BASH - Replace substring “$$” with substring “$$$”

Question

Essentially what I am trying to do is take a string with a bunch of text and if it has a substring of "$$" to replace it with a substring of "$$$"

ex:

string="abcde\$\$fghi"
# Modify string
echo $string 
# ^ should give "abcde$$$fghi"

I have been at this for like 2 hours now and it seems like a very simple thing, so if anyone could provide some help then I would greatly appreciate it. Thanks!

EDIT: Changed original string in the question from "abcde$$fghi" to "abcde\\$\\$fghi"

Answer 1

$$ is a special variable in the shell, it contains the ID of the current process. The variables are expanded in double quotes, therefore string does not contain $$ but a number (the PID of shell) instead.
Enclose the string in apostrophes (single quotes) to get $$ inside it.

The replacement you need can be done in multiple ways. The simplest way (probably) and also the fastest way (for sure) is to use / in the parameter expansion of $string :

echo "${string/'$$'/'$$$'}"

To make it work you have to use the same trick as before: wrap $$ and $$$ in single quotes to prevent the shell replace them with something else. The quotes around the entire expression are needed to preserve the space characters contained by $string , otherwise the line is split to words by whitspaces and and echo outputs these words separated by one space character.

Check it online .

Answer 2

If you quote the string with single quote marks (ie string='abcde$$fghi' ) you can do the replacement with echo "${string/'$$'/'$$$'}"

Edit: this is basically what @axiac said in their comment