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[root@00 ~]# set -- hello my  "linux shell"
[root@00 ~]# echo $#
3
[root@00 ~]# echo $1
hello
[root@00 ~]# echo $2
my
[root@00 ~]# echo $3
linux shell
[root@00 ~]# for i in "$@"; do echo $i;done
hello
my
linux shell
[root@00 ~]# for i in "$*"; do echo $i;done
hello my linux shell

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[root@00 ~]#  read -p "hello bash :" num1 num2  # " 和变量之间需要一个空格
hello bash : hello_1 hello_2
[root@00 ~]#  echo $num1 $num2
hello_1 hello_2

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<函数名>(){
    ...
    return n
}

function <函数名>(){
    ...
    return n
}

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case $VAR in
    "1"|a) echo 1
    ;;
    2|3) echo 2 or 3
    ;;
    *) echo default
    ;;
esac

if [ $VAR == $VAR ]; then
    ...
fi

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# 满足条件进入(先判断,在执行)
while True ; do
    ...
done
# 先执行一次,在判断
until True ; do
    ...
done

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# 示例1(文件最后一行内容需要换行符,否则将无法读取)
exec < file
while read line; do
    echo $line
done

# 示例2 (文件最后一行内容需要换行符,否则将无法读取)
cat FILE | while read line ; do
    echo $line
done

# 示例3,此方法根据评测据说效率最高 (文件最后一行内容需要换行符,否则将无法读取)
while read line ; do
    ...
done < FILE

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# set shuttle list
PS3="请选择要操作的编号 : "

select shuttle in columbia endeavour challenger discovery atlantis enterprise pathfinder; do
    echo "$REPLY. $shuttle selected"
done

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    # foreach
    for i in <...> ; do
        ...
    done
    # for
    for ((<..>;<..>; <..> )); do
        ...
    done

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for i in {1..100}; do
    echo $i
done

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

# echo {1..100}+ |sed 's#\+$##g'|bc

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#!/bin/bash
for i in {1..20} ; do
    if [ $i -gt 10 ]; then
        set -x              # <<====== 分段调试开始
        echo "i>20: $i"
        set +x              # <<====== 分段调试结束
    else
        echo "i<=10: $i"
    fi
done

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[root@00 ~]# set -x             # <<==== 调试启动
[root@00 ~]# for i in 1 2 3 ; do echo $i ; done
+ for i in 1 2 3
+ echo 1
1
+ for i in 1 2 3
+ echo 2
2
+ for i in 1 2 3
+ echo 3
3
[root@00 ~]# set +x             # <<==== 调试结束

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# 临时生效,终端退出失效
[root@00 ~]# trap "" 2  # 设置信号
[root@00 ~]# trap -p    # 打印设置信号
trap -- '' SIGINT
[root@00 ~]#            # << 此时按Ctrl+c  无任何反映
[root@00 ~]# trap 2     # 信号复原
[root@00 ~]# ^C         # 复员后 Ctrl+c
[root@00 ~]# ^C         # 复员后 Ctrl+c

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#!/bin/bash

# 长短选项兼容

# ./scripts.sh -h
# ./scripts.sh -s <values>
# ./scripts.sh --src_dir <values>
# ./scripts.sh -k <values> 
# ./scripts.sh --key_prefix <values>
# ./scripts.sh -b <values>
# ./scripts.sh --bucket <values>
# ./scripts.sh -f <values>
# ./scripts.sh --file_type <values>
# ./scripts.sh --skip_fixed_strings <values>
# ./scripts.sh --skip_file_prefixes <values>
# ./scripts.sh --skip_path_prefixes <values>
# ...

while getopts "hs:k:b:f:-:" opt; do
  case $opt in
    s) SRC_DIR=$OPTARG;;
    k) KEY_PREFIX=$OPTARG;;
    b) BUCKET=$OPTARG;;
    f) FILE_TYPE=$OPTARG;;
    h) usage;;
    -)
      case $OPTARG in
        src_dir) SRC_DIR=$2; shift;;
        key_prefix) KEY_PREFIX=$2; shift;;
        bucket) BUCKET=$2; shift;;
        skip_fixed_strings) SKIP_FIXED_STRINGS=$2; shift;;
        skip_file_prefixes) SKIP_FILE_PREFIXES=$2; shift;;
        skip_path_prefixes) SKIP_PATH_PREFIXES=$2; shift;;
        skip_suffixes) SKIP_SUFFIXES=$2; shift;;
        file_type) FILE_TYPE=$2; shift;;
        ignore_dir) IGNORE_DIR=$2; shift;;
        check_exists) CHECK_EXISTS=$2; shift;;
        check_hash) CHECK_HASH=$2; shift;;
        rescan_local) RESCAN_LOCAL=$2; shift;;
        log_level) LOG_LEVEL=$2; shift;;
        log_file) LOG_FILE=$2; shift;;
        delete_on_success) DELETE_ON_SUCCESS=$2; shift;;
        *) echo "Invalid option: --$OPTARG"; exit 1;;
      esac;;
    :) echo "Option -$OPTARG requires an argument."; exit 1;;
    \?) echo "Invalid option: -$OPTARG"; exit 1;;
  esac
done

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# scripts.sh -h
# scripts.sh -a action
# scripts.sh -a action -n step1 -n step2
# scripts.sh -a action -e "var1=value1,var2=value2"

declare -- ACTIONS=""
declare -- STEPS=""
declare -- ENV_VARS=""

while getopts "ha:n:e:" opt; do
    case $opt in
    h)
        usage
        exit 0
        ;;
    a)
        ACTIONS=$OPTARG
        ;;
    n)
        STEPS+=$OPTARG" "
        ;;
    e)
        ENV_VARS=$OPTARG
        ;;
    :)
        echo "Option -$OPTARG requires an argument." >&2
        usage
        exit 1
        ;;
    \?)
        echo "Invalid option: -$OPTARG" >&2
        usage
        exit 1
        ;;
    esac
done

shift $((OPTIND - 1))

# 将传入的key=value参数转换成环境变量
# 例如: --env key=value
IFS=',' read -ra ENV_ARR <<<"$ENV_VARS"
for var in "${ENV_ARR[@]}"; do
    IFS='=' read -ra VAR_ARR <<<"$var"
    declare -g "${VAR_ARR[0]}=${VAR_ARR[1]}"
done

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# 双冒号 双冒号短参数必须贴近或无参数,长参数必须等号赋值(长参数名可以不用写完)或无参数(注:无参数时变量偏移也是2位)
# 单冒号参数可以贴近也可以不贴近,但参数必选
# f d a 必须接受参数
# s 参数可选
#
ARGS=`getopt -o f:s::d:a: --long filename:,source::,desc:,action:: -- "$@"`
eval set -- "$ARGS"

while true ; do
    case "$1" in
        -f|--filename)
            fileName=$2 ; shift 2 ;;
        -s|--source)
            case "$2" in
                "") sourceDir='.' ; shift 2 ;;
                 *) sourceDir=$2 ; shift 2 ;;
            esac ;;
        -d|--desc)
            descDir=$2 ; shift 2;;
        -a|--action)
            case "$2" in
                "copy"|"move") action=$2 ; shift 2 ;;
                            *) action="copy" ; shift 2 ;;
            esac ;;
        --) shift ; break ;;
        *) echo "Internal error!" ; exit 1 ;;
    esac
done

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# 一般放在 export PATH 之后 
if [ "$(id -u)" -eq 0 ]; then
  echo "Switching to www user..."
  exec runuser -u www -- "$0" "$@"
fi