Unix Shell 基本语法

#!/bin/bash

#!/usr/bin/env zsh

key="value" # 普通字符串变量

echo ${key} # value
echo $key # value

unset key
echo ${key-$SHELL} # /bin/zsh
key=
echo ${key-$SHELL} # ""
key="value"
echo ${key-$SHELL} # value

unset key
echo ${key:-$SHELL} # /bin/zsh
key=
echo ${key:-$SHELL} # /bin/zsh
key="value"
echo ${key:-$SHELL} # value

unset key
echo ${key+$SHELL} # ""
key=
echo ${key+$SHELL} # /bin/zsh
key="value"
echo ${key+$SHELL} # /bin/zsh

unset key
echo ${key:+$SHELL} # ""
key=
echo ${key:+$SHELL} # ""
key="value"
echo ${key:+$SHELL} # /bin/zsh

unset key
echo ${key?"not define"} # zsh: key: "not define"
key=
echo ${key?"not define"} # ""
key="value"
echo ${key?"not define"} # value

unset key
echo ${key:?"not define"} # zsh: key: "not define"
key=
echo ${key:?"not define"} # zsh: key: "not define"
key="value"
echo ${key:?"not define"} # value

echo ${!h*} # http_proxy https_proxy

/etc/profile

PATH=$PATH:$JAVA_HOME/bin

~/.bash_profile

num=100
echo "$num+1" # 100+1

test $num -eq 100 && echo y || echo n # y
test $num = 100 && echo y || echo n # y

a=1
b=2
echo $[ $a + $b ] # 3
echo `expr $a + $b` # 3
echo $(expr $b - $a) # 1
echo $(( $num + 1 )) # 2
echo $((a+b)) / $(($a+$b)) # 3 / 3
echo $(expr $((a+b)) / $(($a+$b))) # 1

str="foo"

arr=(a b c)
# 只给第 3、5、10 个元素赋值，数组长度为 3
arr=([3]=24 [5]=19 [10]=12)

# 取出数组值
echo ${arr[1]} # a
# 数组切片
echo ${arr[1,2]} # a b
echo ${arr[*]:1:2} # H c  不推荐
# 数组长度
echo ${#arr[@]} # 3
# 输出数组为字符串
echo "$arr" # zsh 中输出整个数组 a b c  bash 中数组第一个元素 a
# 输出数组中的每个元素
echo ${arr[@]}
# 数组赋值
arr[2]="H"
echo ${arr[@]} # a H c
# 删除元素
unset arr[1] # 仅 bash 中生效
echo ${arr[@]} # H c
# 合并数组
arr1=(23 56)
arr2=(99 "shell")
arr_new=(${arr1[@]} ${arr2[*]})
echo ${arr_new[@]} # 23 56 99 shell

declare -A myMap=(
    [one]="first"
    [two]="second"
)

for item in ${myMap[*]}; do
        echo $item
done
# first
# second

# 单分支 if 语句
if [ condition ];then
  #body
fi

# 多分支 if 语句
if [ condition ]
then
  #body
else
  #body
fi

if [ condition ]
then
  #body
elif [ condition ]
then
  #body
else
  #body
fi

# 且关系
if [ condition1 ] && [ condition2 ]; then
  #body
fi

if [ condition1 -a condition2 ]; then
  #body
fi

# 或关系
if [ condition1 ] || [ condition2 ]; then
  #body
fi

if [ condition1 -o condition2]; then
  #body
fi

if test 1 -eq 1; then
  echo "equal"
else
  echo "not equal"
fi

# equal

if [ 1 -eq 1 ]; then
  echo "equal"
else
  echo "not equal"
fi

# 高级条件表达式 支持 ==、!=、>=、<=、>、< 操作符
if ((1==1)); then
  echo "equal"
else
  echo "not equal"
fi

case "${item}" in
  1)
    echo "item = 1"
  ;;
  2|3)
    echo "item = 2 or item = 3"
  ;;
  *)
    echo "default (none of above)"
  ;;
esac

# 遍历集合
for item in {a,b,c}; do
  echo $item
done

# 遍历数组
for item in ${arr[@]}; do
  echo $item
done

# 指定循环次数
for((i=1;i<10;i++))
do
    执行的命令
done

# 使用序列
for num in $(seq 1 5); do
 printf $num
done

while [ condition ]; do
  # body
done