How to grep for the dollar symbol ($)?

Question

% cat temp
$$$ hello1
$$  hello2
    hello3
##  hello4
    hello5 $$$
% cat temp | grep \"$$$\"
Illegal variable name.
% cat temp | grep \"\\$\\$\\$\"
Variable name          


        

Answer 1

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: '\$\$\$'.