bash 脚本将内容写入文件。文件内容需要 bash 变量。怎么做？
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bash script to write content into file. File content requires bash variables. How to do that?
提问by Kim Stacks
The following is a piece of content my bash script will write into the nginx configuration file.
下面是我的bash脚本将写入nginx配置文件的一段内容。
WEBAPP=example.com
APPFOLDER=abcapp
CONFFILENAME=abc.conf
read -r -d '' FILECONTENT <<'ENDFILECONTENT'
server {
listen 80;
client_max_body_size 2M;
server_name $WEBAPP;
root /var/virtual/stage.$WEBAPP/current/src/$APPFOLDER/webroot;
}
ENDFILECONTENT
echo "$FILECONTENT" > /etc/nginx/sites-available/$CONFFILENAME
The code works successfully to write the content inside /etc/nginx/sites-available/abc.conf.
该代码成功地将内容写入其中/etc/nginx/sites-available/abc.conf。
However, I have two bash variables in $WEBAPPand $APPFOLDER. They are manifested exactly like that inside the file instead of example.comand abcappwhich is what I intended.
但是，我在$WEBAPP和 中有两个 bash 变量$APPFOLDER。他们表现完全一样的文件，而不是内部example.com和abcapp这正是我打算。
How do I make the script work as intended?
如何使脚本按预期工作？
回答by rici
bash allows newlines in quoted strings. It does parameter replacement (that is, $FOOgets replaced with the value of FOO) inside double-quoted strings ("$FOO") but not inside single-quoted strings ('$FOO').
bash 允许在带引号的字符串中换行。它在双引号字符串 ( ) 内而不是在单引号字符串 ( )内进行参数替换（即被$FOO替换为 的值）。FOO"$FOO"'$FOO'
So you could just do this:
所以你可以这样做：
FILECONTENT="server {
listen 80;
client_max_body_size 2M;
server_name $WEBAPP;
root /var/virtual/stage.$WEBAPP/current/src/$APPFOLDER/webroot;
}"
echo "$FILECONTENT" > /etc/nginx/sites-available/$CONFFILENAME
You don't really need the FILECONTENTparameter, since you could just copy directly to the file:
您实际上并不需要该FILECONTENT参数，因为您可以直接复制到文件中：
cat >/etc/nginx/sites-available/$CONFFILENAME <<ENDOFCONTENT
server {
listen 80;
client_max_body_size 2M;
server_name $WEBAPP;
root /var/virtual/stage.$WEBAPP/current/src/$APPFOLDER/webroot;
}
ENDOFCONTENT
In the second example, using <<ENDOFCONTENTindicates that the $VARs should be replaced with their values <<'ENDOFCONTENT'would prevent the parameter replacement.
在第二个示例中， using<<ENDOFCONTENT指示$VAR应该用它们的值替换 s<<'ENDOFCONTENT'将阻止参数替换。
回答by Jeff Bowman
You're actually deliberately turning off parameter subsitution by enclosing 'ENDFILECONTENT'in quotes. See this excerpt from example 19-7 of the advanced Bash scripting guide on Heredocs, slightly reformatted:
您实际上是通过'ENDFILECONTENT'用引号引起来故意关闭参数替换。请参阅Heredocs上的高级 Bash 脚本指南的示例 19-7 的摘录，稍微重新格式化：
# No parameter substitution when the "limit string" is quoted or escaped.
# Either of the following at the head of the here document would have
# the same effect.
#
# cat <<"Endofmessage"
# cat <<\Endofmessage
Remove the single quotes around 'ENDFILECONTENT'and BASH will replace the variables as expected.
删除周围的单引号'ENDFILECONTENT'，BASH 将按预期替换变量。
