Linux 如何grep美元符号（$）？
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How to grep for the dollar symbol ($)?
提问by Lazer
% cat temp
$$$ hello1
$$ hello2
hello3
## hello4
hello5 $$$
% cat temp | grep "$$$"
Illegal variable name.
% cat temp | grep "$$$"
Variable name must contain alphanumeric characters.
%
I want to grep for $$$and I expect the result to be
我想 grep for$$$并且我希望结果是
% cat temp | grep <what should go here?>
$$$ hello1
hello5 $$$
%
To differentiate, I have marked the prompt as %.
为了区分，我将提示标记为%.
- What is the problem here?
- What should the grep stringbe?
- 这里有什么问题？
- 应该采取什么grep的字符串是什么？
采纳答案by Konrad Rudolph
The problem is that the shell expands variable names inside double-quoted strings. So for "$$$"it tries to read a variable name starting with the first $.
问题在于 shell 在双引号字符串中扩展变量名。因此，"$$$"它尝试读取以第一个开头的变量名称$。
In single quotes, on the other hand, variables are not expanded. Therefore, '$$$'wouldwork –?if it were not for the fact that $is a special character in regular expressions denoting the line ending. So it needs to be escaped: '\$\$\$'.
另一方面，在单引号中，变量不会被扩展。因此，如果不是正则表达式中表示行尾的特殊字符，它'$$$'会起作用$。所以它需要被转义：'\$\$\$'.
回答by F.P
How about ^.*[$]{3}.*$
怎么样 ^.*[$]{3}.*$
回答by tdammers
Works for me:
对我有用：
user@host:~$ cat temp | grep '$$$'
$$$ hello1
hello5 $$$
user@host:~$
回答by Gadolin
When you use double quotes "or none use double\: "\\\$\\\$\\\$"
当您使用双引号"或不使用双引号时\: "\\\$\\\$\\\$"
cat t | grep \$\$\$
if you use in single quotes ' you may use:
如果您在单引号中使用 ' 您可以使用：
cat t | grep '$$$'
回答by jowi
$ grep '$$$' temp
$$$ hello1
hello5 $$$
There's a superflous 'cat' in your command.
你的命令中有一个多余的“猫”。
回答by haykp
Same issue with this command
这个命令有同样的问题
complete -W "\`grep -oE '^[a-zA-Z0-9_.-]+:([^=]|$)' Makefile \`"
Illegal variable name.
非法的变量名。
