bash 如何一次性将文件内容读入变量？
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How to read the file content into a variable in one go?
提问by Shengjie
In Java, if you know for certain a file is very small, you can use readBytes()method to read the content in one go instead of read it line by line or using buffer.
在Java中，如果你确定一个文件很小，你可以使用readBytes()方法一次读取内容，而不是逐行读取或使用缓冲区。
Just wondering in shell script, I know we can do something like:
只是想知道在 shell 脚本中，我知道我们可以执行以下操作：
while read line
do
echo $line
LINE = $line
done < "test.file"
echo $LINE
If my test.file is like:
如果我的 test.file 是这样的：
testline1
testline2
testline3
This only gives me the last line to $LINE. $LINEcontains "testline3".
这只会给我最后一行$LINE。$LINE包含“testline3”。
My question is: How can I read the whole file with multiple lines into one single variable,so I can get $LINE="testline1\ntestline2\ntestline3"?
我的问题是：如何将包含多行的整个文件读入一个变量中，以便获得$LINE="testline1\ntestline2\ntestline3"？
回答by Paused until further notice.
Process the lines inside the loop instead of after it. If you really need the file in a variable:
处理循环内的行而不是在循环之后。如果您确实需要变量中的文件：
var=$(<file)
回答by Stephen Niedzielski
Another alternative is to use the nice mapfile builtin:
另一种选择是使用漂亮的 mapfile 内置：
mapfile < test.file
echo "${MAPFILE[@]}"
回答by Mark Reed
As another option, you can build an array of lines. If you're running bash 4+, you can use the mapfilebuiltin:
作为另一种选择，您可以构建一系列行。如果您运行的是 bash 4+，则可以使用mapfile内置命令：
mapfile -t lines <test.file
If you want the lines to be output as well as stored you could do something like this:
如果您希望输出和存储行，您可以执行以下操作：
mapfile -t lines < <(tee /dev/tty <test.file)
Then "${lines[0]}"will be the first line of the file, "${lines[1]}"the second, and so on. ${#lines[@]}will be the number of lines; "${lines[@]}"will be the whole array, while "${lines[*]}"will be the lines joined together with spaces into one big string.
然后"${lines[0]}"将是文件的第一行，"${lines[1]}"第二行，依此类推。${#lines[@]}将是行数；"${lines[@]}"将是整个数组，而"${lines[*]}"行将用空格连接成一个大字符串。
For older versions of bash, you can build the array manually:
对于较旧版本的 bash，您可以手动构建数组：
lines=()
while IFS= read -r line
do
printf '%s\n' "$line"
lines+=("$line")
done < test.file
