bash 脚本 - 使用变量创建目录

Question

我有一个这样的脚本 -

#!/usr/bin/env bash

set -e

volume=$(docker volume inspect volume_name | jq '.[0].Mountpoint')
echo $volume
createdir=$volume/testdir
mkdir -p ${createdir}

但它不会在卷路径中创建任何目录。 echo $volume确实打印了正确的路径 - /var/lib/docker/volumes/volume_name/_data
当我给 mkdir -p /var/lib/docker/volumes/volume_name/_data/testdir .它创造了它。我做错了什么替换？

Answer 1

您的问题是因为您的 jq调用缺少 -r选项开关以输出原始字符串而不是不可用作路径的 JSON 字符串。

见 man jq :

--raw-output / -r:

With this option, if the filter´s result is a string then it will be written directly to standard output rather than being formatted as a JSON string with quotes. This can be useful for making jq filters talk to non-JSON-based systems.

此外，为了防止路径分词，请始终在变量的扩展周围添加双引号。

我详细说明了代码注释中双引号是可选的或强制的情况；尽管有疑问，添加双引号是安全的，但以下特殊情况除外:

明确期望的分词或模式匹配。

作为 RegEx 模式的变量扩展。

这是您的修复代码:

#!/usr/bin/env bash

# Expansion of sub-shell output does not need double quotes,
# because it is a simple variable assignment.
# It would be mandatory if the output was an argument to a command.
volume=$(docker volume inspect volume_name | jq -r '.[0].Mountpoint')

# Here double quotes are fancy optional but a good practice anyway.
# If not present and volume contained a globbing pattern,
# it would be expanded. It would also generate a path check access
# to the file-system. Better be safe with double quotes.
echo "$volume"

# Here double quotes are optional because it is an assignment and not
# an argument to a command.
createdir=$volume/testdir

# Here double quotes are mandatory,
# as the variable is an argument to the mkdir command.
mkdir -p -- "$createdir"