Difference of BRE(Basic Regex) and ERE(Extended Regex) on using sed, grep, awk.

 Special Chars:

BRE	.	[	\			*					^	$
ERE	.	[	\	(	)	*	+	?	{	|	^	$

ex. pattern for abc-adafaadsf abc adaadefaa 

BRE: abc\|def
ERE: abc|def

ex. pattern for match count.

BRE: abc\{3,5\}
ERE: abc{3,5}

so, when using command of awk, grep, sed. don't forget using -r for ERE(extended regex). 

but, when writing a shell script, using BRE is better, because 6 chars of 「.[\*^$」 are specials,

but there more special chars 「.[\()*+?{|^$」 for ERE. 

Which is better, as you select.