is there any named regular expression capture for grep? - regex

Question

i'd like to know if its possible to get named regular expression with grep -P(linux bash) from a non formatted string? well.. from any string
For example:
John Smith www.website.com john#website.com jan-01-2001
to capture as
$name
$website
$email
$date
but it seems I cant pass any variables from output?
echo "www.website.com" | grep -Po '^(www\.)?(?<domain>.+)$' | echo $domain
has no output

Answer 1

no. grep is a process. you are talking about environment propagation from child to parent. that's forbidden.
instead, you can do
DATA=($your_line)
then take name=DATA[0] so and forth.
or another way using awk:
eval "`echo $your_line | awk '
function escape(s)
{
gsub(/'\''/,"'\''\"'\''\"'\''", s);
s = "'\''"s"'\''";
return s;
}
{
print "name="escape($1);
print "family_name="escape($2);
print "website="escape($3);
print "email="escape($4);
print "date="escape($5);
}'`"
the sense here is to propagate the info via stdout and eval it in the parent environment.
notice that, here, escape function will escape any string correctly such that nothing will be interpreted wrongly(like the evil of quotes).
following is the output from my jessie:
name='John'
family_name='Smith'
website='www.website.com'
email='john#website.com'
date='jan-01-2001'
if the family name is O'Reilly, the eval result will still be correct:
name='John'
family_name='O'"'"'Reilly'
website='www.website.com'
email='john#website.com'
date='jan-01-2001'

Answer 2

Grep is an independent command-line utility; it does not run inside of bash. So it couldn't create bash variables even if it wanted to.
However, bash has a regular expression matcher built-in. It's not a perl-compatible regex matcher, so it doesn't implement named captures. (To be precise, it matches Posix extended regular expressions, the same as grep -E.) But it does implement numbered captures.
You do regular expression matches with the =~ operator inside of the [[ ... ]] compound command syntax. If the regular expression matches, then the expression succeeds, and the captures are inserted into the array variable BASH_REMATCH. ${BASH_REMATCH[0]} will be the entire matched substring, and the remaining elements, starting with ${BASH_REMATCH[1]}, will be the individual captures in order.
For example:
$ url=www.example.com
$ [[ $url =~ ^(www\.)?(.*) ]]
$ echo "${BASH_REMATCH[1]}"
www.
$ echo "${BASH_REMATCH[2]}"
example.com