I am using OS X 10.10.5
and when I tried the following commands:
$ ls foo*
foo123bar.pdf
$ for f in foo*; do echo "$f" | sed -E 's:foo:bar:';done
bar123bar.pdf
$ for f in foo*; do echo "$f" | sed -E 's:foo:(&):';done
(foo)123bar.pdf
$ for f in foo*; do echo "$f" | sed -E 's:\(foo\):(\1):';done
sed: 1: "s:foo:(\1):": \1 not defined in the RE
I got an error.
My question is: how to remedy the error yielded by the last command above?