Linux常用命令-shift

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命令

shift

描述

移动位置参数,可用于传递多个参数

用法

1
shift [n]

选项

无

注意

如果需要同时指定选项和参数,如-a aa,则需要在case循环里添加shift,$1为选项-a,$2为参数aa
如果只需要指定选项,如-a -b,则只需要在case循环外添加shift即可,$1始终为选项
在case循环中只设置变量,而不要直接执行命令,建议在循环外判断变量值后再执行相应的命令

示例

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# bash脚本中可以通过shift传递多个参数
$ cat a.sh
echo num is $#
echo "all is $*"
while [ $# -gt 0 ]; do
    echo $#
    case $1 in
        -a)
            echo "-a is '$*'"
            echo "-a \$12 is '$1' '$2'"
            # 如果需要同时指定选项和参数,如-a aa,则需要在case循环里添加shift,$1为选项-a,$2为参数aa
            # 如果只需要指定选项,如-a -b,则只需要在case循环外添加shift即可,$1始终为选项
            shift
            ;;
        -b)
            echo "-b is $*"
            echo "-b \$123 is $1 $2 $3"
            # 在case循环中只设置变量,而不要直接执行命令,建议在循环外判断变量值后再执行相应的命令
            #save_log=$1
            #file_path=$2
            shift
            ;;
        -c)
            echo "-c is $*"
            shift
            ;;
        *)
            #echo "* is $*"
            echo help
            # 如果输入的参数无效则退出
            #exit
            ;;
    esac
    shift
done

$ bash a.sh -a aa
num is 2
all is -a aa
2
-a is '-a aa'
-a $12 is '-a' 'aa'

$ bash a.sh -a aa -b bb -c cc
num is 6
all is -a aa -b bb -c cc
6
-a is '-a aa -b bb -c cc'
-a $12 is '-a' 'aa'
4
-b is -b bb -c cc
-b $123 is -b bb -c
2
-c is -c cc

$ bash a.sh -a aa -b bb -c cc -d dd
num is 8
all is -a aa -b bb -c cc -d dd
8
-a is '-a aa -b bb -c cc -d dd'
-a $12 is '-a' 'aa'
6
-b is -b bb -c cc -d dd
-b $123 is -b bb -c
4
-c is -c cc -d dd
2
help
1
help

# 注意两次shift分别为case循环和while循环,参数-d dd只执行了while循环中的shift
$ bash -x a.sh -a aa -b bb -c cc -d dd
+ echo num is 8
num is 8
+ echo 'all is -a aa -b bb -c cc -d dd'
all is -a aa -b bb -c cc -d dd
+ '[' 8 -gt 0 ']'
+ echo 8
8
+ case $1 in
+ echo '-a is '\''-a aa -b bb -c cc -d dd'\'''
-a is '-a aa -b bb -c cc -d dd'
+ echo '-a $12 is '\''-a'\'' '\''aa'\'''
-a $12 is '-a' 'aa'
+ shift
+ shift
+ '[' 6 -gt 0 ']'
+ echo 6
6
+ case $1 in
+ echo '-b is -b bb -c cc -d dd'
-b is -b bb -c cc -d dd
+ echo '-b $123 is -b bb -c'
-b $123 is -b bb -c
+ shift
+ shift
+ '[' 4 -gt 0 ']'
+ echo 4
4
+ case $1 in
+ echo '-c is -c cc -d dd'
-c is -c cc -d dd
+ shift
+ shift
+ '[' 2 -gt 0 ']'
+ echo 2
2
+ case $1 in
+ echo help
help
+ shift
+ '[' 1 -gt 0 ']'
+ echo 1
1
+ case $1 in
+ echo help
help
+ shift
+ '[' 0 -gt 0 ']'


# 需要关闭case循环中的shift
$ bash a.sh -a -b
num is 2
all is -a -b
2
-a $12 is '-a' '-b'
1
-b $12 is -b

# 需要开启case循环中的shift
$ bash a.sh -a aa -b bb 
num is 4
all is -a aa -b bb
4
-a $12 is '-a' 'aa'
2
-b $12 is -b bb

# 示例
mirror=''
DRY_RUN=${DRY_RUN:-}
while [ $# -gt 0 ]; do
    case "$1" in
        --mirror)
            mirror="$2"
            shift
            ;;
        --dry-run)
            DRY_RUN=1
            ;;
        --*)
            echo "Illegal option $1"
            ;;
    esac
    shift
done
case "$mirror" in
    Aliyun)
        DOWNLOAD_URL="https://mirrors.aliyun.com/docker-ce"
        ;;
    AzureChinaCloud)
        DOWNLOAD_URL="https://mirror.azure.cn/docker-ce"
        ;;
esac