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hello.sh

#!/bin/bash VAR="world" echo "Hello $VAR!" # => Hello world! 

执行脚本

$ bash hello.sh 

变量

NAME="John" echo ${NAME} # => John (变量) echo $NAME # => John (变量) echo "$NAME" # => John (变量) echo '$NAME' # => $NAME (字符串原样输出) echo "${NAME}!" # => John! (变量) NAME = "John" # => Error (注意不能有空格) 

注释

# 这是一个内联 Bash 注释。 : ' 这是一个 非常整洁的 bash 注释 ' 

多行注释使用 :’ 打开和 ‘ 关闭

参数

见：特殊参数

函数

get_name() { echo "John" } echo "You are $(get_name)" 

见：函数

条件句

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

见：条件句

大括号扩展

echo {A,B}.js 

见：大括号扩展

Shell 执行

# => I'm in /当前/的/路径 echo "I'm in $(PWD)" # Same as: echo "I'm in `pwd`" 

见：命令替换

Bash 参数扩展

语法

子字符串

Length

默认值

替代 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 (extension) echo ${STR##*/} # foo.cpp (basepath) echo ${STR#*/} # path/to/foo.cpp echo ${STR##*/} # foo.cpp echo ${STR/foo/bar} # /path/to/bar.cpp 

切片 Slicing

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 

见：参数扩展

基本路径和目录路径

SRC="/path/to/foo.cpp" 

BASEPATH=${SRC##*/} echo $BASEPATH # => "foo.cpp" DIRPATH=${SRC%$BASEPATH} echo $DIRPATH # => "/path/to/" 

Transform

STR="HELLO WORLD!" echo ${STR,} # => hELLO WORLD! echo ${STR,,} # => hello world! STR="hello world!" echo ${STR^} # => Hello world! echo ${STR^^} # => HELLO WORLD! ARR=(hello World) echo "${ARR[@],}" # => hello world echo "${ARR[@]^}" # => Hello World 

Bash 数组

定义数组

Fruits=('Apple' 'Banana' 'Orange') Fruits[0]="Apple" 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) # 附加 => 1 2 3 4 5 

索引

迭代 Iteration

Fruits=('Apple' 'Banana' 'Orange') for e in "${Fruits[@]}"; do echo $e done 

With index

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

操作

Fruits=("${Fruits[@]}" "Watermelon") # 添加 Fruits+=('Watermelon') # 也是添加 Fruits=( ${Fruits[@]/Ap*/} ) # 通过正则表达式匹配删除 unset Fruits[2] # 删除一项 Fruits=("${Fruits[@]}") # 复制 Fruits=("${Fruits[@]}" "${Veggies[@]}") # 连接 lines=(`cat "logfile"`) # 从文件中读取 

数组作为参数

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

Bash 字典

定义

declare -A sounds 

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

使用字典

echo ${sounds[dog]} # Dog's sound echo ${sounds[@]} # All values echo ${!sounds[@]} # All keys echo ${#sounds[@]} # Number of elements unset sounds[dog] # Delete dog 

迭代

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

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

Bash 条件句

整数条件

字符串条件

例子

字符串

if [[ -z "$string" ]]; then echo "String is empty" elif [[ -n "$string" ]]; then echo "String is not empty" else echo "This never happens" fi 

组合

if [[ X && Y ]]; then ... fi 

相等

if [[ "$A" == "$B" ]]; then ... fi 

正则表达式

if [[ '1. abc' =~ ([a-z]+) ]]; then echo ${BASH_REMATCH[1]} fi 

小于

if (( $a < $b )); then echo "$a is smaller than $b" fi 

存在

if [[ -e "file.txt" ]]; then echo "file exists" fi 

文件条件

更多条件

逻辑和，或

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

Bash 循环

基本 for 循环

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

类似 C 的 for 循环

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

范围

for i in {1..5}; do echo "Welcome $i" done 

步长

for i in {5..50..5}; do echo "Welcome $i" done 

自动递增

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

自动递减

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

Continue

for number in $(seq 1 3); do if [[ $number == 2 ]]; then continue; fi echo "$number" done 

Break

for number in $(seq 1 3); do if [[ $number == 2 ]]; then # Skip entire rest of loop. break; fi # This will only print 1 echo "$number" done 

Until

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

死循环

while true; do # here is some code. done 

死循环（简写）

while :; do # here is some code. done 

读取文件的每一行

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

Bash 函数

定义函数

myfunc() { echo "hello $1" } 

# 同上（替代语法） function myfunc() { echo "hello $1" } 

myfunc "John" 

返回值

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

result="$(myfunc)" 

抛出错误

myfunc() { return 1 } 

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

Bash 选项

选项

# 避免覆盖文件 # (echo "hi" > foo) set -o noclobber # 用于出错时退出 # 避免级联错误 set -o errexit # 揭示隐藏的失败 set -o pipefail # 公开未设置的变量 set -o nounset 

全局选项

# 不匹配的 glob 被删除 # ('*.foo' => '') shopt -s nullglob # 不匹配的 glob 抛出错误 shopt -s failglob # 不区分大小写的球体 shopt -s nocaseglob # 通配符匹配点文件 # ("*.sh" => ".foo.sh") shopt -s dotglob # 允许 ** 进行递归匹配 # ('lib/**/*.rb' => 'lib/a/b/c.rb') shopt -s globstar 

Bash 历史

命令

表达式

操作

!! 和 !$ 可以替换为任何有效的扩展。

切片 Slices

!! 可以替换为任何有效的扩展，即 !cat、!-2、!42 等。

杂项

数值计算

$((a + 200)) # Add 200 to $a 

$(($RANDOM%200)) # Random number 0..199 

子 shell

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

检查命令

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

重定向

python hello.py > output.txt # 标准输出到（文件） python hello.py >> output.txt # 标准输出到（文件），追加 python hello.py 2> error.log # 标准错误到（文件） python hello.py 2>&1 # 标准错误到标准输出 python hello.py 2>/dev/null # 标准错误到（空null） python hello.py &>/dev/null # 标准输出和标准错误到（空null） 

python hello.py < foo.txt # 将 foo.txt 提供给 python 的标准输入 

来源相对

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

脚本目录

DIR="${0%/*}" 

Case/switch

case "$1" in start | up) vagrant up ;; *) echo "Usage: $0 {start|stop|ssh}" ;; esac 

陷阱错误

trap 'echo Error at about $LINENO' ERR 

或者

traperr() { echo "ERROR: ${BASH_SOURCE[1]} at about ${BASH_LINENO[0]}" } set -o errtrace trap traperr ERR 

printf

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" 

获取选项

while [[ "$1" =~ ^- && ! "$1" == "--" ]]; do case $1 in -V | --version ) echo $version exit ;; -s | --string ) shift; string=$1 ;; -f | --flag ) flag=1 ;; esac; shift; done if [[ "$1" == '--' ]]; then shift; fi 

检查命令的结果

if ping -c 1 google.com; then echo "看来您的互联网连接正常" fi 

特殊变量

见特殊参数。

grep 检查

if grep -q 'foo' ~/.bash_history; then echo "您过去似乎输入过“foo”" fi 

反斜杠转义

• !
• “
• #
• &
• ‘
• (
• )
• ,
• ;
• <
• >
• [
• |
• \
• ]
• ^
• {
• }
• `
• $
• *
• ?

使用 \ 转义这些特殊字符

Heredoc

cat <<END hello world END 

转到上一个目录

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

读取输入

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

read -n 1 ans # 只有一个字符 

条件执行

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

严格模式

set -euo pipefail IFS=#39;\n\t' 

参见：非官方 bash 严格模式

可选参数

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

将参数放入数组中，然后追加