1
[USERNAME@host ~] echo -e 'prdxxx\ndadxxx' | grep "da*xxx"
prdxxx
dadxxx
[USERNAME@host ~] echo $SHELL
/bin/bash
[USERNAME@host ~] dpkg -l | grep -iw bash
ii  bash                                    4.1-2ubuntu3                                    The GNU Bourne Again SHell
ii  bash-completion                         1:1.1-3ubuntu2                                  programmable completion for the bash shell
[USERNAME@host ~] 

Why does da*xxx find prdxxx too? It doesn't contains da... did I found a grep bug? or is this a feature?

10

It is working fine as per the meaning of the '*'.

* -> 0 or more occurences of prev character.

Since you are checking for a*, this will match 0 or more a's. This means da*xxx can match dxxx, daxxx, daaxxx, daaaxxx, and so on.

|improve this answer|||||
  • why does "da*xxx" finds "prdxxx" string too? – gasko peter Jan 2 '13 at 8:11
  • 7
    becuase it contains dxxx. It does not matter what is before or after that. – Guru Jan 2 '13 at 8:13
4

There is a difference between normal shell file name patterns (called glob) where * matches any number of unknown characters, and regular expressions that are used for example by grep, where * stands for zero or more occurences of the previous pattern (this is the character a in your example).

|improve this answer|||||

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.