xargs: command substitution $(...) with pipe doesn't work

Question

I'm trying to write short script, and the following command:

echo "aaa111 bbb111" | xargs -I {} echo {} | sed 's/111/222/g'

returns aaa222 bbb222, which is what I expect.

I expected the next command:

echo "aaa111 bbb111" | xargs -I {} echo $(echo {} | sed 's/111/222/g')

to return the same, but it returns aaa111 bbb111! Why is that?

---

UPD: What I'm trying to achieve:

I have many files like pic30-coff-gcc, pic30-coff-ag, etc, and I need to make a symlink for each file, like pic30-gcc -> pic30-coff-gcc, etc.

So I wrote this:

ls|grep 'coff-'|xargs -I {} ln -s {} $(echo {} | sed 's/coff-//g')

It doesn't work: for each file, it reports that file exists. I checked the command like this:

ls|grep 'coff-'|xargs -I {} echo "ln -s {} $(echo {} | sed 's/coff-//g')"

And yep, the sed part doesn't work:

ln -s pic30-coff-gcc pic30-coff-gcc
ln -s pic30-coff-gcc-4.0.3 pic30-coff-gcc-4.0.3
...

But if I just type

echo "ln -s pic30-coff-gcc $(echo pic30-coff-gcc | sed 's/coff-//g')"

it works:

ln -s pic30-coff-gcc pic30-gcc

Then I've written test command with aaa111, and it doesn't work too. Still can't understand, why.

Answer 1

It seems that all you need is a simple loop:

for file in *coff*; do
  ln -s "${file}" "${file/coff-/}"
done