Difference between XPath and css selector

https://gist.github.com/slotix/11f0930b2d46d2946249a10e6216735b#file-css3vsxpath-csv

	Goal	CSS 3	XPath
	All Elements	*	//*
	All P Elements	p	//p
	All Child Elements	p>*	//p/*
	Element By ID	#foo	//*[@id=’foo’]
	Element By Class	.foo	//*[contains(@class,’foo’)]
	Element With Attribute	*[title]	//*[@title]
	First Child of All P	p>*:first-child	//p/*[0]
	All P with an A child	Not possible	//p[a]
	Next Element	p + *	//p/following-sibling::*[0]
	Previous Element	Not possible	//p/preceding-sibling::*[0]

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.

.net Regex Replace MatchEvaluator

 public delegate string MatchEvaluator(Match match);

Examples

using System; using System.Text.RegularExpressions; class MyClass { static void Main(string[] args) { string sInput, pattern; // The string to search. sInput = "aabbccddeeffcccgghhcccciijjcccckkcc"; // A very simple regular expression. pattern = "cc"; Regex r = new Regex(pattern); // Assign the replace method to the MatchEvaluator delegate. MatchEvaluator myEvaluator = new MatchEvaluator(ReplaceCC); // Write out the original string. Console.WriteLine(sInput); // Replace matched characters using the delegate method. sInput = r.Replace(sInput, myEvaluator); // Write out the modified string. Console.WriteLine(sInput); } // Replace each Regex cc match with the number of the occurrence.

public static string ReplaceCC(Match m)

{ i++; return i.ToString() + i.ToString(); } public static int i=0; } // The example displays the following output: // aabbccddeeffcccgghhcccciijjcccckkcc // aabb11ddeeff22cgghh3344iijj5566kk77

linux sed replace with single/double quotation

$ echo \"aaaa\" | sed 's/"/1/g'
>1aaaa1

$ echo \'aaaa\' | sed 's/'\''/1/g'
>1aaaa1