sed s command & e flag: `echo '$-' | sed 's/-//e'` gives: `sh: $: command not found`

Question

I'm having a problem with sed, when using its 's' (search and replace command) with its 'e' flag, as in

sed 's/.../.../e'

The problem is that the characters $, (, and ) in the standard input appear to confuse it.

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I first ran into it here and have now boiled it down to this:

echo '$-' | sed 's/x//e'               # works when pattern is NOT matched
$-

echo '$-' | sed 's/-//e'               # fails when pattern is matched: gags on $
sh: $: command not found

echo '-' | sed 's/-//e'                # works when $ isn't present

echo '-(' | sed 's/-//e'               # Also fails when '(' or ')' are found
sh: -c: line 1: syntax error: unexpected end of file

echo '(' | sed 's/-//e'                # But works with this
(

echo '$-' | sed 's/-/echo xx/e'        # also fails
sh: xx: command not found

echo '$-' | sed 's/\(-\)/echo '\1'/e'  # also fails
sh: 1: command not found

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Here's what the GNU manual says:

3.3 The s Command

...

The s command can be followed by zero or more of the following flags:

...

e

This command allows one to pipe input from a shell command into pattern space. If a substitution was made, the command that is found in pattern space is executed and pattern space is replaced with its output. A trailing newline is suppressed; results are undefined if the command to be executed contains a NUL character. This is a GNU sed extension.

---

bash --version
GNU bash, version 5.0.3(1)-release (x86_64-pc-linux-gnu)

sed --version
sed (GNU sed) 4.7
Packaged by Debian

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What am I missing or doing wrong?

Answer 1

Running

echo '$-' | sed 's/-//e'

removes the - from $-, leaving just $, and the result is run as a shell command, because of /e.

The result is the same is if you try to run $ from the command line:

sh: $: command not found

And similarly for all other lines.