Replacing $ with \$ in string variable

Question

I my bash script, I have a string variable with a $ sign it, and the it isn't escaped. It looks like this:

x="hello $world"

Obviously, when I echo "$x", the output is hello, since $world is being interpreted as a variable. My goal is to modify the string to be hello \$world. I tried several techniques, listed below. None of them seem to be working:

y="$(echo "$x" | sed 's/\$/z/g')" (outputs hello)

y="$(echo "$x" | sed 's/$/z/g')" (outputs hello z, even though I didn't escape \ in sed)

Even tried Bash's native string replacement through:

y=${x//\$/z} (outputs hello)

I realize that I could easily do any of these if the string weren't stored in a variable, but the way my script works, this string will be stored in a variable first, so I need to figure out how to add the \ after that. I don't care if I create a new copy of the string or edit the same string.

In your second sed command, the $ (quoted from bash) matches end-of-line, as sed works with basic regular expressions. — Toby Speight
– Toby Speight, Commented Dec 21, 2017 at 16:33
How do you store the string in a variable? I you do it like you show it, $world is gone and you can't get it back, as shown in Toby's answer. — Benjamin W.
– Benjamin W., Commented Dec 21, 2017 at 16:38
Contrast your (first) sed command with a single-quoted '$x' like this: y="$(echo '$x' | sed 's/\$/z/g')". This version sets $y to zx. — Toby Speight
– Toby Speight, Commented Dec 21, 2017 at 16:49
@BenjaminW. I am using a command (jq to be specific) that returns a string that has several unescaped $ signs in it. — lebowski
– lebowski, Commented Dec 21, 2017 at 16:56
If you have a string str containing an unescaped $, like hello $world (and it shows up exactly like that when you issue declare -p str), doing echo "$str" will not try to expand the variable name. Can you show your actual assignment? — Benjamin W.
– Benjamin W., Commented Dec 21, 2017 at 17:10

Toby Speight · Accepted Answer · 2017-12-21 16:32:02Z

4

The assignment (with $world empty or undefined) is the same as writing

x="hello "

Nothing you do to $x will see a $ in there, unless you add it from outside.

Perhaps you meant instead:

x='hello $world'

answered Dec 21, 2017 at 16:32

Toby Speight

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anubhava · Accepted Answer · 2017-12-21 16:31:49Z

3

You can use BASH:

x='hello $world'
echo "${x//\$/\\$}"

hello \$world

answered Dec 21, 2017 at 16:31

anubhava

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2 Comments

Toby Speight Over a year ago

The question has x="hello $world", not x='hello $world' (hence the problem - there's no $ in $x).

anubhava Over a year ago

As you already know double quotes will cause variable expansion so we need to use single quote.

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