How to grep for the dollar symbol ($)?
LinuxUnixGrepLinux Problem Overview
% 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 $$$ and I expect the result to be
% cat temp | grep <what should go here?>
$$$ hello1
hello5 $$$
%
To differentiate, I have marked the prompt as %.
- What is the problem here?
- What should the grep string be?
Linux Solutions
Solution 1 - Linux
The problem is that the shell expands variable names inside double-quoted strings. So for "$$$" it tries to read a variable name starting with the first $.
In single quotes, on the other hand, variables are not expanded. Therefore, '$$$' would work – if it were not for the fact that $ is a special character in regular expressions denoting the line ending. So it needs to be escaped: '\$\$\$'.
Solution 2 - Linux
When you use double quotes " or none use double \: "\\\$\\\$\\\$"
cat t | grep \\\$\\\$\\\$
if you use in single quotes ' you may use:
cat t | grep '\$\$\$'
Solution 3 - Linux
$ grep '\$\$\$' temp
$$$ hello1
hello5 $$$
There's a superflous 'cat' in your command.
Solution 4 - Linux
Works for me:
user@host:~$ cat temp | grep '\$\$\$'
$$$ hello1
hello5 $$$
user@host:~$
Solution 5 - Linux
How about ^.*[$]{3}.*$