使用sed从字符串中提取子字符串

Question

I want to extract MIB-Objects from snmpwalk output. The output FILE looks like:

RFC1213-MIB::sysDescr.0.0.0.0.192.168.1.2 = STRING: "Linux debian 3.16.0-4-amd64 #1 SMP Debian 3.16.43-2+deb8u1 (2017-06-18) x86_64"
RFC1213-MIB::sysObjectID.0 = OID: RFC1155-SMI::enterprises.8072.3.2.10
..

First, I read the output file, split at character = and remove everything between RFC1213-MIB:: and .0 till the end of the string.

while read -r; do echo "${REPLY%%=*}" | sed -e 's/RFC1213-MIB::\(.*\)\.0/\1/'; done <$FILE

My current output:

sysDescr.0.0.0.192.168.1.2 
sysObjectID

How can I remove the other values? Is there a better solution of extracting sysDescr , sysObjectID ?

Answer 1

With awk:

awk -F[:.] '{print $3}'

(define : and . as field delimiters and display the 3rd field)

with sed (Gnu):

sed 's/^[^:]*::\|\.0.*//g'

(replace with the empty string all that isn't a : followed by :: at the start of the line or the first .0 and following characters until the end of the line)

Answer 2

Maybe you can try with:

sed 's/RFC1213-MIB::\([^\.]*\).*/\1/' $FILE

This will get everything that is not a dot ( . ) following the RFC1213-MIB:: string.

Answer 3

If you don't want to use sed, you can just use parameter substitution. sed is an external process so it won't be as fast as parameter substitution since it's a bash built in.

while IFS= read -r line; do line=${line#*::}; line=${line%%.*}; echo $line; done < file

line=${line#*::} assumes RFC1213-MIB does not have two colons and will be split from sysDescr with two colons.

line=${line%%.*} assumes sysDescr will have a . after it.

If you have more examples, that you think won't work, I can update my answer.