在 Bash 中从文本文件创建数组
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Creating an array from a text file in Bash
提问by user2856414
A script takes a URL, parses it for the required fields, and redirects its output to be saved in a file, file.txt. The output is saved on a new line each time a field has been found.
脚本获取一个 URL，将其解析为所需的字段，并将其输出重定向到一个文件file.txt 中。每次找到字段时，输出都会保存在新行上。
file.txt
文件.txt
A Cat
A Dog
A Mouse
etc...
I want to take file.txtand create an array from it in a new script, where every line gets to be its own string variable in the array. So far I have tried:
我想file.txt在一个新脚本中从中获取并创建一个数组，其中每一行都成为数组中自己的字符串变量。到目前为止，我已经尝试过：
#!/bin/bash
filename=file.txt
declare -a myArray
myArray=(`cat "$filename"`)
for (( i = 0 ; i < 9 ; i++))
do
echo "Element [$i]: ${myArray[$i]}"
done
When I run this script, whitespace results in words getting split and instead of getting
当我运行这个脚本时，空格会导致单词被拆分而不是
Desired output
期望输出
Element [0]: A Cat
Element [1]: A Dog
etc...
I end up getting this:
我最终得到这个：
Actual output
实际产量
Element [0]: A
Element [1]: Cat
Element [2]: A
Element [3]: Dog
etc...
How can I adjust the loop below such that the entire string on each line will correspond one-to-one with each variable in the array?
如何调整下面的循环，使每行的整个字符串与数组中的每个变量一一对应？
回答by glenn Hymanman
Use the mapfilecommand:
使用mapfile命令：
mapfile -t myArray < file.txt
The error is using for-- the idiomatic way to loop over linesof a file is:
错误正在使用for- 循环文件行的惯用方法是：
while IFS= read -r line; do echo ">>$line<<"; done < file.txt
See BashFAQ/005for more details.
有关更多详细信息，请参阅BashFAQ/005。
回答by codeforester
mapfileand readarray(which are synonymous) are available in Bash version 4 and above. If you have an older version of Bash, you can use a loop to read the file into an array:
mapfile和readarray（它们是同义词）在 Bash 版本 4 及更高版本中可用。如果您有旧版本的 Bash，您可以使用循环将文件读入数组：
arr=()
while IFS= read -r line; do
arr+=("$line")
done < file
In case the file has an incomplete (missing newline) last line, you could use this alternative:
如果文件的最后一行不完整（缺少换行符），您可以使用以下替代方法：
arr=()
while IFS= read -r line || [[ "$line" ]]; do
arr+=("$line")
done < file
Related:
有关的：
回答by Jahid
You can do this too:
你也可以这样做：
oldIFS="$IFS"
IFS=$'\n' arr=($(<file))
IFS="$oldIFS"
echo "${arr[1]}" # It will print `A Dog`.
Note:
笔记：
Filename expansion still occurs. For example, if there's a line with a literal *it will expand to all the files in current folder. So use it only if your file is free of this kind of scenario.
文件名扩展仍然发生。例如，如果有一行带有文字*，它将扩展到当前文件夹中的所有文件。因此，仅当您的文件没有这种情况时才使用它。
回答by Prateek Joshi
You can simply read each line from the file and assign it to an array.
您可以简单地从文件中读取每一行并将其分配给一个数组。
#!/bin/bash
i=0
while read line
do
arr[$i]="$line"
i=$((i+1))
done < file.txt
回答by Cameron Lowell Palmer
Use mapfile or read -a
使用 mapfile 或 read -a
Always check your code using shellcheck. It will often give you the correct answer. In this case SC2207covers reading a file that either has space separated or newline separated values into an array.
始终使用shellcheck检查您的代码。它通常会给你正确的答案。在这种情况下，SC2207涵盖将具有空格分隔或换行分隔值的文件读取到数组中。
Don't do this
不要这样做
array=( $(mycommand) )
Files with values separated by newlines
值由换行符分隔的文件
mapfile -t array < <(mycommand)
Files with values separated by spaces
值以空格分隔的文件
IFS=" " read -r -a array <<< "$(mycommand)"
The shellcheck page will give you the rationale why this is considered best practice.
shellcheck 页面将为您提供为什么这被认为是最佳实践的基本原理。
回答by dosentmatter
This answersays to use
这个答案说使用
mapfile -t myArray < file.txt
I made a shimfor mapfileif you want to use mapfileon bash < 4.x for whatever reason. It uses the existing mapfilecommand if you are on bash >= 4.x
我做了一个垫片的mapfile，如果你想使用mapfile上的bash <4.x版无论出于何种原因。mapfile如果您使用 bash >= 4.x，它会使用现有命令
Currently, only options -dand -twork. But that should be enough for that command above. I've only tested on macOS. On macOS Sierra 10.12.6, the system bash is 3.2.57(1)-release. So the shim can come in handy. You can also just update your bash with homebrew, build bash yourself, etc.
目前，只有选择-d和-t工作。但这对于上面的命令应该足够了。我只在 macOS 上测试过。在 macOS Sierra 10.12.6 上，系统 bash 是3.2.57(1)-release. 所以垫片可以派上用场。您也可以使用自制软件更新您的 bash，自己构建 bash 等。
It uses this techniqueto set variables up one call stack.
它使用这种技术在一个调用堆栈中设置变量。
