Bash cheatsheet

#!/bin/bash

VAR="world"
echo "Hello $VAR!" # => Hello world!

执行脚本

$ bash hello.sh # 以 bash 方式执行脚本 
$ sh hello.sh   # 以 sh 方式执行脚本
$ sh hell0.sh & # 以 后台 方式执行脚本

varname="John"           # 定义变量，索引号
varname='John'           # 定义变量，单引号
varname=`echo John`      # command赋值变量 用` `
varname=$(echo John)     # command赋值变量 用$()
varname = "John"         # => Error (=左右不能有空格)
var=                     # 空参数
unset var                # 取消变量
let foo=1+2              # 声明变量时，可以直接执行算术表达式。
readonly variable        # 只读变量
local variable           # 定义内部变量，仅在函数内使用
export VARNAME=value     # 定义环境变量

echo ${varname}    # => John (输出变量内容)
echo $varname      # => John (输出变量内容)
echo "$varname"    # => John (输出变量内容)
echo '$varname'    # => $varname (输出字符串)
echo "${varname}!" # => John! (输出变量内容)

# 这是一个内联的Bash注释. 单行注释

: '
This is a
multi line
comment
'

多行注释使用 :' 开始 和 ' 结尾

get_name() {
    echo "John"
}

echo "You are $(get_name)"

更多: 函数

if [[ -z "$string" ]]; then
    echo "String is empty"
elif [[ -n "$string" ]]; then
    echo "String is not empty"
fi

更多: Conditionals

echo {A,B}.js

更多: Brace expansion

# => I'm in /path/of/current
echo "I'm in $(PWD)"

# Same as:
echo "I'm in `pwd`"

更多: Command substitution

echo ${food:-Cake}  #=> $food or "Cake"

STR="/path/to/foo.cpp"
echo ${STR%.cpp}    # /path/to/foo
echo ${STR%.cpp}.o  # /path/to/foo.o
echo ${STR%/*}      # /path/to

echo ${STR##*.}     # cpp (获取文件后缀)
echo ${STR##*/}     # foo.cpp (文件名)

echo ${STR#*/}      # path/to/foo.cpp
echo ${STR##*/}     # foo.cpp

echo ${STR/foo/bar} # /path/to/bar.cpp

name="John"
echo ${name}           # => John
echo ${name:0:2}       # => Jo
echo ${name::2}        # => Jo
echo ${name::-1}       # => Joh
echo ${name:(-1)}      # => n
echo ${name:(-2)}      # => hn
echo ${name:(-2):2}    # => hn

length=2
echo ${name:0:length}  # => Jo

更多: Parameter expansion

STR="HELLO WORLD!"
echo ${STR,}   # => hELLO WORLD! 首字母小写
echo ${STR,,}  # => hello world! 全部小写

STR="hello world!"
echo ${STR^}   # => Hello world! 首字母大写
echo ${STR^^}  # => HELLO WORLD! 全部大写

ARR=(hello World)
echo "${ARR[@],}" # => hello world 数组中的所有元素首字母小写
echo "${ARR[@]^}" # => Hello World 数组中的所有元素首字母大写

~          # $HOME的值
~/foo      # $HOME/foo
~fred/foo  # 用户fred的主目录的foo子目录
~+/foo     # $PWD/foo
~-/foo     # ${OLDPWD-'~-'}/foo
~N         # 将显示一个'dirs +N'命令的结果字符串
~+N        # 将显示一个'dirs +N'命令的结果字符串
~-N        # 将显示一个'dirs -N'命令的结果字符串

arr_number=(1 2 3 4 5)             # 数值类型的数组
Fruits=('Apple' 'Banana' 'Orange') # 字符串类型数组

Fruits[0]="Apple"                  # 赋值
Fruits[1]="Banana"
Fruits[2]="Orange"

ARRAY1=(foo{1..2}) # => foo1 foo2
ARRAY2=({A..D})    # => A B C D

# 合并  => foo1 foo2 A B C D
ARRAY3=(${ARRAY1[@]} ${ARRAY2[@]})

# 声明构造
declare -a Numbers=(1 2 3)
Numbers+=(4 5) # 追加 => 1 2 3 4 5

Fruits=('Apple' 'Banana' 'Orange')

for e in "${Fruits[@]}"; do
    echo $e
done

let i=0
let j=${#Fruits[@]}-1
for (( i=0;i<j;i++,j-- ))
  do
    echo ${arr[i]}
done

#包含索引

for i in "${!Fruits[@]}"; do
  printf "%s\t%s\n" "$i" "${Fruits[$i]}"
done

function extract()
{
    local -n myarray=$1
    local idx=$2
    echo "${myarray[$idx]}"
}
Fruits=('Apple' 'Banana' 'Orange')
extract Fruits 2     # => Orangle

declare -A sounds # 定义字典
array=([2]=valC [0]=valA [1]=valB)  # 定义字典

sounds[dog]="bark"    # 赋值
sounds[cow]="moo"
sounds[bird]="tweet"
sounds[wolf]="howl"

echo ${sounds[dog]} # 输出指定dog元素的值
echo ${sounds[@]}   # 输出所有的value
echo ${!sounds[@]}  # 输出所有的key
echo ${#sounds[@]}  # 输出字典的数量
unset sounds[dog]   # 删除 dog

for val in "${sounds[@]}"; do
    echo $val
done

for key in "${!sounds[@]}"; do
    echo $key
done

# 写法一
test expression

# 写法二
[ expression ]

# 写法三
[[ expression ]]

# [ ] 单双括号
　# - [ ] 两个符号左右都要有空格分隔
　# - 内部操作符与操作变量之间要有空格：如  [  ]
　# - 字符串比较中，> < 需要写成\> \< 进行转义
　# - [ ] 中字符串或者${}变量尽量使用"" 双引号扩住，避免值未定义引用而出错的好办法
　# - [ ] 中可以使用 –a –o 进行逻辑运算

# [[ ]] 双方括号
　# [[ ]] 两个符号左右都要有空格分隔
　# 内部操作符与操作变量之间要有空格：如  [[ "a" = "b" ]]
　# 字符串比较中，可以直接使用 > < 无需转义
　# [[ ]] 中字符串或者${}变量尽量如未使用"" 双引号扩住的话，会进行模式和元字符匹配
　  # [[ "ab"=a* ]] && echo "ok"
　# [[] ] 内部可以使用 &&  || 进行逻辑运算

if [ "$1" = 'y' -a $2 -gt 0 ]; then
    echo "yes"
fi

if [ "$1" = 'n' -o $2 -lt 0 ]; then
    echo "no"
fi

# 以下表示的含义一致
[  exp1  -a exp2  ]
[[  exp1 && exp2 ]]
[  exp1  ] && [  exp2  ]
[[ exp1  ]] && [[  exp2 ]]

# 以下表示的含义一致
[  exp1  -o exp2  ]
[[  exp1 || exp2 ]]
[  exp1  ] || [  exp2  ]
[[ exp1  ]] || [[  exp2 ]]

# 三元表达式
[ -f /opt/file ] && echo 'file' || echo 'not file'     # 判断
[ -f /opt/file ] && (echo 'file'; echo 'shell') || echo 'not file'     # 子shell

for i in /etc/rc.*; do
    echo $i
done

for ((i = 0 ; i < 100 ; i++)); do
    echo $i
done

i=1
while [[ $i -lt 4 ]]; do
    echo "Number: $i"
    ((i++))
done

i=3
while [[ $i -gt 0 ]]; do
    echo "Number: $i"
    ((i--))
done

for number in $(seq 1 3); do
    if [[ $number == 2 ]]; then
        continue; # 跳出本次循环
    fi
    echo "$number"
done

for number in $(seq 1 3); do
    if [[ $number == 2 ]]; then
        break; # 跳出循环
    fi
    echo "$number"
done

select name [in list];
do
  statements that can use $name
done

select brand in Samsung Sony iphone symphony Walton
do
  echo "You have chosen $brand"
done

while [[ "$1" =~ ^- && ! "$1" == "--" ]]; do
case $1 in
  -V | --version )
    echo $version
    exit
    ;;
  -s | --string )
    shift; string=$1
    ;;
  -f | --flag )
    flag=1
    ;;
esac;
shift; # shift n 表示把第n+1个参数移到第1个参数, 即命令结束后$1的值等于$n+1的值
done

count=0
until [ $count -gt 10 ]; do
    echo "$count"
    ((count++))
done

until false; do echo 'Hi, until looping ...'; done

while true; do
    # here is some code.
done

#死循环 (简写)

while :; do
    # here is some code.
done

cat file.txt | while read line; do
    echo $line
done

< file.txt | while read line; do
  echo $line
done

myfunc() {
    echo "hello $1"
}

function myfunc() {
    echo "hello $1"
}

myfunc "John"

unset -f myfunc         # 删除定义的函数
declare -f myfunc       # 显示myfunc函数的定义内容

myfunc() {
    local myresult='some value'
    echo $myresult
}

result="$(myfunc)"

myfunc() {
    return 1 # 返回非0数字
}

if myfunc; then
    echo "success"
else
    echo "failure"
fi

trap 'command' 1 2 3 15
trap 'command' EXIT

trap 'echo "trapped."; exit 1' 1 2 3 15
trap '' 1 2 3 15   # 忽略信号处理

function egress {
  command1
  command2
  command3
}

trap egress EXIT   # 使用函数

# 处理脚本错误
trap 'echo Error at about $LINENO' ERR


traperr() {
    echo "ERROR: ${BASH_SOURCE[1]} at about ${BASH_LINENO[0]}"
}

set -o errtrace
trap traperr ERR

NOCOLOR='\033[0m'
RED='\033[0;31m'
GREEN='\033[0;32m'
ORANGE='\033[0;33m'
BLUE='\033[0;34m'
PURPLE='\033[0;35m'
CYAN='\033[0;36m'
LIGHTGRAY='\033[0;37m'
DARKGRAY='\033[1;30m'
LIGHTRED='\033[1;31m'
LIGHTGREEN='\033[1;32m'
YELLOW='\033[1;33m'
LIGHTBLUE='\033[1;34m'
LIGHTPURPLE='\033[1;35m'
LIGHTCYAN='\033[1;36m'
WHITE='\033[1;37m'

echo -e "The first five colors of the rainbow are ${RED}red ${ORANGE}orange ${YELLOW}yellow ${GREEN}green ${NOCOLOR}and ${BLUE}blue${NOCOLOR}"

export TERM=xterm
#　tput Color Capabilities:
tput setab [1-7] – Set a background color using ANSI escape
tput setb [1-7] – Set a background color
tput setaf [1-7] – Set a foreground color using ANSI escape
tput setf [1-7] – Set a foreground color

#　tput Text Mode Capabilities:
tput bold – Set bold mode
tput dim – turn on half-bright mode
tput smul – begin underline mode
tput rmul – exit underline mode
tput rev – Turn on reverse mode
tput smso – Enter standout mode (bold on rxvt)
tput rmso – Exit standout mode
tput sgr0 – Turn off all attributes

#　Color Code for tput:
0 – Black   1 – Red      2 – Green   3 – Yellow
4 – Blue    5 – Magenta  6 – Cyan    7 – White

# 第一种：$[]
# 第二种：$(())
# 第三种: expr
# 第四种：let

((i=$j+$k))     等价于   i=`expr $j + $k`
((i=$j-$k))     等价于   i=`expr $j -$k`
((i=$j*$k))     等价于   i=`expr $j \*$k`
((i=$j/$k))     等价于   i=`expr $j /$k`

+：加法
-：减法
*：乘法
/：除法（整除）
%：余数
**：指数
++：自增运算（前缀或后缀）
--：自减运算（前缀或后缀）


$((a + 200))      # $a + 200
$(($RANDOM%200))  # 0..199 之间的随机数

(cd somedir; echo "I'm now in $PWD")
pwd # still in first directory

command -V cd
#=> "cd is a function/alias/whatever"

source "${0%/*}/../share/foo.sh"

DIR="${0%/*}"

printf "Hello %s, I'm %s" Sven Olga
#=> "Hello Sven, I'm Olga

printf "1 + 1 = %d" 2
#=> "1 + 1 = 2"

printf "Print a float: %f" 2
#=> "Print a float: 2.000000"

args=("$@")
args+=(foo)
args+=(bar)
echo "${args[@]}"

将参数放入数组中，然后追加

pwd # /home/user/foo
cd bar/
pwd # /home/user/foo/bar
cd -
pwd # /home/user/foo

echo -n "Proceed? [y/n]: "
read ans
echo $ans

read -n 1 ans    # 读取一个字符

git commit && git push
git commit || echo "Commit failed"

set -euo pipefail
IFS=$'\n\t'

更多: Unofficial bash strict mode

cat <<END
hello world
END

stty erase ^h
read  -p  "请输入参数信息"

输入参数时正常使用删除字符操作而不会出现 ^H 字符