UNIX for Dummies Questions & Answers

i am confusing in grep Vs egrep vs grep -E.could any body explains very clearly?

First please mention what Operating System and version you have.

In the Posix world there is one program "grep".
The extended expression version is invoked with "grep -E". This is the same as typing "egrep" but at some stage "egrep" may get withdrawn from the Posix standard. Personally I don't believe this and persist in using "egrep".

At general user level:

Code:

#Look for one string:
grep "string"
egrep "string"
grep -E "string"

#Look for either of two strings:
egrep "string1|string2"
grep -E "string1|string2"


# Look for either of four strings:
egrep "string1|string2|string3|string4"
grep -E "string1|string2|string3|string4"

so what you are saying is grep -E is useful while we are using extended regular expressions.right?

Yes.
It's explained better in "man grep" than I can explain.