如何用命令输出填充bash关联数组? [英] How do I populate a bash associative array with command output?

问题描述

我正在尝试使用命令的输出填充关联数组.我可以不用以下命令来做到这一点:

I'm trying to populate an associative array with the output of a command. I can do it without a command as:

$ declare -A x=( [first]=foo [second]=bar )
$ echo "${x[first]}, ${x[second]}"
foo, bar

并且我可以使用以下命令填充非关联数组:

and I can populate a non-associative array with command output as:

$ declare y=( $(echo 'foo bar') )
$ echo "${y[0]}, ${y[1]}"
foo, bar

但是当我尝试基于以上两种方法创建一条语句，该语句将通过命令填充关联数组时，我收到以下错误消息:

but when I try to build on both of the above to create a statement that will populate an associative array from a command, I get the following error message:

$ declare -A z=( $(echo '[first]=foo [second]=bar') )
-bash: z: $(echo '[first]=foo [second]=bar'): must use subscript when assigning associative array

为什么我会收到该错误消息?用命令的输出填充关联数组的正确语法是什么?我试图避免对

Why am I getting that error message and what is the correct syntax to populate an associative array with the output of a command? I am trying to avoid using eval for the usual reasons, do not want to use a temp file, and of course echo is just being used as an example of a command that produces the effect in question, the real command will be more complicated.

因此，基于以下几个答案，看来这只是我的报价所引起的问题:

So, based on a couple of the answers below, it looks like it was just my quoting that was a problem:

$ declare -A z="( $(echo '[first]=foo [second]=bar') )"
$ echo "${z[first]}, ${z[second]}"
foo, bar

，并且索引和值中带有空格:

and with spaces in the indices and values:

$ declare -A z="( $(echo '[first field]="foo with space" [second]="space bar"') )"
$ echo "${z[first field]}, ${z[second]}"
foo with space, space bar

---

针对评论中关于为什么需要引号的问题进行编辑(

---

EDIT in response to a question in the comments about why the quotes are necessary (How do I populate a bash associative array with command output?) - I don't exactly know but maybe someone else can explain using the results of this script as reference (not expecting the specified indices to be used in the indexed arrays, they're just part of the strings being populated as the array values):

$ cat tst.sh
#!/bin/env bash

set -x

printf 'Indexed, no quotes\n'
declare -a w=( $(echo '[first]=foo [second]=bar') )
declare -p w

printf '\n---\n'

printf 'Indexed, with quotes\n'
declare -a x="( $(echo '[first]=foo [second]=bar') )"
declare -p x

printf '\n---\n'

printf 'Associative, no quotes\n'
declare -A y="( $(echo '[first]=foo [second]=bar') )"
declare -p y

printf '\n---\n'

printf 'Associative, with quotes\n'
declare -A z=( $(echo '[first]=foo [second]=bar') )
declare -p z

.

$ ./tst.sh
+ printf 'Indexed, no quotes\n'
Indexed, no quotes
+ w=($(echo '[first]=foo [second]=bar'))
++ echo '[first]=foo [second]=bar'
+ declare -a w
+ declare -p w
declare -a w=([0]="[first]=foo" [1]="[second]=bar")
+ printf '\n---\n'

---
+ printf 'Indexed, with quotes\n'
Indexed, with quotes
++ echo '[first]=foo [second]=bar'
+ declare -a 'x=( [first]=foo [second]=bar )'
+ declare -p x
declare -a x=([0]="bar")
+ printf '\n---\n'

---
+ printf 'Associative, no quotes\n'
Associative, no quotes
++ echo '[first]=foo [second]=bar'
+ declare -A 'y=( [first]=foo [second]=bar )'
+ declare -p y
declare -A y=([second]="bar" [first]="foo" )
+ printf '\n---\n'

---
+ printf 'Associative, with quotes\n'
Associative, with quotes
+ z=($(echo '[first]=foo [second]=bar'))
./tst.sh: line 24: z: $(echo '[first]=foo [second]=bar'): must use subscript when assigning associative array
+ declare -A z
+ declare -p z
declare -A z=()

推荐答案

这是传统的while循环方法，用于从命令的输出填充关联数组:

Here is a traditional while loop approach to populate an associative array from a command's output:

while IFS= read -r; do
   declare -A z+="( $REPLY )"
done < <(printf '[first]=foo [second]=bar\n[third]=baz\n')

# check output
$> echo "${z[first]}, ${z[second]}, ${z[third]}"
foo, bar, baz

# or declare -p
$> declare -p z
declare -A z='([third]="baz" [second]="bar" [first]="foo" )'

编辑:您最初的尝试也可以使用正确的引号:

Your original attempt will also work with proper quotes:

$> unset z

$> declare -A z="( $(echo '[first]=foo [second]=bar') )"

$> declare -p z
declare -A z='([second]="bar" [first]="foo" )'

这篇关于如何用命令输出填充bash关联数组?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！