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Good catch. This seems indeed to be a bug in grep (Tested with GNU grep 3.4 and 3.7):

grep -ow "n[0-9]=*"
grep -Eow "n[0-9]=*"

return only first match (or probably rather matches only the first one),
while ...

grep -Pow "n[0-9]=*"

... returns all matches as expected.

To report bugs for GNU grep, check here.

Good catch. This seems indeed to be a bug in grep (Tested with GNU grep 3.4 and 3.7):

grep -ow "n[0-9]=*"
grep -Eow "n[0-9]=*"

return only first match (or probably rather matches only the first one),
while ...

grep -Pow "n[0-9]=*"

... returns all matches as expected.

To report bugs for GNU grep, check here.

However, I cannot confirm your observation that -P [...] doesn't seem to keep the -w description, for me (GNU grep 3.4 and 3.7), the command outputs as expected:

$ echo 'n1=1 n2= n3=3 n4=' | grep -owP "n[0-9]=*"
n1
n2=
n3
n4=

Good catch. This seems indeed to be a bug in grep (Tested with GNU grep 3.4):

grep -ow "n[0-9]=*"
grep -Eow "n[0-9]=*"

return only first match (or probably rather matches only the first one),
while ...

grep -Pow "n[0-9]=*"

... returns all matches as expected.

To report bugs for GNU grep, check here.

You can work around that by not using -w, but specify word boundaries:

grep -o '\<n[0-9]=*\>'

Good catch. This seems indeed to be a bug in grep (Tested with GNU grep 3.4 and 3.7):

grep -ow "n[0-9]=*"
grep -Eow "n[0-9]=*"

return only first match (or probably rather matches only the first one),
while ...

grep -Pow "n[0-9]=*"

... returns all matches as expected.

To report bugs for GNU grep, check here.

Good catch. This seems indeed to be a bug in grep (Tested with GNU grep 3.4):

grep -ow "n[0-9]=*"
grep -Eow "n[0-9]=*"

return only first match (or probably rather matches only the first one),
while ...

grep -Pow "n[0-9]=*"

... returns all matches as expected.

To report bugs for GNU grep, check here.

But note, that the pattern doesn't make all too much sense.

= is not a valid word character, so the quantifier * will always and necessarily evaluate to 0 times. So, you can simply leave it out, which will then make grep to work as expected. This ...

grep -ow "n[0-9]"

... returns all matches.

Btw, sed works as expected, e.g. this ...

sed 's/n[0-9]=*//g'

... removes all occurencies.

Good catch. This seems indeed to be a bug in grep (Tested with GNU grep 3.4):

grep -ow "n[0-9]=*"
grep -Eow "n[0-9]=*"

return only first match (or probably rather matches only the first one),
while ...

grep -Pow "n[0-9]=*"

... returns all matches as expected.

To report bugs for GNU grep, check here.

You can work around that by not using -w, but specify word boundaries:

grep -o '\<n[0-9]=*\>'