sed regex with '+' doesn't work - why?

I don't understand it. I'd like to replace the ip-up 9490:notify_rc string to ip-up ****:notify_rc. I thought it's simple:

echo "ip-up 9490:notify_rc" | sed -e 's/ip-up [0-9]+:notify_rc/ip-up ****:notify_rc/'

but no, it doesn't work for me, the output is ip-up 9490:notify_rc. Why? How can I do it?

Instead of [0-9]+ I've tried: \S+ [:num:]+ etc., tried to add -r switch to sed command, without success. The result is the original string every time.

If I change + to *, then it becomes working; but what's wrong with plus sign?

Update
Here is a short sample:

echo "ip-up 9490:notify_rc" | sed -e 's/ip-up [0-9]+:notify_rc/ip-up ****:notify_rc/'
ip-up 9490:notify_rc
echo "ip-up 9490:notify_rc" | sed -e 's/ip-up [0-9]+:notify_rc/ip-up ****:notify_rc/' -r
ip-up 9490:notify_rc
echo "ip-up 9490:notify_rc" | sed -e 's/ip-up [0-9]+:notify_rc/ip-up ****:notify_rc/' -E
ip-up 9490:notify_rc
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3 Answers

Don't put anything (except the sed script) after the -e switch.

$ echo "ip-up 9490:notify_rc" | sed -r -e 's/ip-up [0-9]+:notify_rc/ip-up ****:notify_rc/'
ip-up ****:notify_rc

You're hitting the difference between regular expression and extended regular expression.

The one or more operator is + in extended regular expression. You can tell sed that the regex is an extended one using the option -r or -E.

echo "ip-up 9490:notify_rc" | sed -r -e 's/ip-up [0-9]+:notify_rc/ip-up ****:notify_rc/'

If you use (basic) regular expression, you need to escape that operator such it is not taken as a character.

echo "ip-up 9490:notify_rc" | sed -e 's/ip-up [0-9]\+:notify_rc/ip-up ****:notify_rc/'

If there are no ohter numbers in the string to preserve you can use the following syntax:

sed -e "s/[0-9]/\*/g"

This will replace any number with an asterisk.