I've been unable to get the "?" operator to work in SED. It works fine in GREP. Example:
echo "nathan" | sed "s/na[t]\{0,1\}han/_/g"
_
(that works)
echo "nathan" | sed "s/na[t]\?han/_/g"
nathan
(that doesn't work)
/? and /{0,1\} should be functionally identical, zero or one matches of the preceding pattern. Both work in GREP, but only the range one works in SED, and I can't find any explanation for why. I've tried different variations of escaping, quoting, and options like -E and -e.
There are 2 classes of regular expressions: BRE and ERE (basic and extended).
? by itself has no special meaning in BRE.
Nor does
+ nor
| nor
( nor
)the original grep didn't support ERE either... so egrep was developed.
nowadays grep can do both by virtue of the -E flag ... and the same should now be true for sed as well.
i.e., try
sed -E[unless you post examples of the the
sed -E expression you've already tried... we can't see what went wrong.]
