grep not matching exact string

user_12775995 0
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I'm a bit troubled by grep not behaving as expected. I'm trying to extract hosts from a sort of dictionary, structured like OLD_HOST_NAME;NEW_HOST_NAME, and some of them have the same prefix, like "HOST-1-2". I want to only match "HOST-1-2", but independently from which option I pass to grep, it keeps returning all the strings with the same prefix instead of matching only the exact string, i.e.:

grep -F "HOST-1-2" dict.txt
HOST-1-2-3;NEW_HOST-1-2-3
HOST-1-2-4;NEW_HOST-1-2-4
HOST-1-2-5;NEW_HOST-1-2-5

I tried several options, like grep -w "HOST-1-2", grep -e '\HOST-1-2\b', grep -e '\HOST-1-2\b', grep -Po "\bHOST-1-2\b" (that actually match what I want, but it does it for all occurrences of the substring so it's still not working), tried mixing them, but at the end of the day I'm still not getting what I need.

Any idea on how to achieve what I want, in order for grepping only "HOST-1-2" without all the other partial matches?

EDIT: Sorry to not have specified more clearly, the dictionary sample is the one I already shown as result of the wrong substring matching crep:

old_host;new_host
SERVER-1;NEW_SERVER-1
HOST-1-2-3;NEW_HOST-1-2-3
HOST-1-2-4;NEW_HOST-1-2-4
HOST-1-2-5;NEW_HOST-1-2-5

I already stated what I want to achieve though:

in order for grepping only "HOST-1-2" without all the other partial matches

grep
2 Answers

You may use this grep:

grep -E '(^|;)HOST-1-2(;|$)' file

Which means:

  • -E: Enable extended regex mode
  • (^|;): Match start or ;
  • HOST-1-2: Match HOST-1-2
  • (;|$): Match ; or end
user_5482250

You can use grep -o to print only the matching part of the lines and add a word boundary after the 2 and before the H

grep -o '\<HOST-1-2\>' ./dict.txt

Output

HOST-1-2
HOST-1-2
HOST-1-2

If you only want to print the first matches:

grep -oP '^.*?\b\KHOST-1-2\b' ./dict.txt
user_54249880
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