grep vs egrep vs grep -E

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# 1  
grep vs egrep vs grep -E

i am confusing in grep Vs egrep vs grep -E.could any body explains very clearly?
# 2  
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 This is the same as typing "egrep" but at some stage "egrep" may get withdrawn from the Posix standard.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:
#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"

Last edited by methyl; 01-03-2012 at 12:22 PM..
# 3  
so what you are saying is grep -E is useful while we are using extended regular expressions.right?
# 4  
It's explained better in "man grep" than I can explain.

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