协议缓冲区与平坦缓冲区(Protocol Buffers vs Flat Buffers [closed])

 您想使用“先前在脚本中定义的变量”。 以下是变量： 
 
file="path/to/input/file"
var="ssh_param"
msg="#New path defined"
new="/etc/ssh/file"
 
 以下是使用这些变量的命令： 
 
lineno=$(grep -n "$var" "$file" | tail -n1 | sed 's/:.*//')
if [ "$lineno" ]
then
    sed -i -r "$lineno s|#?(.*)|#\1\n$msg\n$var $new|" "$file"
else
    sed -i -r "$ s|$|\n$msg\n$var $new|" "$file"
fi
 
 笔记： 
 
 
 
 从您的示例中可以看出，变量名称可能在脚本中多次出现，但只有最后一个名称未被注释。 我们在这里使用它来简化代码。 脚本中变量最后一次出现的行号可从以下位置找到： 
lineno=$(grep -n "$var" "$file" | tail -n1 | sed 's/:.*//')
 grep -n部分查找出现变量名的行号列表。 tail -n1只返回最后一行。 sed命令从输出中删除除行号以外的所有行号。 
 
 
 替换是通过以下命令完成的： 
sed -i -r "$lineno s|#?(.*)|#\1\n$msg\n$var $new|" "$file"`
 这使用sed的能力来操作特定的行号。 该行由三行代替：第一行是现有行的副本，但是已注释，第二行是消息，第三行是变量的新定义。 
 
 
 如果变量当前不在文件中，则lineno为空。 在这种情况下，我们希望将新行添加到文件的末尾。 这是通过类似但更简单的sed命令完成的： 
sed -i -r "$ s|$|\n$msg\n$var $new|" "$file"
 
 
 第一个$告诉sed仅在最后一行操作。 第二个$出现在substitute命令中，表示该行的结束。 您的消息和新变量定义将被追加。 
 
 例 
 
 以此为输入： 
 
#ssh_param dasfda
ssh_param /path/to/file
 
 上面的代码用以下代码替换文件： 
 
#ssh_param dasfda
#ssh_param /path/to/file
#New path defined
ssh_param /etc/ssh/file
 
 （如果你想要空行来分隔，只需在sed输出表达式中添加一些\n 。） 

You wanted to use "variables defined earlier in the script." Here are the variables:
 
file="path/to/input/file"
var="ssh_param"
msg="#New path defined"
new="/etc/ssh/file"
 
Here are the commands which use those variables:
 
lineno=$(grep -n "$var" "$file" | tail -n1 | sed 's/:.*//')
if [ "$lineno" ]
then
    sed -i -r "$lineno s|#?(.*)|#\1\n$msg\n$var $new|" "$file"
else
    sed -i -r "$ s|$|\n$msg\n$var $new|" "$file"
fi
 
Notes:
 
 
 
It appears from your examples that the variable name may occur multiple times in the script but only the last one is uncommented. We use that here to simplify the code. The line number of the last appearance of the variable in the script is found from:
 
lineno=$(grep -n "$var" "$file" | tail -n1 | sed 's/:.*//')
 
The grep -n part finds a list of line numbers on which the variable name occurs. tail -n1 returns only the last such line. The sed command removes all but the line number from the output.
 
 
The substitution is done by this command:
 
sed -i -r "$lineno s|#?(.*)|#\1\n$msg\n$var $new|" "$file"`
 
This uses sed's ability to operate on a particular line number. That line is substituted by three lines: the first is a copy of the existing line but commented, the second is the message, and the third is the new definition of the variable.
 
 
If the variable is not currently in the file, then lineno is empty. In this case, we want to add the new lines to the end of the file. This is done via a similar but simpler sed command:
 
sed -i -r "$ s|$|\n$msg\n$var $new|" "$file"
 
 
The first $ tells sed to operate only on the last line. The second$ appears in the substitute command where it signifies the end of that line. Your message and new variable definition are appended.
 
Example
 
With this as the input:
 
#ssh_param dasfda
ssh_param /path/to/file
 
The above code replaces the file with:
 
#ssh_param dasfda
#ssh_param /path/to/file
#New path defined
ssh_param /etc/ssh/file
 
(If you want blank lines to space things out, just add some \n to the sed output expression.)