Bash scriptingcheatsheet

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#!/usr/bin/env bash
NAME="John"
echo "Hello $NAME!"

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NAME="John"
echo $NAME
echo "$NAME"
echo "${NAME}!"

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NAME="John"
echo "Hi $NAME"  #=> Hi John
echo 'Hi $NAME'  #=> Hi $NAME

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echo "I'm in $(pwd)"
echo "I'm in `pwd`"
# Same

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

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

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

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

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echo {A,B}.js

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name="John"
echo ${name}
echo ${name/J/j}    #=> "john" (substitution)
echo ${name:0:2}    #=> "Jo" (slicing)
echo ${name::2}     #=> "Jo" (slicing)
echo ${name::-1}    #=> "Joh" (slicing)
echo ${name:(-1)}   #=> "n" (slicing from right)
echo ${name:(-2):1} #=> "h" (slicing from right)
echo ${food:-Cake}  #=> $food or "Cake"

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

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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

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STR="Hello world"
echo ${STR:6:5}   # "world"
echo ${STR: -5:5}  # "world"

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SRC="/path/to/foo.cpp"
BASE=${SRC##*/}   #=> "foo.cpp" (basepath)
DIR=${SRC%$BASE}  #=> "/path/to/" (dirpath)

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# Single line comment

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: '
This is a
multi line
comment
'

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STR="HELLO WORLD!"
echo ${STR,}   #=> "hELLO WORLD!" (第一个字母小写)
echo ${STR,,}  #=> "hello world!" (全部)
STR="hello world!"
echo ${STR^}   #=> "Hello world!" (第一个字母大写)
echo ${STR^^}  #=> "HELLO WORLD!" (全部)

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

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

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

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

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

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while true; do
  ···
done

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myfunc() {
    echo "hello $1"
}

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# 效果和上面一样
function myfunc() {
    echo "hello $1"
}

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myfunc "John"

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

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result="$(myfunc)"

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myfunc() {
  return 1
}

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

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

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

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if [[ "$A" == "$B" ]]

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if [[ "A" =~ . ]]

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

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

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

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

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echo ${Fruits[0]}           # 第一个元素
echo ${Fruits[-1]}          # 最后一个元素
echo ${Fruits[@]}           # 全部元素，以空格分隔
echo ${#Fruits[@]}          # 数组元素的数量
echo ${#Fruits}             # 第一个元素的字符串长度
echo ${#Fruits[3]}          # 第N个元素的字符串长
echo ${Fruits[@]:3:2}       # 范围(从第三个开始长度 2)
echo ${!Fruits[@]}          # 所有元素的 Key ，空格分隔

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Fruits=("${Fruits[@]}" "Watermelon")    # Push
Fruits+=('Watermelon')                  # 也是 Push
Fruits=( ${Fruits[@]/Ap*/} )            # 根据正则移除元素
unset Fruits[2]                         # 移除一个元素
Fruits=("${Fruits[@]}")                 # 复制一份
Fruits=("${Fruits[@]}" "${Veggies[@]}") # 连接两个数组
lines=(`cat "logfile"`)                 # 从文件中读取

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for i in "${arrayName[@]}"; do
  echo $i
done

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declare -A sounds

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

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echo ${sounds[dog]} # Key-Value
echo ${sounds[@]}   # 全部的值
echo ${!sounds[@]}  # 全部的键
echo ${#sounds[@]}  # 元素的数量
unset sounds[dog]   # 删除 dog 值

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set -o noclobber  # 阻止你覆盖文件
set -o errexit    # 遇到错误即退出
set -o pipefail   # 显示隐藏的错误
set -o nounset    # 显示未设置的变量

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shopt -s nullglob    # 无匹配时输出空字符串
shopt -s failglob    # 无匹配时弹出错误
shopt -s nocaseglob  # 大小写敏感的 Glob
shopt -s dotglob     # 通配符匹配 .xxx.xx 隐藏文件 ("*.sh" => ".foo.sh")
shopt -s globstar    # 允许递归的匹配('lib/**/*.rb' => 'lib/a/b/c.rb')

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$((a + 200))      # a 加 200

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$(($RANDOM%200))  # 随机数 0..199

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(cd somedir; echo "I'm now in $PWD")
pwd # 还在最开始的目录

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python hello.py > output.txt   # 标准输出至文件
python hello.py >> output.txt  # 标准输出至文件（Append 模式）
python hello.py 2> error.log   # 标准错误输出值文件
python hello.py 2>&1           # 标准错误输出至标准输出中
python hello.py 2>/dev/null    # 不输出标准错误
python hello.py &>/dev/null    # 什么也输出

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python hello.py < foo.txt      # foo.txt 的内容作为标准输入至 Python 脚本中

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

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trap 'echo Error at about $LINENO' ERR

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

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

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

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printf "Hello %s, I'm %s" Sven Olga
#=> "Hello Sven, I'm Olga
printf "1 + 1 = %d" 2
#=> "1 + 1 = 2"
printf "This is how you print a float: %f" 2
#=> "This is how you print a float: 2.000000"

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DIR="${0%/*}"

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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

SH
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cat <<END
hello world
END

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

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read -n 1 ans    # Just one character

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

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if ping -c 1 google.com; then
  echo "It appears you have a working internet connection"
fi

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if grep -q 'foo' ~/.bash_history; then
  echo "You appear to have typed 'foo' in the past"
fi