is 3
# count now is 2
# count now is 1

0x08 函數

function hello() {
  echo "Hello"
}

# 這裏兩次調用函數
hello
hello

# Hello
# Hello

# 注意函數名後面的括號可以省掉
function hello2 {
  echo "Nice to meet you $1"
}

hello2 小野花
# Nice to meet you 小野花


# 函數返回值
function do_sum {
  # 防止污染全局變量 sum
  local sum=0
  for i in $@
  do
    let sum=$sum+$i
  done
  echo $sum
}

# 需要注意: 如何想從函數接收返回值, 需要使用 $()語法
t=$(do_sum {1..5})
echo "result is $t"

# result is 15

接下來看什麼?

• Google Shell Guide